PROGRAM & ABSTRACTS GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices - TU Berlin

 
 
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
P R O G RA M & ABSTRAC TS
GraFOx Summer School
on Oxide Semiconductors for Smart Electronic Devices

3 – 9 June 2019

Centro Italo-Tedesco per l'Eccellenza Europea (Villa Vigoni),
Loveno di Menaggio (CO), Lago di Como, Italia
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
Program & Abstracts




Table of Content

Welcome���������������������������������������������������������������������������������������������������������������������������������������� 3
Program ��������������������������������������������������������������������������������������������������������������������������������������� 4
Speakers ��������������������������������������������������������������������������������������������������������������������������������������� 6
Social Activities ��������������������������������������������������������������������������������������������������������������������������� 6
Program Committee ������������������������������������������������������������������������������������������������������������������ 8
Summer School Organization ������������������������������������������������������������������������������������������������ 11
Abstracts ������������������������������������������������������������������������������������������������������������������������������������ 13
Map Villa Vigoni ����������������������������������������������������������������������������������������������������������������������� 79




2                                                                                                                                                    GraFOx Summer School
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
Welcome




GraFOx Summer School
on Oxide Semiconductors for Smart Electronic Devices


Dear colleagues,

I would like to extend a warm welcome to all participants of the GraFOx Summer School.
Our particular gratitude goes to our group of renowned lecturers who have made the
effort to join us here at Lake Como in Italy.

Our Berlin scientific network GraFOx has now been running for almost three years and
has led to many intensive collaborations within and with external partners. It is a great
example that a collaborative action can be much more than the sum of individual activ-
ities.

Most of our work is carried by our Ph.D. students and we are very grateful for their com-
mitment and enthusiasm. With this Summer School we want to provide a forum for in-
depth learning from international experts and for presenting their work.

At this point, I would also like to thank Kai Hablizel and Holger Eisele for organizing our
meeting in such a wonderful environment.

Wishing you a fruitful and inspiring event,



Henning Riechert
Paul-Drude-Institut für Festkörperelektronik, Berlin
Speaker of GraFOx
grafox.pdi-berlin.de




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                           3
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
Program




Program



 Time / Day    Monday 3.6.                Tuesday 4.6.                  Wednesday 5.6.                   Thursday 6.6.
 08:00-09:00                                                                      Breakfast

 09:00-09:05                              A0: Henning Riechert
                                                                        L3: Claudine Noguera             L4: Joachim Würfl
 09:10-11:00                              L1: Shizuo Fujita

 11:00-11:30                              Coffee                                               Coffee and Posters

 11:30-11:45                                                                                             T41: Feljin Jose

 11:45-11:50                                                                                             P42: Nicoleta G. Apostol
                                          T11: Oliver Bierwagen         T31: Susi Lindner
 11:50-11:55                                                                                             P43: Ioana Lalau

 11:55-12:00                                                                                             P44: Anatoly Kozlov

 12:00-12:05                                                                                             P45: Hannah Morgan-Cooper
                                                                        T32: Celina Schulze
 12:05-12:15            Arrival           T12: Piero Mazzolini

 12:15-12:30                                                            T33: Felix Reichmann

 12:30-12:35                              P13: Melanie Budde            P34: Johannes Feldl

 12:35:12:40                              P14: Andreea Costas           P35: Elena Maznitsyna
                                                                                                         P49: Poster Viewing
 12:40-12:45                              P15: Georg Hoffmann           P36: Marie Bischoff

 12:45-12:50                              P16: Alexandra Papadogianni   P37: Chiara Groppi

 12:50-12:55                              P17: Kyoung-Ho Kim            P38: Melania Loredana Onea

 12:55-13:00                              P18: Aykut Baki               P39: Ovidiu Cojocaru

 13:00-14:30                                                                         Lunch

 14:30-15:30
                                          L2: Lena F. Kourkoutis                                         L5: Roberto Fornari
 15:30-16:30

 16:30-17:00                              Coffee & poster session                                        Coffee & poster session

 17:00-17:05                                                                                             P51: Jacopo Remondina

 17:05-17:10      Shuttle bus transfer                                                                   P52: Nazir Jaber

 17:10-17:15           from MXP                                                                          P53: Carmine Borelli
                                          T21: Tobias Schulz
 17:15-17:20                                                                                             P54: Philipp John

 17:20-17:25                                                                                             P55: Emroj Hossain

 17:25-17:30                                                                                             P56: Maneesha Narayanan

 17:30-17:35                              P22: Marian Cosmin Istrate    EII: Boat Trip

 17:35-17:40                              P23: Vincenzo Montedoro

 17:40-17:45                              P24: Lukas Zeinar

 17:45-17:50                              P25: Patrick Salg

 17:50-17:55                              P26: Cristian Radu
                Check-in & Registration                                                                  L6: Michael Heuken
 17:55-18:00                              P27: Alexander Karg

 18:00-18:15
                                          EI: German Culture and
 18:15-18:30
                                          History
 18:30-19:00

 19:00-19:30

 19:30-21:30     Aperitivo di Benvenuto   Dinner                        Dinner on your own               Dinner




4                                                                                                          GraFOx Summer School
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
Program




Friday 7.6.                          Saturday 8.6.                     Sunday 9.6.                     Time / Day
                                                      Breakfast                                        08:00-09:00

                                                                                                       09:00-09:05
L7: Chris van de Walle               L8: Debdeep Jena                      Checkout and Bus Transfer
                                                                                                       09:10-11:00
                                                                                    to MXP
                           Coffee and Posters                                                          11:00-11:30

                                     T81: Christian Golz                                               11:30-11:45
T71: Konstantin Lion
                                     P82: Martina Zupancic                                             11:45-11:50

P72: Sebastian Tillack               P83: Robin Ahrling                                                11:50-11:55

P73: Joe Willis                      P84: Johannes Boy                                                 11:55-12:00

                                     P85: Taylor Moule                                                 12:00-12:05

                                                                                                       12:05-12:15

                                                                                                       12:15-12:30

                                                                                                       12:30-12:35

P79: Poster Viewing                                                                                    12:35:12:40
                                     P89: Poster Viewing
                                                                                                       12:40-12:45

                                                                                                       12:45-12:50

                                                                                                       12:50-12:55

                                                                                                       12:55-13:00

                                 Lunch                                                                 13:00-14:30

                                                                                                       14:30-15:30
                                     L9: Regina Dittmann
                                                                                                       15:30-16:30

                                     Coffee & poster session                                           16:30-17:00
                                                                                  Departure
                                                                                                       17:00-17:05

                                                                                                       17:05-17:10

                                                                                                       17:10-17:15
                                     T91: Roxana-Elena Patru
                                                                                                       17:15-17:20

                                                                                                       17:20-17:25

                                                                                                       17:25-17:30

EIII: City Tour                                                                                        17:30-17:35

                                                                                                       17:35-17:40

                                                                                                       17:40-17:45
                                     T92: Neculai Plugaru
                                                                                                       17:45-17:50

                                                                                                       17:50-17:55

                                                                                                       17:55-18:00

                                     T93: Julian Stöver                                                18:00-18:15

                                     O99: Holger Eisele                                                18:15-18:30

                                                                                                       18:30-19:00
                                     Poster removal
                                                                                                       19:00-19:30

Dinner on your own                   Dinner                                                            19:30-21:30




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                                  5
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
Speakers




Speakers

The following highly recognized researchers in the field of oxide ­semiconductors
will give introductional tutorial talks and form the nucleus for related PhD
student talks and posters presentations.


• L1: Shizuo Fujita (Kyoto University, Japan):
  Growth and Characterization of Layered Oxide Materials
• L2: Lena F. Kourkoutis (Cornell University, Ithaca/NY, U.S.A.):
  TEM and Characterization of Point Defects
• L3: Claudine Chopin-Noguera (CNRS INSP and Sorbonne Université,
  Orsay/Paris, France):
  Oxide Surfaces − Theory and Experiments
• L4: Joachim Würfl (Leibniz Ferdinand-Braun-Institut für
  Höchstfrequenztechnik, Berlin, Germany):
  Oxide Semiconductor Devices and Applications
• L5: Roberto Fornari (Università degli Studi di Parma, Italia):
  Bulk Oxide Growth and Crystallography
• L6: Michael Heuken (Aixtron SE and RWTH Aachen, Herzogenrath,
  Germany):
  Introduction into World-Leading Semiconductor Industry
• L7: Chris G. van de Walle (University of California at Santa
  Barbara, CA, U.S.A.):
  Calculations of Oxide Materials Properties
• L8: Debdeep Jena (Cornell University, Ithaca/NY, U.S.A.):
  Transport in Oxide Materials
• L9: Regina Dittmann (Forschungszentrum Jülich, Germany):
  Effects in Oxide Materials: Ferroelectricity, Memrestivity, and
  Piezoelectricity




6                                                                                  GraFOx Summer School
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
Social Activities




Social Activities

Joint meals and social activities such as a boat trip on Lake Como within the
triangle of Menaggio, Bellagio and Varenna and a guided tour through the city
of Como on the footsteps of Alessandro Volta (inventor of the electric bat-
tery) complete the scientific program of the Summer School and encourages
opportunities for exchange, even outside of science.

Villa Mylius-Vigoni and the park are open exclusively to our participants for a
guided tour on the German-Italian culture and history of the villa.



Boat trip on Wednesday, 05 June 2019

14:30: 		Walk to Menaggio
15:00: 		Departure of the boat
15:00-16:00: Tour to Tremezzina and surroundings,
             different villas and the island of Comaci
16:00-19:30: Tour to Bellagio and Varenna
19:30: 		Return to Menaggio
From 20:00:  Individual dinner in Menaggio
             (or together in a restaurant: tbd)

City Tour Como on Friday, 07 June 2019

14:45: 		Meeting at Villa Vigoni
15:00: 		Departure shuttle bus to Como
16:00-18:00: Como City on the footsteps of Alessandro Volta
21:30:       Individual time/dinner
21:30:       Departure shuttle bus to Villa Vigoni




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                         7
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
Program Committeee




Program Committeee

                     Martin Albrecht
                     Ph.D. in Physics
                     Head of Department “Materials Science“
                     Leibniz-Institut für Kristallzüchtung, Berlin, Germany




                     Martin Albrecht was born in Hamburg and studied Physics at the University
                     of Hamburg Germany. He completed his Ph.D. thesis at Erlangen University
                     in 1995. Since 2004 he leads the electron microscopy group at Leibniz-Institut
                     für Kristallzüchtung and since 2017 its department for “Materials Science”.
                     He works in the field of elementary growth and relaxation mechanisms of
                     semiconductor heterostructures as well as on structure- property relations of
                     semiconductors and nanostructures by means of electron microscopy tech-
                     niques. As a co-founder of and PI in GraFOx he sees oxide semiconductors as
                     an exciting field of research, where discoveries can be made with the perspec-
                     tive to develop novel devices.




                     Oliver Bierwagen
                     Ph.D. in Experimental Solid-State Physics
                     Paul-Drude-Institut für Festkörperelektronik,
                     Leibniz Institut im Forschungsverbund Berlin e. V., Berlin, Germany


                     Oliver Bierwagen received his Ph.D. in experimental solid-state physics from
                     Humboldt-Universität zu Berlin, Germany, in 2007. From 2008–2010 he has
                     been working as post-doc at the University of California, Santa Barbara, USA.
                     Since 2011 he has been working as senior scientist and PI at Paul-Drude-In-
                     stitut für Festkörperelektronik, Berlin, Germany. His research interests in-
                     clude the fundamentals of MBE growth and transport properties, as well as
                     the gas-sensing application of semiconducting oxides. Oliver Bierwagen is
                     co-founder and PI of four GraFOx projects and shares responsibility for the
                     scientific coordination of GraFOx with Martin Albrecht from the Leibniz-Insti-
                     tut für Kristallzüchtung.




8                                                                            GraFOx Summer School
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
Program Committeee




Melanie Budde
MSc., Ph.D. candidate
Paul-Drude-Institut für Festkörperelektronik,
Leibniz Institut im Forschungsverbund Berlin e. V., Berlin, Germany


Melanie Budde was born in Hannover, Germany and studied Nanotechnolo-
gy with a focus on semiconductor technology, physics of nanostructures and
surfaces there between 2010 and 2016. Her Ph.D. thesis is on the MBE growth
and doping of p-type oxides. She sees GraFOx as an opportunity to continue
her research in oxides using MBE growth combined with the chance to work in
an interdisciplinary environment.




Holger Eisele
Professor in Experimental Physics
Technische Universität Berlin, Germany




Holger Eisele was born in Mannheim, Germany, and studied Physics at the
Technische Universität Berlin, Germany. He completed his Ph.D. thesis 2001.
He works on the structural and electronic characterization of semiconductor
material, surfaces and nanostructures, using surface investigation methods,
such as scanning tunneling microscopy and spectroscopy. As a PI in GraFOx,
he sees oxide semiconductors as a research field to develop novel materials
based application for sustainable technology.




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                      9
PROGRAM & ABSTRACTS - GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices
Program Committeee




                     Henning Riechert
                     Professor in Experimental Physics / Material Science
                     Paul-Drude-Institut für Festkörperelektronik,
                     Leibniz Institut im Forschungsverbund Berlin e. V.


                     Henning Riechert was born in Hannover, Germany. He studied Physics at the
                     Rheinische Friedrich-Wilhelms-Universität Bonn and completed his PhD (1986)
                     in Physics at the Universität Köln, Germany. Subsequently he started his pro-
                     fessional career as staff scientist at Siemens AG in Munich and continued as
                     project manager at Infineon Technologies, Munich, where he realized the first
                     InGaN/GaN LED in Europe. He headed the department of photonics at In-
                     fineon Corporate Research where he succeeded to realize the first monolithic
                     1.3µm VCSEL worldwide and transferred it to production. As senior principal
                     scientist, he was responsible for materials science at Qimonda AG, Dresden,
                     Germany, until 2007. Henning Riechert is Director of the Paul-Drude-Institut
                     für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e. V.
                     and Professor at the Institute for Physics at Humboldt-Universität zu Berlin,
                     Germany. Since 2016, he has been Speaker of Leibniz ScienceCampus GraFOx
                     (“Growth and Fundamentals of Oxides for Electronic Applications”) in Berlin.




                     Julian Stoever
                     MSc., Ph.D. candidate
                     Leibniz-Institut für Kristallzüchtung, Berlin, Germany




                     Julian Stoever was born in a small town in northern Germany and studied
                     Physics at the University of Bremen, Germany. After his guest stay at the Fer-
                     dinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik in Berlin in
                     2015, he spent one and a half years as a researcher at the Wroclaw Research
                     Center EIT+ in Poland. Starting in 2017, he is a Ph.D. student at Leibniz-In-
                     stitut für Kristallzüchtung within the GraFOx network and deals with the
                     defect characterization of oxide semiconductors for resistive switching. His
                     main methods are electrical characterization techniques such as IV/CV, Hall
                     effect measurements and deep-level transient spectroscopy as well as optical
                     spectroscopy.




10                                                                           GraFOx Summer School
Summer School Organization




Summer School Organization

Kai Hablizel
Dipl.-Biologist and certified EU Research Officer
Paul-Drude-Institut für Festkörperelektronik,
Leibniz Institut im Forschungsverbund Berlin e. V., Berlin, Germany


Kai Hablizel holds a Diploma in Biology. She studied Cell Biology and Genet-
ics at the University of Karlsruhe (TH) in Karlsruhe and the German Cancer
Research Center (DKFZ) in Heidelberg, Germany. After completing her stud-
ies, she spent over 10 years developing and implementing scientific commu-
nication programs for the healthcare industry. During this time, she lived and
worked in Germany and Italy (Milan). In 2012, she returned to an academic
setting and back to Germany. As European Research Administrator for Policy
and Funding, she advices and provides individual support to scientific grant
applicants and projects implementers in European research programs and
policies. Since 2017, she also coordinates the Leibniz ScienceCampus GraFOx
at the Paul-Drude Institute für Festkörperelektronik, Leibniz-Institut im For-
schungsverbund Berlin e. V.




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                11
Program & Abstracts




12                   GraFOx Summer School
Abstracts



Abstracts

Tuesday, 4 June 2019                                                                    Session 5: Chair: Melanie Budde/Julian Stöver


Session 1: Chair: Henning Riechert                                                      L5: Roberto Fornari��������������������������������������������������������        51
                                                                                        P51: Jacopo Remondina�����������������������������������������������               53
L1: Shizuo Fujita ������������������������������������������������������������    14   P52: Nazir Jaber ������������������������������������������������������������      55
T11: Oliver Bierwagen���������������������������������������������������          17   P53: Carmine Borelli �����������������������������������������������������         56
T12: Piero Mazzolini ������������������������������������������������������       18   P54: Philipp John �����������������������������������������������������������      57
P13: Melanie Budde��������������������������������������������������������        19   P55: Emroj Hossain��������������������������������������������������������         58
P14: Andreea Costats���������������������������������������������������           20   P56: Maneesha Narayanan �����������������������������������������                  59
P15: Georg Hoffmann ��������������������������������������������������            21
P16: Alexandra Papadogianni��������������������������������������                 22   Session 6: Chair Holger Eisele
P17: Kyoung-Ho Kim �����������������������������������������������������          23
P18: Aykut Baki ��������������������������������������������������������������    24   L6: Michael Heuken�������������������������������������������������������� 60


Session 2: Chair: Martin Albrecht
                                                                                        Friday, 7 June 2019
L2: Lena F. Kourkoutis ��������������������������������������������������         25
T21: Tobias Schulz ���������������������������������������������������������      27   Session 7: Chair: Susi Lindner
P22: Marian Cosmin Istrate�����������������������������������������               28
                                                                                        L 7: Chris van de Walle��������������������������������������������������          63
P23: Vincenzo Montedoro ��������������������������������������������              29
                                                                                        T71: Konstantin Lion�����������������������������������������������������          64
P24: Lukas Zeinar�����������������������������������������������������������      30
                                                                                        P72: Sebastian Tillack���������������������������������������������������          65
P25: Patrick Salg �����������������������������������������������������������     31
                                                                                        P73: Joe Willis�����������������������������������������������������������������   66
P26: Cristian Radu���������������������������������������������������������       32
P27: Alexander Karg������������������������������������������������������         33
                                                                                        Saturday, 8 June 2019
Wednesday, 5 June 2019
                                                                                        Session 8: Chair: Nicoleta G Apostol

Session 3: Chair: Piero Mazzolini
                                                                                        L8 Debdeep Jena�����������������������������������������������������������         67
                                                                                        T81: Christian Golz��������������������������������������������������������        69
L3: Claudine Noguera ���������������������������������������������������          34
                                                                                        P82: Martina Zupancic��������������������������������������������������            70
T31: Susi Lindner �����������������������������������������������������������     36
                                                                                        P83: Robin Ahrling ���������������������������������������������������������       71
T32: Celina Seraphin Schulze ��������������������������������������               37
                                                                                        P84: Johannes Boy ��������������������������������������������������������         72
T33: Felix Reichmann�����������������������������������������������������         38
                                                                                        P85: Taylor Moule�����������������������������������������������������������       73
P34: Johannes Feldl ������������������������������������������������������        39
P35: Elena Maznitsyna��������������������������������������������������           40
P36: Marie Bischoff��������������������������������������������������������       41   Session 9: Chair: Oliver Bierwagen
P37: Chiara Groppi��������������������������������������������������������        42
                                                                                        L9: Regina Dittmann�����������������������������������������������������           74
P38: Melania Loredana Onea��������������������������������������                  43
                                                                                        T91: Roxana-Elena Patru ���������������������������������������������              75
P39: Ovidiu Cojocaru�����������������������������������������������������         44
                                                                                        T92: Neculai Plugaru �����������������������������������������������������         76
                                                                                        T93: Julian Stöver�����������������������������������������������������������      77
Thursday, 6 June 2019

Session 4: Chair: Tobias Schulz

L4: Joachim Würfl ���������������������������������������������������������       45
T41: Feljin Jose���������������������������������������������������������������   46
P42: Nicoleta G. Apostol�����������������������������������������������           47
P43: Ioana Lalau ������������������������������������������������������������     48
P44: Anatoly Kozlov��������������������������������������������������������       49
P45: Hannah Morgan-Cooper��������������������������������������                   50



Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                                                                                    13
L1: Shizuo Fujita                                                                                        Tu 09:15-11:00




                                  Epitaxial Growth Technologies of
                                  Oxide Semiconductor Thin Films
                                                    Shizuo Fujita
                                               Kyoto University, Japan
                                           Email: fujitasz@kuee.kyoto-u.ac.jp


                         Modern growth technologies such as molecular beam epitaxy (MBE)
                     and metalorganic chemical vapor deposition (MOCVD) are applicable to
                     the growth of oxide semiconductor thin films. However, different from non-
                     oxide semiconductors, highly-reactive oxygen sources may cause severe pre-
                     reactions with other sources and give damages to components of the reaction
                     system. In order to avoid formation of oxygen vacancies, which are known to
                     affect properties of oxide semiconductors, we need to grow oxide semiconduc-
                     tors under sufficient overpressure of oxygen, like other semiconductors such
                     as GaAs and GaN. In MOCVD of ZnO, for example, dimethylzinc (DMZn)
                     or diethylzinc (DEZn), which is generally used as a zinc source, is highly
                     reactive with oxygen (O2 ) gas. We, therefore, may have to use nitrous oxide
                     (N2 O) or nitrogen dioxide (NO2 ) instead of oxygen gas. This, however, in-
                     creases possibility of forming oxygen vacancies; this is a dilemma One of the
                     solutions is to design the system configuration to avoid prereaction between
                     the source precursors while using an active oxygen source.
                         We have developed the mist CVD technology, where in the growth of
                     ZnO water or alcohol solution of zinc compounds such as zinc acetate and
                     zinc acetylacetone, are ultrasonically atomized and the mist particles formed
                     by the atomization are transferred by a carrier gas to the reaction area like a
                     gas source. We may choose non-toxic and safe chemicals as source precursors
                     as well as chlorides and bromides which are free from carbon. The solvent,
                     water or alcohol, can be an oxygen source or we may use O2 gas as a carrier
                     gas to enhance the oxygen partial pressure in the growth atmosphere. The
                     mist CVD offers opportunity to grow a variety of oxides including ZnO and
                     Ga2 O3 at low cost with a simple growth system.
                         Using sapphire as an inexpensive and high quality substrate, we have
                     achieved the growth of single-crystalline corundum-structured α-Ga2 O3 , fol-
                     lowed by n-type doing, band gap tuning by α-(Al,Ga)2 O3 and α-(In,Ga)2 O3
                     alloys, and formation of heterostructures [1]. FLOSFIA Inc. developed α-
                     Ga2 O3 Schottky barrier diodes (SBDs) with record-low on-resistance [2] and
                     the TO220-packaged SBDs showed fast switching characteristics and rea-
                     sonable heat resistance comparable to an actual SiC SBD device [3]. Since
                     α-Ga2 O3 devices are fabricated by mist CVD on sapphire substrates and the
                     device size can be small owing to the low on-resistance, the device cost can
                     be markedly low. The α-Ga2 O3 power devices, therefore, may be accepted
                     even for home appliances in which SiC and GaN devices are hardly used due




14                                                                                             GraFOx Summer School
L1: Shizuo Fujita                                                                                    Tu 09:15-11:00




                     to their high cost.
                         As one of other topical materials, the author emphasizes ultra-wide
                     bandgap rocksalt-structured Mg-rich Mgx Zn1−x O alloys (x of between ∼0.5
                     and 1). They offer opportunity to deep ultraviolet (DUV) luminescence be-
                     tween ∼4.5 eV and 7.8 eV. Our efforts have been focused on the growth of
                     MgZnO films on MgO substrates by mist CVD using chlorides of Mg and
                     Zn in order to eliminate carbon contamination. Atomically-flat surface of
                     MgZnO films, composed of step-terrace structure with the step height of
                     diatomic length, was evidenced by atomic force microscopy (AFM). This
                     suggests the successful layer-by-layer growth. The transmission microscope
                     (TEM) image scarcely showed interface roughness between the MgZnO layer
                     and the MgO substrate as well as dislocation lines in the MgZnO film. The
                     dislocation density in the Mg0.92 Zn0.08 O film is estimated to be less than
                     107 cm−2 .
                         Optical properties of MgZnO films were characterized by optical trans-
                     mission spectroscopy and cathodoluminescence (CL) study with the accel-
                     eration beam energy of 5 kV at 6–300 K. For the Mg0.95 Zn0.05 O film, the
                     CL peak was at 6.24 eV (199 nm) at 6 K, that is, it was in the vacuum
                     ultraviolet (VUV) region. This is the shortest emission wavelength among
                     the previous reports of the luminescence of MgZnO epitaxial films. We ob-
                     served the clear DUV luminescence also at 300 K peaking at 6.05 eV (205
                     nm). Spectrally integrated CL intensity at 300 K over that at 6 K (I300 /I6 ),
                     which is supposed to be the internal quantum efficiency at 300 K, was about
                     2.6 %. Optical transmission spectroscopy revealed that the optical band gap
                     of this sample was about 6.6 eV. Then, there is a large Stokes-like shift of
                     about 0.5 eV between the band gap and the DUV CL peak energy. One of
                     the reasons for this large Stokes-like shift is proposed to be the band gap
                     fluctuation induced by different local arrangement of Mg and Zn atoms in
                     the alloy [4].
                         In the lecture, the author summarizes the overall view of epitaxial growth
                     technologies of oxide semiconductors with the empashis on the up-to-date
                     results achieved by novel growth technologies.
                     References
                     [1] S. Fujita et al., Jpn. J. Appl. Phys. 55, 1202A3 (2016).
                     [2] M. Oda et al., Appl. Phys. Express 9, 021101 (2016).
                     [3] K. Kaneko et al., Jpn. J. Appl. Phys. 57, 02CB18 (2018).
                     [4] T. Onuma et al., Appl. Phys. Lett. 113, 061903 (2018).




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                         15
L1: Shizuo Fujita                                                                                                                                Tu 09:15-11:00




                                                           quartz tube

                                                                                                                               exhaust
                                                                                substrate
                                            flow meter
                                                                mist
                                            flow meter
                                                                    source
                                                                    solution                                               heater
                                                water
                             carrier gas                           ultrasonic     Fig. 1. An example of system
                             (N2 or O2)                            transducer     configurations of mist CVD equipment.

                                          a-axis Lattice Constant [Å]
                                         4.7       5              5.5
                                     9
                                               α-Al2O3

                                     8
                     Band Gap [eV]




                                     7              α-(Al,Ga)2O3


                                     6
                                                                                                 Fig. 4. An AFM surface image of
                                     5    α-Ga2O3                                                the Mg.92Zn0.08O film.
                                                         α-(In,Ga)2O3
                                                               α-In2O3
                                     4
                                                                                                             Wavelength [nm]
                                    1.9      2      2.1     2.2                                    600 400                       200
                                     Averaged Bond Length [Å]                                        (a)#1 (x=0.95)         6K
                             Fig. 2. Bandgaps of α-(Al,Ga)2O3 and                                                       300K
                             α-(In,Ga)2O3 alloys.                                                                       (x25)

                                                                                                          (b)#2 (x=0.92) 6K
                                                                                    CL Intensity [a.u.]




                                                                                                                     300K
                                                                                                                     (x50)

                                                                                                          (c)#3 (x=0.81)         6K
                                                                                                            300K
                                                                                                            (x50)

                                                                                                          (d)#4 (x=0.74)       6K
                                                                                                                  300K
                                                                                                                  (x50)

                                                                                                      2      3      4      5        6    7
                                                                                                           Photon Energy [eV]
                                                                                                           Fig. 5. CL spectra of MgxZn1-xO
                             Fig. 3. Cross sectional TEM and SEM images of                                 film of different x at the
                             a Ga2O3 layer on sapphire with SiO2 masks                                     temperatures of 6 and 300 K.
                             fabricated by epitaxial layer overgrowth (ELO).




16                                                                                                                                     GraFOx Summer School
T11: Oliver Bierwagen                                                                                  Tu 11:30-12:00




                          Molecular Beam Epitaxy, Transport Measurements, Gas
                                                Sensing
                                                     Oliver Bierwagen
                              Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im
                                              Forschungsverbund Berlin e.V.
                                                Email: bierwagen@pdi-berlin.de


                            Working as senior scientist and GraFOx-PI at PDI I am dealing with the
                         fundamentals of molecular beam epitaxy of oxides, with transport measure-
                         ments, and have a particular interest in the fundamentals of oxide-based gas
                         sensing.
                            Depending on the schedule I would give a talk on oxide-based gas sensing
                         “Fundamentals of gas sensing revealed by single-crystalline oxide films” or
                         methods of transport measurements “Bulk and surface charge transport in
                         semiconducting oxides”.




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                           17
T12: Piero Mazzolini                                                                                           Tu 12:00-12:30




                            Growth and Characterization of Epitaxial Ga2 O3
                               Thin Films via Molecular Beam Epitaxy
                            P. Mazzolini1 , P.Vogt1 , R. Schewski2 , C. Wouters2 , A. Falkenstein3 ,
                                 M. Martin3 , Z. Galazka2 , M. Albrecht2 , O. Bierwagen1
                        1
                        Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin,
                                                               Germany
                        2
                          Leibniz-Institut für Kristallzüchtung, Max-Born-Str. 2, 12489 Berlin, Germany
                          3
                            Institute of Physical Chemistry, RWTH Aachen University, D-52056 Aachen,
                                                               Germany
                                                   Email: mazzolini@pdi-berlin.de

                        Gallium oxide, in its thermodynamically stable monoclinic crystal structure
                        (β-Ga2 O3 ), is recently attracting large interest in the field of power elec-
                        tronic devices.[1] Nonetheless, the development of gallium oxide is still in
                        its early stage. A deep understanding of the physical mechanisms ruling its
                        functional properties requires fine control of the material growth.
                        In this contribution we discuss the main aspects related to the deposition
                        of Ga2 O3 thin films with molecular beam epitaxy (MBE). In particular, it
                        will be discussed how the presence of the volatile Ga2 O suboxide is ruling
                        the growth kinetics of Ga2 O3 .[2] Moreover, we explain how metal-exchange
                        catalysis[3] can be applied in the MBE deposition of Ga2 O3 employing an
                        additional In-flux; this allows to maximize the growth rate under deposition
                        conditions which were otherwise prohibitive for Ga2 O3 growth (i.e. high
                        deposition temperatures, O-poor/metal-rich conditions). We show how this
                        approach can be successfully applied in (010)-homoepitaxy in order to ob-
                        tain smooth (rms < 0.5 nm) thin films with almost full metal incorporation
                        in metal-rich conditions at high deposition temperatures (T = 900 ◦ C).[4]
                        Finally, an outlook on the future application of metal-exchange catalysis for
                        the MBE homoepitaxy of Ga2 O3 on different surfaces (i.e. (-201), (100),
                        (001)) will be presented.


                            References:
                        [1] S. J. Pearton, et al., Appl. Phys. Rev., 5, 011301 (2018)
                        [2] P. Vogt and O. Bierwagen, Phys. Rev. Mat., 2, 120401, (2018). [3] P.
                        Vogt, et al., Phys. Rev. Lett., 119, 196001, (2017).
                        [4] P. Mazzolini, et al., Appl. Phys. Lett. Mat., 7, 022511, (2019).




18                                                                                                   GraFOx Summer School
P13: Melanie BuddeTu                                                                                  12:30-12.35




                         Growth of the p-type transparent oxides NiO and
                                 SnO by plasma-assisted MBE
                                                      Melanie Budde
                               Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im
                         Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, D-10117 Berlin, Germany
                                                 Email: budde@pdi-berlin.de


                     The focus of my project is the growth of high quality p-type transparent con-
                     ductive oxides (TCO), which started in October 2016 as part of GraFOx. In
                     the first years I grew NiO on different substrates using plasma assisted MBE.
                     Different growth conditions were investigated and a new metrics to define
                     the crystall quality of rocksalt crystal structures using Raman was proposed.
                     [1] Although, good quality material was grown at a substrate temperature
                     of 700 ◦ C, the layers were insulating. An increase in the conductivity and
                     positive Seebeck coefficients, confirming the p-type transport, were observed
                     after an oxygen plasma treatment. Spectroscopy measurements revealed a
                     creation of a surface dipole, leading to a high sheet surface conductance of
                     about 5 µS. Recently, I started to investigate SnO as a possible p-type TCO.
                     However, SnO is a meta-stable material, which can be easily oxidized into
                     the n-type TCO SnO2 and well defined growth conditions are needed.

                     On my poster I would like to show my recent results on the growth of
                     the meta-stable SnO. Therefore different growth experiments were carried
                     out on c-plane Al2 O3 , defining a relation between Sn and oxygen flux to
                     avoid the growth of the stable SnO2 or Sn phase, based on investigations
                     by Vogt et al. [2] In addition, the desorption of SnO was investigated, in-
                     dicating 400 ◦ C as the highest possible growth temperature. Investigations
                     were made using a line-of-sight quadrupole mass spectrometer. Different
                     samples were grown on YSZ(001), giving a better lattice match for SnO, in
                     the found growth window and characterized using a Hall setup and X-ray
                     diffraction. In addition, the effect of post-annealing was investigated on the
                     sample characteristics.

                     [1] Budde et al., J. Appl. Phys. 123, 195301 (2018).
                     [2] Vogt and Bierwagen, Appl. Phys. Lett. 106, 081910 (2015).




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                       19
P14: Andreea Costats                                                                                               Tu 12:35-12:40




                                       Optoelectronic Properties of Heterojunction
                                             ZnO-CuxO Core-Shell Nanowires
                                                          Andreea Costas
                         National Institute of Material Physics, PO Box MG7, 077125, Magurele, Romania
                                                  Email: andreea.costas@infim.ro


                        My work on oxide semiconductors is related to electronic devices like diodes and field effect
            transistors based on semiconducting single nanowires [1, 2]. ZnO and CuO were used in the
            fabrication of the electronic devices were. Thus, ZnO and CuO nanowires arrays were prepared using
            dry and wet methods: thermal oxidation in air of zinc and copper foils and aqueous solution growth.
            The electronic devices based on single nanowires were fabricated employing thin film deposition
            methodes (radio frequency magnetron sputtering and thermal vacuum evaporation) and lithographic
            techniques (photolithography, electron beam lithography and focused ion beam induced deposition).
            The electrical properties revealed field effect transistors and diodes with very good performances:
            ideality factor n= 1.83 and on-off ratios of about 103 for diodes, on-off ratios of about 103 – 105 and
            high mobilities (up to 167 cm2 V-1s-1) for field effect transistors.
                        The Poster presentation will be focused on my current work: preparation, properties and
            photodetector applications of ZnO-CuxO core-shell radial heterojunction nanowire arrays [3]. The
            nanowires were fabricated combining two simple preparation methods: thermal oxidation in air of
            zinc foils and radio frequency magnetron sputtering. Morphological, structural, optical,
            compositional and surface chemistry properties of the obtained ZnO-CuxO core-shell nanowire arrays
            were investigated. Individual ZnO-CuxO core-shell nanowires were contacted using lithographic and
            thin film deposition techniques in order to evaluate their electrical and photoelectrical properties,
            demonstrating a rectifying behaviour. The photocurrent measurements exhibits that these n-p diodes
            based on single ZnO-CuxO core-shell nanowires can be used as photodetectors applications.


            References:
            [1] C. Florica, A. Costas, A. Kuncser, N. Preda, I. Enculescu, High performance FETs based on ZnO
            nanowires synthesized by low cost methods. Nanotechnology 27, 475303 (2016).
            [2] C. Florica, A. Costas, A. G. Boni, R. Negrea, L. Ion, N. Preda, L. Pintilie, I. Enculescu, Electrical
            properties of single CuO nanowires for device fabrication: Diodes and field effect transistors. Appl.
            Phys. Lett. 106, 223501 (2015).
            [3] A. Costas, C. Florica, N. Preda, N. Apostol, A. Kuncser, A. Nitescu, I. Enculescu, Radial
            heterojunction based on single ZnO-CuxO core-shell nanowire for photodetector applications, Scientific
            Reports, manuscript number: SREP-18-40383 under review.




20                                                                                                      GraFOx Summer School
P15: Georg Hoffmann                                                                                   Tu 12:40-12:45




                             SnO source for epitaxial growth of BaSnO3
                                                    Georg Hoffmann
                               Paul-Drude-Institut für Festkörperelektronik Leibniz-Institut im
                        Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, D-10117 Berlin, Germany
                                               Email: hoffmann@pdi-berlin.de


                           In my project, the focus lies on the growth of high quality transparent
                       BaSnO3 /LaInO3 heterostructures within the frame of the BASTET project,
                       a subset of GraFOx, which I joined in May 2018. The heterostructures are
                       planed to be grown by molecular beam epitaxy (MBE). In a first step, in
                       order to ensure highest quality of the future samples, I conducted quadrupol
                       mass spectrometry (QMS) measurements for different SnO sources for the
                       optimized growth of BaSnO3 . As source materials, I compared SnO2 , Sn,
                       and SnO2 +Sn mixtures by determining appearance potentials of the con-
                       stituents of the evaporated flux as well as their activation energies. In ad-
                       dition to that, I also studied the influence of different oxygen background
                       pressures on the evaporation of the elements over a large range of tempera-
                       tures.
                       On my poster, I will show the results of the QMS investigation which reveal
                       the potential of metal + oxide mixtures for higher growth rates at lower cell
                       temperatures. Further, I also would like to point out how the oxygen back-
                       ground in a common plasma assisted MBE system can affect the quality of
                       the evaporated material.




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                          21
P16: Alexandra Papadogianni                                                                                   Tu 12:45-12:50




                           Homoepitaxial Growth of In2 O3 Films by
                         Plasma-Assisted Molecular Beam Epitaxy on
                       (100)-, (110)-, and (111)-oriented bulk substrates
                                                 Alexandra Papadogianni
                               Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im
                                      Forschungsverbund Berlin e.V., Berlin, Germany
                                             Email: papadogianni@pdi-berlin.de


                     Indium oxide In2 O3 is a transparent semiconducting oxide (TSO) exhibit-
                     ing native n-type conductivity referred to as unintentional doping (UID),
                     the origin of which has been attributed to oxygen vacancies and hydrogen
                     impurities acting as shallow donors. In2 O3 is a well-established material
                     in industry in its highly conductive Sn-doped form (ITO) as a transpar-
                     ent contact in optoelectronic devices. Moreover, In2 O3 has been studied
                     for applications as the active material in conductometric gas sensors, which
                     is closely related to the existence of a highly gas-sensitive surface electron
                     accumulation layer (SEAL) observed as a downward band bending at the
                     In2 O3 surface.
                         The aim of the project C2.4 (In1−x Gax )2 O3 -based gas sensors is to under-
                     stand and control the electronic and fundamental gas sensing mechanisms
                     of cubic In2 O3 , as well as the transition behavior towards gallium oxide
                     (Ga2 O3 ) with increasing Ga-content of cubic (In1−x Gax )2 O3 .
                         Several studies on heteroepitaxially grown phase-pure In2 O3 thin films by
                     molecular beam epitaxy (MBE) have been demonstrated on substrates such
                     as a- and c-plane Al2 O3 and ZrO2 :Y (YSZ) with different orientations. On
                     these substrates In2 O3 grows as textured films with rotational domains and
                     as single-crystalline films with dislocations at the interface, due to tensile
                     lattice mismatch, respectively. For most device applications and related
                     studies, such film quality suffices. In order to completely understand the
                     fundamental physical properties of the material, however, the investigation
                     of high-quality homoepitaxially grown films is necessary.
                         This is the first study presenting the growth of high-quality homoepi-
                     taxial In2 O3 films by plasma-assisted molecular beam epitaxy (PA-MBE)
                     on (100)-, (110)-, and (111)-oriented bulk In2 O3 substrates. In-situ and
                     ex-situ surface and crystal structure characterization techniques allow for
                     investigations on the surface stability (self-reorganization, faceting) of the
                     In2 O3 layers grown under oxygen- and indium-rich conditions.




22                                                                                                  GraFOx Summer School
P17: Kyoung-Ho Kim                                                                                   Tu 12:50-12:55




                        A Study on Growth of High-Quality Gallium
                       Oxide Thin Film on A Sapphire Substrate Using
                               A Rear Flow Type Mist CVD
                                                   Kyoung-Ho Kim
                      Energy and Environmental Division, Korea Institute of Ceramic Engineering and
                                       Technology, Jinju 52851, Republic of Korea.
                                               Email: gusooni@gmail.com


                      I graduated from the University of Suwon for B.S. degree in Chemistry and
                      I received a master’s degree in the University of Ajou. In master’s course,
                      the subject of M.S. degree title was “Control of alkali metal stoichiometries
                      via partial substitution of metal ions in quaternary metal phosphates”. I
                      have studied the three-dimensional structure of lithium phosphate oxide that
                      structure of crystals physical properties between the atoms of and angle
                      bonds. Currently, I am in Ph.D. student in the School of Materials Science
                      and Engineering from University of Pusan. The aim of Ph.D. is a growth and
                      analysis of high-quality gallium oxide on sapphire substrate by mist CVD.
                      I am studying to improve the quality of power semiconductor materials.
                      In addition, Other approaches such as alloy, doping, etc. will be further
                      studied.
                          To date, several different types of growth methods have been employed
                      for the heteroepitaxy of Ga2O3 such as physical vapor deposition (PVD),
                      molecular beam epitaxy (MBE), sputtering, pulsed laser deposition (PLD),
                      HVPE, mist CVD and so on. Among these mist CVD is one of fascinat-
                      ing system for growing Ga2O3 thin films due to low cost fabrication. In
                      common, conventional mist CVD utilize carrier gas and dilution gas to con-
                      trol mist flow. However, such gas control components are not necessary
                      if a fan is attached on the rear part of mist CVD system. In this study,
                      we report the growth of α-Ga2O3 epilayers on c-plane sapphire substrates
                      grown by rear-flow-controlled mist-CVD. The grown Ga2O3 epilayers were
                      evaluated by optical and structural characterizations. Additionally, finite
                      element analysis simulations were carried out in order to understand the
                      growth behaviors.




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                         23
P18: Aykut Baki                                                                                            Tu 12:55-13:00




                   Epitaxial growth of SrTiO3 thin films by MOVPE
                   A.Baki, J.Stöver, K.Irmscher, T.Markurt, M.Albrecht, J.Schwarzkopf
                   Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2 - 12489 Berlin, Germany
                                              Email: aykut.baki@ikz-berlin.de


                       SrTiO3 represents a prototype of perovskite materials. It provides a
                   high dielectric constant and a switchable/tunable resistivity, which makes it
                   potentially interesting for resistive switching memories (ReRAM). Addition-
                   ally, promising thermoelectric properties of SrTiO3 are reported. Deposition
                   of SrTiO3 thin films by pulsed laser deposition (PLD) is extensively inves-
                   tigated, however, growth by metal-organic vapor phase epitaxy (MOVPE)
                   is rarely reported yet. MOVPE takes place close to the thermodynamic
                   equilibrium and is therefore expected to provide smooth and low defect thin
                   films.
                   This study is aimed to fundamentally investigate the structural and electri-
                   cal properties of SrTiO3 thin films grown by liquid-delivery spin MOVPE
                   by using the metal-organic precursors Sr(tmdh)2 -tetraglyme and Ti(Oi Pr)2
                   (tmdh)2 solved in dry toluene. Unstrained and compressively strained epi-
                   taxial films are realized by the application of (100) SrTiO3 and (110) DyScO3
                   as oxide substrates. The influence of a wide range of MOVPE growth pa-
                   rameters such as substrate and evaporation temperatures, the Si/Ti ratio
                   in the gas phase and the oxygen partial pressure is studied with regard to
                   phase and (point) defect formation in the films.
                   The structural properties are mainly analyzed by high-resolution X-ray
                   diffraction, transmission electron microscopy, and atomic force microscopy.
                   Furthermore, electrical properties are examined by resistivity and capacitance-
                   voltage measurements.




24                                                                                               GraFOx Summer School
L2: Lena F. Kourkoutis                                                                                     Tu 14:30-16:30




                                Mapping Physical, Chemical and Electronic
                                 Structure of Oxides at the Atomic Scale
                                                      Lena F. Kourkoutis
                          School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA
                                 Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA
                                                Email: lena.f.kourkoutis@cornell.edu


                              Complex transition metal oxides exhibit a rich variety of functional prop-
                          erties including some that are unattainable in conventional semiconductors.
                          Interfaces between these oxides are of particular interest as exotic new phases
                          not found in bulk can be stabilized. In this lecture, I will discuss how sub-
                          atomic electron beams can be used to understand functional properties and
                          emergent phenomena in oxide thin films, heterostructures and multilayers.
                              Today’s aberration-corrected scanning transmission electron microscopes
                          (STEM) routinely focus high-energy electrons down to a spot smaller than
                          1Å in diameter to perform scattering experiments that allow us to study the
                          atomic-scale structure of materials and devices. When combined with elec-
                          tron energy loss spectroscopy (EELS) analysis of the inelastically scattered
                          electrons, these narrow probes can also provide atomic-scale information
                          about the composition and local electronic structure of bulk materials, de-
                          fects and interfaces (Fig. 1) [1, 2]. Using these techniques electronic and
                          structural reconstructions at interfaces, microscopic inhomogeneities and
                          atomic-scale interdiffusion can now readily be characterized and correlated
                          with the macroscopic properties of the structure [3, 4].
                              Most efforts, so far, have focused on room temperature measurements
                          where an imaging resolution of 0.5 Å is achievable. However, a range of
                          materials including complex oxides and their interfaces exhibit exotic func-




                          Figure 1: (left) Atomic-resolution STEM image followed by EELS elemental
                          maps of Ti, La, and Mn acquired simultaneously across an extended defect
                          in a manganite/titanate superlattice film. (right) Two distinct Mn-L com-
                          ponents extracted by multivariate curve resolution. A reduced valence state
                          is observed for Mn atoms that segregate at the defects.




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                               25
L2: Lena F. Kourkoutis                                                                                      Tu 14:30-16:30




                          Figure 2: Aberration-corrected cryo-STEM imaging of a charge-ordered
                          manganite (Bi,Sr,Ca)MnO3 performed at 95K. (right) Overlaid arrows map
                          picometer-scale periodic displacements of atomic columns associated with
                          charge ordering. Area of arrows scales linearly with the magnitude of the
                          displacement.

                          tionalities below room temperature. Correlating the atomic level structure
                          and electronic properties at cryogenic temperatures is therefore an impor-
                          tant step in realizing the goal of understanding and controlling emergent
                          phenomena in these materials. With this goal in mind, we have developed
                          cryo-STEM techniques for atomic-scale mapping of materials at tempera-
                          tures where phase transitions occur. I will discuss recent results on mapping
                          periodic lattice distortions in charge ordered manganites (Fig. 2) [4] and
                          challenges associated with low temperature STEM. [6]

                           [1] D. A. Muller, L. F. Kourkoutis, M. Murfitt, J. H. Song, H. Y. Hwang,
                               J. Silcox, N. Dellby, O. L. Krivanek, Science 319, 1073 (2008).
                           [2] M. Coll et al., Appl. Surf. Science 482, 1 (2019).
                           [3] L. F. Kourkoutis, J. H. Song, H. Y. Hwang, D. A. Muller, Proc. Natl.
                               Acad. Sci. 107, 11682 (2010).
                           [4] J. Mundy, Y. Hikita, T. Hidaka, T. Yajima, T. Higuchi, H. Y. Hwang,
                               D. A. Muller, L. F. Kourkoutis, Nat. Commun. 5, 3464 (2014).
                           [5] I. E. Baggari, B. H. Savitzky, A. S. Admasu, J. Kim, S.-W. Cheong, R.
                               Hovden, L. F. Kourkoutis, PNAS 115, 1445 (2018).
                           [6] Support by PARADIM, a National Science Foundation Materials In-
                               novation Platform (Grant DMR-1539918), by the Air Force Office of
                               Scientific Research (Award FA 9550-16-1-0305) and the Packard Foun-
                               dation are acknowledged.




26                                                                                                GraFOx Summer School
T21: Tobias Schulz                                                                                     Tu 17:00-17:30




                       Atomic defects in oxide crystals studied by TEM
                                                     Tobias Schulz
                                           Leibniz-Institute for Crystal Growth
                                            Email: tobias.schulz@ikz-berlin.de


                          SrTiO3 is a prototypical material in the emerging field of oxide elec-
                      tronics and in the past years a number of unique devices based on SrTiO3
                      have been proposed: Most prominent among them are such making use of
                      two-dimensional electron gases at the interface between LaAlO3 and SrTiO3
                      and memristive devices that store information in form of tunable resistiv-
                      ity. However, the level of material perfection and its control in SrTiO3 thin
                      films and bulk crystals is by far lower compared to conventional semicon-
                      ductors. This applies in particular to intrinsic atomic defects like oxygen
                      (VO ) and metal vacancies (VTi or VSr ). Although a number of ab-initio
                      studies address the topic of intrinsic atomic defects in SrTiO3, though with
                      contradictory results, little is known about the dynamics of point defect in-
                      cluding formation, diffusion and clustering. To shed light into this topic we
                      grew homoepitaxial thin films of SrTiO3 by pulsed laser deposition with a
                      systematic variation of growth parameters and analyzed formation, diffusion
                      and clustering of point defects by means of transmission electron microscopy
                      (TEM). Figure 1(a) shows a high resolution TEM image of a SrTiO3 layer
                      grown at 600 DegC and a chamber pressure of 10−5 mbar, recorded in a
                      series of 30 images using identical conditions. From such an image series,
                      the vertical lattice parameters can be measured in real space, resulting in
                      the color coded image displayed in 1(b). As can be seen, the locally mea-
                      sured lattice parameter shows local deviations, which are larger than in the
                      underlying bulk material, pointing to the presence of defects, acting as local
                      stressors. Due to the absence of extended defects, we related these local
                      stressors to point defects or point defect clusters. Figure 1(c), displays the
                      standard deviation of the measured vertical lattice parameter from image
                      to image withing the series. Large standard deviation point to a change of
                      the material as a result of its interaction with the electron beam. Obviously,
                      the PLD grown layer has a much stronger interaction with the beam, as
                      compared to the underlying substrate. This indicates that, the presence of
                      point defects destabilize the material under electron beam irradiation via
                      e.g. migration of point defects.




                      Figure 1: High resolution TEM image of a SrTiO3 film grown at 600 DegC
                      and a chamber pressure of 10−5 mbar (with oxygen flow) by PLD on a
                      SrTiO3 substrate. Arrows indicate the film/substrate interface. (b) Color
                      coded map of the vertical lattice parameter revealing local lattice distortions
                      in the film not present in the substrate. (c) Color coded standard deviation
                      of the determined position of atomic columns within a HRTEM image series
                      consisting of 30 images (recorded under identical imaging conditions) show-
                      ing an increase of temporal lattice fluctuations in the film. (b) and (c) are
                      obtained by analyzing the HRTEM image (a).




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                           27
P22: Marian Cosmin Istrate                                                                               Tu 17:30-17:35




                              Study of Crystalline Phases by TEM/HRTEM
                              Techniques in Ferroelectric Oxides Thin Films
                                             Based on HZO
                                                  Marian Cosmin Istrate
                                  National Institute of Materials Physics, Magurele, Romania
                                                 Email:cosmin.istrate@infim.ro


                          For decades the ferroelectric materials were used in many applications
                      such as digital information storage, sensors, pyroelectric energy conversion,
                      etc. Nowadays, the applications demand an understanding of the morpho-
                      logical, structural and compositional properties of the materials down to
                      nanometric and atomic scale. The quality of the deposited thin films as well
                      as the interfaces between them and the substrate plays a key role in the elec-
                      trical behavior (polarization hysteresis loops, C-V and I-V characteristics).
                      A special interest is the study of the dielectric constant, which in the case
                      of these materials can be very huge.

                          Transmission electron microscopy (TEM) is able to provide a complete
                      characterization of the morphological and structural properties of the fer-
                      roelectric oxides. The studied samples consist in thin films of Hf0.5 Zr0.5 O2
                      (HZO) deposited on an IrO electrode and the latter was deposited on a Si
                      (100) substrate with a native SiO2 layer. We study these oxide because
                      lately was discovered that there are some crystalline phases which exhibit
                      ferroelectric properties, especially the orthorhombic phase. The thin films
                      were grown by atomic layer deposition (ALD) using TEMAHf and ZyALD
                      precursors deposited at 300◦ C. In this work we use a Cs probe-corrected
                      JEM ARM 200F electron microscope, TEM-SAED and HRTEM techniques
                      to put in evidence the crystalline phase of the HZO thin film and to inves-
                      tigate the morphological structure of the thin films.




28                                                                                             GraFOx Summer School
P23: Vincenzo Montedoro                                                                               Tu 17:35-17:40




                     Cathodoluminescence of undoped and Si-doped
                                   ε − Ga2 O3 films
                                                  Vincenzo Montedoro
                   Dept. of Mathematical, Physical and Computer Sciences, University of Parma,
                                  Viale delle Scienze 7/A, 43124 Parma, Italy
                                  Email: vincenzo.montedoro@studenti.unipr.it



                                                          Abstract
                           Among the wide band gap semiconductors Gallium Oxide (Ga2 O3 )
                           is one of the most studied in view of its demonstrated applications
                           as: UV photodetectors, transparent electrodes, field-effect transistors,
                           gas sensors and power devices. Moreover, its wide availability, the low
                           cost and the possibility of obtaining it through multiple synthesis paths
                           make this material one of the most interesting wide band gap semicon-
                           ductors. There are several polymorphs of gallium oxide (α, β, ε, δ , γ),
                           among them, the β-polytype is the only one thermodynamically stable .
                           However, other crystal phases also have interesting physical properties,
                           as well as higher crystallographic symmetry, which makes them worth
                           of investigation. We are dealing with the growth and characterization
                           of ε-phase Ga2 O3 (Eg =4,6eV) thin films, either undoped or Si-doped.
                           Heteroepitaxial Gallium Oxide was grown on Al2 O3 substrates, in a
                           MOCVD reactor, at temperatures below the threshold for phase tran-
                           sition. We have carried out optical and electrical characterization.
                           In particular, we present here the results obtained by Cathodolumi-
                           nescence (CL) measurements on undoped and Si-doped samples, with
                           different Si concentrations. These measurements were carried out at
                           different e-beam energies (3-30 KeV), in order to optimize the exper-
                           imental conditions. The CL spectra presented a broad visible band,
                           consisting of at least three subbands peaking at 420nm, 450nm and
                           510nm, and an UV band peaking at 330nm. These bands were re-
                           ported also in the case of β − Ga2 O3 , and suggested to be associated
                           to deep level transitions and a self-trapped exciton respectively. We
                           shall discuss here the role that Si doping plays on the balance between
                           the visible and the UV band. Furthermore, temperature dependent
                           measurements show a progressive enhancement of the UV emission at
                           the expense of the visible emission with increasing temperature. A
                           tentative mechanism accounting for such behavior is proposed. This is
                           the first extensive CL investigation of defects in Si-doped ε − Ga2 O3
                           films . Noticeably, this material exhibited a behavior similar to that
                           reported for β − Ga2 O3 .




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                          29
P24: Lukas Zeinar                                                                                         Tu 17:40-17:45




                      Stoichiometry Engineering Of All-Oxide Epitaxial
                           Ferroelectric Varactors By Pulsed Laser
                                      Deposition (PLD)
                                                     Lukas Zeinar
                            Institute for Materials Science, Technische Universität Darmstadt
                                           Email: zeinar@oxide.tu-darmstadt.de


                         We present all-oxide ferroelectric varactors using low-resistive SrMoO3
                     oxide bottom electrode with the functional ferroelectric Bax Sr1−x TiO3 (BST)
                     grown by pulsed laser deposition (PLD). High quality BST leads to low
                     losses and high quality factors Q of the varactors. Tunability and quality of
                     BST are mainly influenced by (Ba+Sr)/Ti ratio, while the leakage current
                     is mainly affected by the oxygen content.
                         Thermodynamics open a growth window for highly conducting SMO
                     (30 µΩcm) [1] and high quality, high tunable BST. Therefore, growth tem-
                     perature, background atmosphere pressure and flow are scaled to investigate
                     this window and see the influence of the background gas pressure onto the
                     barium to strontium ratio measured by XPS and XRD. The electrical perfor-
                     mance in dependence on growth parameters and stoichiometry respectively
                     and is analyzed by electrical measurements.

                        [1] A. Radetinac et al., Highly conducting SrMoO3 thin films for mi-
                     crowave applications, Appl. Phys. Lett. 105, 114108 (2014).




30                                                                                              GraFOx Summer School
P25: Patrick Salg                                                                                    Tu 17:45-17:50




                          Interface Engineering Of All-Oxide Epitaxial
                                     Ferroelectric Varactors
                                                     Patrick Salg
                            Institute for Materials Science, Technische Universität Darmstadt
                                           Email: salg@oxide.tu-darmstadt.de


                         I am working on all-oxide ferroelectric varactors using a bottom electrode
                     of the highly conducting perovskite SrMoO3 with a room-temperature resis-
                     tivity of 30 µΩcm [1]. Thin-film epitaxial heterostructures of SrMoO3 and
                     the tunable dielectric Ba0.5 Sr0.5 TiO3 were grown by pulsed laser deposition
                     and covered by Au/Pt top electrodes patterned by ion beam etching.
                         Thermodynamics dictate reductive growth conditions for SrMoO3 which
                     is in contrast to the oxygen background pressure during the Bax Sr1−x TiO3
                     growth. An interlayer between SrMoO3 and Bax Sr1−x TiO3 was used to
                     combine these two contradictory growth conditions and prevent the SrMoO3
                     from oxidizing during the Bax Sr1−x TiO3 growth. The effect of different in-
                     terlayer materials as oxygen barrier was investigated by XRD and XPS. This
                     interlayer allows functional all-oxide varactors with a tunability of almost
                     60% at battery voltage level of 3.7 V. Combined with high quality factors of
                     76 at 1 GHz and 55 at 2.7 GHz all-oxide ferroelectric varactors have a high
                     potential for microwave applications.
                         To push this all-oxide technology further towards industrial interest suc-
                     cessful growth studies have been done to grow the heterostructure on a
                     cheaper, industrial popular substrates such as silicon and sapphire.

                        [1] A. Radetinac et al., Highly conducting SrMoO3 thin films for mi-
                     crowave applications, Appl. Phys. Lett. 105, 114108 (2014).




Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts                                         31
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