PROGRAM & ABSTRACTS GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices - TU Berlin
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
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 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
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
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
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
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
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 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 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 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 SchoolSummer 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 13L1: 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 SchoolL1: 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 15L1: 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 SchoolT11: 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 17T12: 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 SchoolP13: 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 19P14: 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 SchoolP15: 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 21P16: 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 SchoolP17: 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 23P18: 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 SchoolL2: 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 25L2: 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 SchoolT21: 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 27P22: 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 SchoolP23: 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 29P24: 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 SchoolP25: 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 31You can also read
