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

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

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

PROGRAM & ABSTRACTS 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

2 GraFOx Summer School 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

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

Welcome Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 3 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 GraFOx Summer School on Oxide Semiconductors for Smart Electronic Devices

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

4 GraFOx Summer School Program Time / Day Monday 3.6. Tuesday 4.6. Wednesday 5.6. Thursday 6.6. 08:00-09:00 Arrival 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 T11: Oliver Bierwagen T31: Susi Lindner T41: Feljin Jose 11:45-11:50 P42: Nicoleta G. Apostol 11:50-11:55 P43: Ioana Lalau 11:55-12:00 P44: Anatoly Kozlov 12:00-12:05 T12: Piero Mazzolini T32: Celina Schulze P45: Hannah Morgan-Cooper 12:05-12:15 P49: Poster Viewing 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 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 EII: Boat Trip L5: Roberto Fornari 15:30-16:30 Shuttle bus transfer from MXP 16:30-17:00 Coffee & poster session Coffee & poster session 17:00-17:05 T21: Tobias Schulz P51: Jacopo Remondina 17:05-17:10 P52: Nazir Jaber 17:10-17:15 P53: Carmine Borelli 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 Check-in & Registration P22: Marian Cosmin Istrate L6: Michael Heuken 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 17:55-18:00 P27: Alexander Karg 18:00-18:15 EI: German Culture and History 18:15-18:30 18:30-19:00 19:00-19:30 19:30-21:30 Aperitivo di Benvenuto Dinner Dinner on your own Dinner Program

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

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 5 Program Friday 7.6. Saturday 8.6. Sunday 9.6. Time / Day Breakfast 08:00-09:00 L7: Chris van de Walle L8: Debdeep Jena Checkout and Bus Transfer to MXP 09:00-09:05 09:10-11:00 Coffee and Posters 11:00-11:30 T71: Konstantin Lion T81: Christian Golz Departure 11:30-11:45 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 P79: Poster Viewing P85: Taylor Moule 12:00-12:05 P89: Poster Viewing 12:05-12:15 12:15-12:30 12:30-12:35 12:35:12:40 12:40-12:45 12:45-12:50 12:50-12:55 12:55-13:00 Lunch 13:00-14:30 EIII: City Tour L9: Regina Dittmann 14:30-15:30 15:30-16:30 Coffee & poster session 16:30-17:00 T91: Roxana-Elena Patru 17:00-17:05 17:05-17:10 17:10-17:15 17:15-17:20 17:20-17:25 17:25-17:30 T92: Neculai Plugaru 17:30-17:35 17:35-17:40 17:40-17:45 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 Poster removal 18:30-19:00 19:00-19:30 Dinner on your own Dinner 19:30-21:30

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

Speakers Thefollowing highlyrecognized researchers inthe field ofoxide ­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 Speakers 6 GraFOx Summer School

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

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 Social Activities Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts

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

8 GraFOx Summer School 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.

Program Committeee

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

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 9 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.

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

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GraFOx Summer School 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.

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

Program & Abstracts 12 GraFOx Summer School

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts

13 Abstracts Tuesday, 4 June 2019 Session 1: Chair: Henning Riechert L1: Shizuo Fujita � 14 T11: Oliver Bierwagen � 17 T12: Piero Mazzolini � 18 P13: Melanie Budde � 19 P14: Andreea Costats � 20 P15: Georg Hoffmann � 21 P16: Alexandra Papadogianni � 22 P17: Kyoung-Ho Kim � 23 P18: Aykut Baki � 24 Session 2: Chair: Martin Albrecht L2: Lena F. Kourkoutis � 25 T21: Tobias Schulz � 27 P22: Marian Cosmin Istrate � 28 P23: Vincenzo Montedoro � 29 P24: Lukas Zeinar � 30 P25: Patrick Salg � 31 P26: Cristian Radu � 32 P27: Alexander Karg � 33 Wednesday, 5 June 2019 Session 3: Chair: Piero Mazzolini L3: Claudine Noguera � 34 T31: Susi Lindner � 36 T32: Celina Seraphin Schulze � 37 T33: Felix Reichmann � 38 P34: Johannes Feldl � 39 P35: Elena Maznitsyna � 40 P36: Marie Bischoff � 41 P37: Chiara Groppi � 42 P38: Melania Loredana Onea � 43 P39: Ovidiu Cojocaru � 44 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 Session 5: Chair: Melanie Budde/Julian Stöver L5: Roberto Fornari � 51 P51: Jacopo Remondina � 53 P52: Nazir Jaber � 55 P53: Carmine Borelli � 56 P54: Philipp John � 57 P55: Emroj Hossain � 58 P56: Maneesha Narayanan � 59 Session 6: Chair Holger Eisele L6: Michael Heuken � 60 Friday, 7 June 2019 Session 7: Chair: Susi Lindner L 7: Chris van de Walle � 63 T71: Konstantin Lion � 64 P72: Sebastian Tillack � 65 P73: Joe Willis � 66 Saturday, 8 June 2019 Session 8: Chair: Nicoleta G Apostol L8 Debdeep Jena � 67 T81: Christian Golz � 69 P82: Martina Zupancic � 70 P83: Robin Ahrling � 71 P84: Johannes Boy � 72 P85: Taylor Moule � 73 Session 9: Chair: Oliver Bierwagen L9: Regina Dittmann � 74 T91: Roxana-Elena Patru � 75 T92: Neculai Plugaru � 76 T93: Julian Stöver � 77 Abstracts

14 GraFOx Summer School 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 (N2O) 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 Ga2O3 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-Ga2O3, fol- lowed by n-type doing, band gap tuning by α-(Al,Ga)2O3 and α-(In,Ga)2O3 alloys, and formation of heterostructures [1]. FLOSFIA Inc. developed α- Ga2O3 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-Ga2O3 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-Ga2O3 power devices, therefore, may be accepted even for home appliances in which SiC and GaN devices are hardly used due

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 15 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 Mg0.92Zn0.08O 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 Mg0.95Zn0.05O 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).

16 GraFOx Summer School L1: Shizuo Fujita Tu 09:15-11:00 2 3 4 5 6 7 (d)#4 (x=0.74) (c)#3 (x=0.81) (b)#2 (x=0.92) 300K (x50) 300K (x50) 300K (x25) 300K (x50) 6K 6K 6K 6K (a)#1 (x=0.95) 600 400 200 Wavelength [nm] Photon Energy [eV] CL Intensity [a.u.] substrate exhaust carrier gas (N2 or O2) flow meter source solution water ultrasonic transducer heater quartz tube flow meter mist 1.9 2 2.1 2.2 4 5 6 7 8 9 5 5.5 Averaged Bond Length [Å] Band Gap [eV] a-axis Lattice Constant [Å] 4.7 α-Al2O3 α-In2O3 α-Ga2O3 α-(Al,Ga)2O3 α-(In,Ga)2O3 Fig.

4. An AFM surface image of the Mg.92Zn0.08O film. Fig. 5. CL spectra of MgxZn1-xO film of different x at the temperatures of 6 and 300 K. Fig. 3. Cross sectional TEM and SEM images of a Ga2O3 layer on sapphire with SiO2 masks fabricated by epitaxial layer overgrowth (ELO). Fig. 2. Bandgaps of α-(Al,Ga)2O3 and α-(In,Ga)2O3 alloys.

Fig. 1. An example of system configurations of mist CVD equipment.

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 17 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”.

18 GraFOx Summer School T12: Piero Mazzolini Tu 12:00-12:30 Growth and Characterization of Epitaxial Ga2O3 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-Ga2O3), 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 Ga2O3 thin films with molecular beam epitaxy (MBE).

In particular, it will be discussed how the presence of the volatile Ga2O suboxide is ruling the growth kinetics of Ga2O3.[2] Moreover, we explain how metal-exchange catalysis[3] can be applied in the MBE deposition of Ga2O3 employing an additional In-flux; this allows to maximize the growth rate under deposition conditions which were otherwise prohibitive for Ga2O3 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 Ga2O3 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).

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 19 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 Al2O3, 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).

20 GraFOx Summer School 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-1 s-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.

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 21 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.

22 GraFOx Summer School P16: Alexandra Papadogianni Tu 12:45-12:50 Homoepitaxial Growth of In2O3 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 In2O3 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.

In2O3 is a well-established material in industry in its highly conductive Sn-doped form (ITO) as a transpar- ent contact in optoelectronic devices. Moreover, In2O3 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 In2O3 surface.

The aim of the project C2.4 (In1−xGax)2O3-based gas sensors is to under- stand and control the electronic and fundamental gas sensing mechanisms of cubic In2O3, as well as the transition behavior towards gallium oxide (Ga2O3) with increasing Ga-content of cubic (In1−xGax)2O3. Several studies on heteroepitaxially grown phase-pure In2O3 thin films by molecular beam epitaxy (MBE) have been demonstrated on substrates such as a- and c-plane Al2O3 and ZrO2:Y (YSZ) with different orientations. On these substrates In2O3 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 In2O3 films by plasma-assisted molecular beam epitaxy (PA-MBE) on (100)-, (110)-, and (111)-oriented bulk In2O3 substrates. In-situ and ex-situ surface and crystal structure characterization techniques allow for investigations on the surface stability (self-reorganization, faceting) of the In2O3 layers grown under oxygen- and indium-rich conditions.

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 23 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.

24 GraFOx Summer School 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(OiPr)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.

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 25 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.

26 GraFOx Summer School 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.

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 27 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).

28 GraFOx Summer School 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 Hf0.5Zr0.5O2 (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.

Oxide Semiconductors for Smart Electronic Devices – Program & Abstracts 29 P23: Vincenzo Montedoro Tu 17:35-17:40 Cathodoluminescence of undoped and Si-doped ε − Ga2O3 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 (Ga2O3) 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 Ga2O3 (Eg=4,6eV) thin films, either undoped or Si-doped.

Heteroepitaxial Gallium Oxide was grown on Al2O3 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 − Ga2O3, 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 − Ga2O3 films . Noticeably, this material exhibited a behavior similar to that reported for β − Ga2O3.

30 GraFOx Summer School 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 BaxSr1−xTiO3 (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).

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