Semiconducting Oxides

Oxides are among the materials with the widest tunability of physical properties. Spanning insulators, semiconductors, metallic conductors and superconductors, magnetic materials, ferro-/antiferro- and other dielectrics, oxides are a materials class with high potential for a new generation of electronic devices for energy and sensing applications.

Traditionally, oxides have been synthesized by pulsed laser deposition or sputtering, which both have drawbacks in terms of material quality. A higher material quality can be achieved by molecular beam epitaxy (MBE), which is the growth method used by us.

Our research aims at exploring the properties of semiconducting oxides at the materials limit, equally taking into account the understanding of the growth thermodynamics and kinetics as well as the materials application perspective. Providing samples for (international) collaborations is an important part of our scientific culture. To date, our materials portfolio comprises the n-type oxides (Ga,In,Al)₂O₃, SnO₂, the perovskites BaSnO₃ and LaInO₃, as well as the p-type oxides SnO and (the antiferromagnet) NiO. Out of these SnO₂, NiO, and In₂O₃ are frequently used in conductometric gas sensing—an application whose fundamental investigation together with external collaborators greatly benefits from our well-defined samples. Energy-efficient power electronics as well as solar-blind UV sensing are further important applications, both of which are foreseen to profit tremendously from the ultra-wide bandgap semiconductor Ga₂O₃ and its solid solutions with In₂O₃ and Al₂O₃. For the same purpose, we recently started investigating rutile-GeO₂ and its solid solutions with SnO₂ and SiO_2.

Embedded in the Berlin-based Leibniz ScienceCampus Growth and fundamentals of oxides for electronic applications (GraFOx), led by PDI, our activities are currently divided into the following projects:

• Metastable III₂O₃ alloys, deep acceptor-doping, and p-type oxides
• MBE of LaInO₃/BaSnO₃ heterostructures for electronic applications (funding in Leibniz competition “BaSnO₃-based heterostructures for electronic applications”)
• Point defects control in Ga₂O₃ thin films grown via molecular beam epitaxy (funded by DFG)
• (Si,Ge,Sn)O₂-based ultra-wide bandgap semiconductors for power electronics (funding in Leibniz competition)

Author: K. Tetzner , K. O. Egbo , M. Klupsch , R.-S. Unger , A. Popp , T.-S. Chou , S. Bin Anooz , Z. Galazka , A. Trampert , O. Bierwagen , J Würfl
Title: SnO/β-Ga2O3 heterojunction field-effect transistors and vertical p-n diodes
Source: Appl. Phys. Lett. , 120 , 112110 ( 2022 )
DOI: 10.1063/5.0083032

Author: J. Feldl , M. Feneberg , A. Papadogianni , J. Lähnemann , T. Nagata , O. Bierwagen , R. Goldhahn , M. Ramsteiner
Title: Band gap widening and phonon behavior of cubic single-crystalline (In,Ga)2O3 alloy films
Source: Appl. Phys. Lett. , 119 , 042101 ( 2021 )
DOI: 10.1063/5.0056532

Author: O. Bierwagen , P. Vogt , P. Mazzolini
Title: Gallium Oxide - Plasma-Assisted Molecular Beam Epitaxy 2—Fundamentals of Suboxide-Related Growth Kinetics, Thermodynamics, Catalysis, Polymorphs, and Faceting
Source: Springer Series in Materials Science , 293 , 95 ( 2020 )
DOI: 10.1007/978-3-030-37153-1_6

Author: G. Hoffmann , M. Budde , P. Mazzolini , O. Bierwagen
Title: Efficient suboxide sources in oxide molecular beam epitaxy using mixed metal + oxide charges: The examples of SnO and Ga2O
Source: APL Mater. , 8 , 031110 ( 2020 )
DOI: 10.1063/1.5134444 

Author: J. Rombach , A. Papadogianni , M. Mischo , V. Cimalla , L. Kirste , O. Ambacher , T. Berthold , S. Krischok , M. Himmerlich , Sören Selve , O. Bierwagen
Title: The role of surface electron accumulation and bulk doping for gas-sensing explored with single-crystalline In2O3 thin films
Source: Sens. Actuators B Chem. , 236 , 909 ( 2016 )
DOI: 10.1016/j.snb.2016.03.079