Variable‐Range Hopping Conduction in Amorphous, Non‐Stoichiometric Gallium Oxide

Advanced Electronic Materials, vol. 11

Abstract

Abstract Amorphous, non‐stoichiometric gallium oxide (a‐GaO x , x < 1.5) is a promising material for many electronic devices, such as resistive switching memories, neuromorphic circuits and photodetectors. So far, all respective measurements are interpreted with the explicit or implicit assumption of n‐type band transport above the conduction band mobility edge. In this study, the experimental and theoretical results consistently show for the first time that for an O/Ga ratio x of 0.8 to 1.0 the dominating electron transport mechanism is, however, variable‐range hopping (VRH) between localized states, even at room temperature and above. The measured conductivity exhibits the characteristic exponential temperature dependence on T −1/4 , in remarkable agreement with Mott's iconic law for VRH. Localized states near the Fermi level are confirmed by photoelectron spectroscopy and density of states (DOS) calculations. The experimental conductivity data is reproduced quantitatively by kinetic Monte Carlo (KMC) simulations of the VRH mechanism, based on the ab‐initio DOS. High electric field strengths F cause elevated electron temperatures and an exponential increase of the conductivity with F 1/2 . Novel results concerning surface oxidation, magnetoresistance, Hall effect, thermopower and electron diffusion are also reported. The findings lead to a new understanding of a‐GaO x devices, also with regard to metal|a‐GaO x Schottky barriers.

Authors 7

1. Tobias Romstadt Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry RWTH Aachen University 52074 Aachen Germany

   Institute of Physical Chemistry, RWTH Aachen University, 52074 Aachen, Germany

2. Fabian M. Draber Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry RWTH Aachen University 52074 Aachen Germany

   Institute of Physical Chemistry, RWTH Aachen University, 52074 Aachen, Germany

3. Jinseok Ryu

   Seoul National University

   Affiliation as printed

   Department of Materials Science and Engineering Seoul National University Seoul 08826 Republic of Korea

   Department of Materials Science and Engineering, Seoul National University, Seoul, 08826 Republic of Korea

4. Thorben Böger Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry RWTH Aachen University 52074 Aachen Germany

   Institute of Physical Chemistry, RWTH Aachen University, 52074 Aachen, Germany

5. Andreas Falkenstein Aachen Institute of Physical Chemistry

   RWTH Aachen University

   Affiliation as printed

   Institute of Physical Chemistry RWTH Aachen University 52074 Aachen Germany

   Institute of Physical Chemistry, RWTH Aachen University, 52074 Aachen, Germany

6. Miyoung Kim

   Seoul National University

   Affiliation as printed

   Department of Materials Science and Engineering Seoul National University Seoul 08826 Republic of Korea

   Department of Materials Science and Engineering, Seoul National University, Seoul, 08826 Republic of Korea

7. Manfred Martin corresponding Aachen Institute of Physical Chemistry

   Seoul National University · RWTH Aachen University

   Affiliation as printed

   Department of Materials Science and Engineering Seoul National University Seoul 08826 Republic of Korea

   Institute of Physical Chemistry RWTH Aachen University 52074 Aachen Germany

   Department of Materials Science and Engineering, Seoul National University, Seoul, 08826 Republic of Korea

   Institute of Physical Chemistry, RWTH Aachen University, 52074 Aachen, Germany