The electrical conductivity of cubic (In$_{1-x}$Ga$_x$)$_2$O$_3$ films ($x\le0.18$): Native point defects, Sn-doping, and the surface electron accumulation layer

TL;DR

This study explores how alloying In2O3 with Ga affects electrical conductivity, native defects, and surface electron layers, revealing increased electron density and potential for transparent conductive applications.

Contribution

It provides new insights into the effects of Ga alloying on defect chemistry and surface properties of (InGa)2O3 thin films, including the role of native defects and surface accumulation layers.

Findings

Ga alloying increases electron density via native defects

Surface electron accumulation persists up to x=0.18

Sn-doped (InGa)2O3) films show potential as transparent conductors

Abstract

The alloying of the group-III transparent semiconducting sesquioxides In$_2$O$_3$ and Ga$_2$O$_3$ can lead to a modulation of the properties of the parent compounds, e.g., the shallow- and deep-donor character of the oxygen vacancy or the presence and absence of a surface electron accumulation layer, respectively. In this work, we investigate the effect of alloying on the electron transport properties of unintentionally-doped single-crystalline and textured bixbyite (In$_{1-x}$Ga$_x$)$_2$O$_3$ thin films annealed in oxygen and vacuum with Ga contents up to $x$=0.18. Hall effect measurements demonstrate a surprising increase in electron density due to native defects with added Ga. This increase may be related to the incorporation of Ga-interstitials or oxygen vacancies induced by Ga-related unit-cell distortions. A combined investigation based on hard and soft x-ray photoelectron spectroscopy measurements demonstrates the existence of the surface electron accumulation layer for all alloy films and, hence, no depletion up to $x$=0.18. Finally, we additionally demonstrate a single-crystalline (In$_{0.92}$Ga$_{0.08}$)$_2$O$_3$:Sn film, as a possible transparent conductive oxide with a wider band gap than that of (Sn-doped) In$_2$O$_3$.