Spontaneous Donor Defects and Voltage-Assisted Hole Doping in Beta-Gallium Oxides under Multiple Epitaxy Conditions

TL;DR

This study uses first-principles computations to analyze spontaneous donor defects in beta-Ga2O3 grown by various techniques and demonstrates voltage-assisted hole doping to improve p-type conductivity.

Contribution

It identifies growth technique-dependent donor defects and proposes a voltage-assisted doping method to reduce donors and enhance hole concentration in beta-Ga2O3.

Findings

Different primary donor defects for each growth method.

Voltage-assisted doping significantly reduces donor levels.

Achieved high hole concentration without external dopants.

Abstract

Beta-phase gallium oxide (beta-Ga2O3) is prone to the spontaneous formation of donor defects but poses a formidable challenge in achieving high-quality p-type doping, mainly due to its exceptionally low valence band maximum (VBM). In this study, we utilize first-principles computations to investigate the origin of spontaneous donor defects in beta-Ga2O3 grown by three typical techniques: molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), and halide vapor phase epitaxy (HVPE). Our findings elucidate that the primary donor defects vary with the growth techniques, specifically Gai3+ for MBE, Hi+ and CGa+ for MOCVD, and (2VGa+Gai+2VO)+ and ClO+ for HVPE under unintentionally doped conditions. Employing a theoretically proposed voltage-assisted doping method, we computationally demonstrate that the dominant spontaneous donors can be significantly reduced accompanied by a noticeable increase in acceptors, leading to a stepwise reduction of Fermi level to 0.52, 0.88, and 2.10 eV above VBM for the MOCVD, HVPE, and MBE methods, and a hole concentration of 8.5*10^17, 8.7*10^11, and 2.7*10^-9 cm-3, respectively, at room temperature without the use of external dopants. By introducing Mg doping, we further reduce the Fermi level for both the MBE and HVPE experiments.