Kinetics versus thermodynamics of the metal incorporation in molecular beam epitaxy of (InxGa1-x)2O3

We present a detailed study of the reaction kinetics and thermodynamics of the plasma-assisted oxide molecular beam epitaxy of the ternary compound (InxGa1-x)(2)O-3 for 0 <= x <= 1. We measured the growth rate of the alloy in situ by laser reflectrometry as a function of growth temperature T-G for different metal-to-oxygen flux ratios r(Me), and nominal In concentrations x(nom) in the metal flux. We determined ex situ the In and Ga concentrations in the grown film by energy dispersive X-ray spectroscopy. The measured In concentration x shows a strong dependence on the growth parameters T-G, r(Me), and x(nom) whereas growth on different co-loaded substrates shows that in the macroscopic regime of similar to mu m(3) x does neither depend on the detailed layer crystallinity nor on crystal orientation. The data unveil that, in presence of In, Ga incorporation is kinetically limited by Ga2O desorption the same way as during Ga2O3 growth. In contrast, In incorporation during ternary growth is thermodynamically suppressed by the presence of Ga due to stronger Ga-O bonds. Our experiments revealed that Ga adatoms decompose/etch the In-O bonds whereas In adatoms do not decompose/etch the Ga-O bonds. This result is supported by our thermochemical calculations. In addition we found that a low TG and/or excessively low rMe kinetically enables In incorporation into (InxGa1-x)(2)O-3. This study may help growing high-quality ternary compounds (InxGa1-x)(2)O-3 allowing band gap engineering over the range of 2.7-4.7 eV. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.