Anisotropic strain relaxation in epitaxially constrained α -(Al,Ga)2O3 thin films on a-plane Al2O3

Abstract

Binary α-Ga2O3 and ternary α-(AlxGa1−x)2O3 thin films with x = 0.29 and 0.54 were deposited on a-plane Al2O3 substrates via plasma-assisted molecular beam epitaxy. The strain relaxation dynamics along three orthogonal crystal directions was investigated ex situ and in situ by synchrotron-based high-resolution x-ray diffraction. A pronounced in-plane anisotropy was observed as strain is preferably built up across [1¯1.0] whereas along [00.1] it is effectively relieved. The particular behavior depends on the Al content with almost immediate plastic relaxation for x = 0 and 0.29. For x = 0.54, strain relaxation is elastic within the first monolayers. A dislocation glide on the r-plane slip system has been identified as the dominating plastic relaxation mechanism as layers grow thicker.