Strain Relaxation in Α-(Alxga1-X)2o3 Thin Films Grown on M-Plane and R-Plane Sapphire Via Metalorganic Chemical Vapor Deposition

Abstract

The growing interest in gallium oxide (Ga2O3) as an ultrawide bandgap semiconductor stems from its potential for high-efficiency power electronics and solar-blind ultraviolet photodetectors. However, realizing single-crystalline α-(AlxGa1−x)2O3 with multilayer structures suitable for device applications remains challenging. This study establishes a quantitative framework for strain relaxation in corundum α-(AlxGa1−x)2O3 thin films grown on nonpolar m-plane and semi-polar r-plane sapphire via metalorganic chemical vapor deposition (MOCVD), integrating experimental and first-principles approaches. High-quality α-(AlxGa1−x)2O3 films with aluminum content ranging from 0.45 to 0.94 were synthesized through optimized growth parameters, achieving an exceptionally low full width at half maximum (FWHM) of ~0.1° for compositions up to 83% Al. Reciprocal space mapping (RSM) and density functional theory (DFT) reveal a composition-dependent critical thickness variation: films with x < 0.6 exhibit complete or partial relaxation at 100 nm, whereas those with x ≥ 0.6 maintain pseudomorphic coherence (m-plane) or undergo phase separation (r-plane). Notably, substrate orientation governs strain evolution, with m-plane films experiencing progressive out-of-plane strain accumulation, while r-plane films retain higher in-plane strain, inducing structural instability for x < 0.7. First-principles elastic constants and lattice parameters align with experimental RSM-derived data, validating a predictive mechanical model for critical thickness and providing a foundational reference for device structure design.

Keywords: Strain relaxation, corundum α-(AlxGa1-x)2O3, epitaxy growth, MOCVD, DFT simulation