Atomic scale investigation of aluminum incorporation, defects, and phase stability in β-(AlxGa1-x)2O3 films

The development of novel ultra-wide bandgap (UWBG) materials requires precise understanding of the atomic level structural origins that give rise to their important properties. We study the aluminum atom incorporation, defect formation, and their relationships with phase stability in beta-(AlxGa1-x)(2)O-3 films, a promising candidate for UWBG applications, to explain atomic scale structural characteristics and properties using a combination of quantitative scanning transmission electron microscopy (STEM) and density functional theory (DFT). Our STEM analysis indicates that similar to 54% of the incorporated Al substitutes on the octahedrally coordinated Ga-2 site in a series of films grown with different techniques and alloy concentrations. DFT calculations show that, while Al energetically prefers the octahedral site, surface reconstructions and kinetic limitations during the epitaxial growth are responsible for Al occupying both octahedral and tetrahedral sites in (AlxGa1-x)(2)O-3, ultimately limiting the stability of the beta-phase at x < similar to 50%. Local heterogeneity of composition results in the formation of a planar defect, affecting the stability of the beta-phase. The similarity of such inclusions to the metastable gamma-phase is discussed.

Automated summary

The study focuses on the aluminum atom incorporation, defect formation, and phase stability in beta-(AlxGa1-x)(2)O-3 films for ultra-wide bandgap applications, utilizing a combination of STEM and DFT to explain atomic scale structural characteristics and properties. The research finds that aluminum occupies octahedral and tetrahedral sites due to surface reconstructions and kinetic limitations, ultimately limiting the stability of the beta-phase. Local heterogeneity of composition leads to the formation of planar defects, impacting the stability of the beta-phase and resembling the metastable gamma-phase.