Thermal stability of epitaxial α-Ga2O3 and (Al,Ga)2O3 layers on m-plane sapphire

Abstract

Here, we have explored the thermal stability of α-(Al,Ga)2O3 grown by the molecular-beam epitaxy on m-plane sapphire under high-temperature annealing conditions for various Al compositions (i.e., 0%, 46%, and 100%). Though uncapped α-Ga2O3 undergoes a structural phase transition to the thermodynamically stable β-phase at high temperatures, we find that an aluminum oxide cap grown by atomic layer deposition preserves the α-phase. Unlike uncapped α-Ga2O3, uncapped α-(Al,Ga)2O3 at 46% and 100% Al content remain stable at high temperatures. We quantify the evolution of the structural properties of α-Ga2O3, α-(Al,Ga)2O3, and α-Al2O3 and the energy bandgap of α-Ga2O3 up to 900 °C. Throughout the anneals, the α-Ga2O3 capped with aluminum oxide retains its high crystal quality, with no substantial roughening.

Electrical and Recombination Properties of Polar Orthorhombic κ-Ga2O3 Films Prepared by Halide Vapor Phase Epitaxy

“…These problems are less severe when growth is carried out on sapphire planes other than the basal plane. The thermal stability that exists in MBE growth has been shown to greatly increase (up to about 900 °C) when masking the surface with α-(Al x Ga 1−x ) 2 O 3 capping layers [ 20 ]. The defect studies in α-Ga 2 O 3 are not as advanced as in β-Ga 2 O 3 , but some work on the theory of defects has been started [ 21 ].…”

Pseudomorphic growth of Si-doped α-(AlGa)2O3 on m-plane α-Al2O3 substrates by molecular beam epitaxy

“…21) The thermal stability of α-(AlGa) 2 O 3 increases as the Al composition is increased. 22) Although α-(Al 0.6 Ga 0.4 ) 2 O 3 remains stable even at 1100 °C, 23) alloy instability occurs during high-temperature growth. 24) The ability to control the temperature of the thermal treatments is thus significantly important for α-(AlGa) 2 O 3 .…”

Growth of α-(AlGa)2O3 alloy thin films on c-sapphire substrates by mist chemical vapor deposition using acetylacetonated Al and Ga solutions

“…12) This can be obtained as a thin film by epitaxial growth on a sapphire substrate, 13) and it can be alloyed with corundum-structured alpha indium oxide (α-In 2 O 3 ) and alpha aluminum oxide (α-Al 2 O 3 ). 14) At present, α-Ga 2 O 3 can be prepared using mist chemical vapor deposition (mist-CVD), 13) halide vapor phase epitaxy (HVPE), 15) molecular beam epitaxy, 16) metalorganic chemical vapor deposition, 17) and atomic layer deposition. 18,19) Among these methods, mist-CVD and HVPE are currently those capable of growing a homogeneous thick α-Ga 2 O 3 layer on sapphire.…”