Abstract
The thermal stability of α-Ga2O3 films grown on c-plane sapphire substrates was investigated. A strong correlation was found between thermal stability and film thickness: the more the α-Ga2O3 films maintained the α-phase upon heating at higher annealing temperature, the thinner they were. Transmission electron microscopy observations revealed that the phase transition of the α-Ga2O3 film to the thermodynamically most stable β-phase had the orientation relationship of β-Ga2O3 2̄01 || sapphire [0001]. High-temperature x-ray diffraction measurement for the α-Ga2O3 film showed the relationship of β-Ga2O3 4̄01/[301] || sapphire [0001] as well. The dependence of the stability boundary on the film thickness originates from a thermal stress caused by a larger thermal expansion coefficient of α-Ga2O3 than that of sapphire. Relaxation of residual stress by introducing a selective area growth technique enhanced the thermal stability of α-Ga2O3 so that α-Ga2O3 maintained the corundum structure upon heating at 800 °C, although a small diffraction peak from β-Ga2O3 was detected by x-ray diffraction measurement. The enhanced thermal stability of α-Ga2O3 widens device process windows as well as growth windows.
Highlights
Α-Ga2O3 films were grown on c-plane sapphire substrates using mist-chemical vapor deposition (CVD).[2,20–22] Gallium(III) trichloride (GaCl3) or gallium(III) acetylacetonate [Ga(acac)3] was dissolved in a mixed solution of H2O and HCl
C-plane sapphire substrates are generally used for the growth of α-Ga2O3 via mist-CVD and halide vapor phase epitaxy (HVPE);[19,21–23,33,34] in this study, we report the enhancement of thermal stability of α-Ga2O3 films grown on c-plane sapphire at scitation.org/journal/adv up to 800 ○C by decreasing the film thickness and utilizing the selective area growth technique
The phase stability of the α-Ga2O3 films against the thermal treatment was investigated by symmetric x-ray diffraction (XRD) 2θ/ω measurements using a Rigaku ATX system at room temperature
Summary
Α-Ga2O3 films were grown on c-plane sapphire substrates using mist-CVD.[2,20–22] Gallium(III) trichloride (GaCl3) or gallium(III) acetylacetonate [Ga(acac)3] was dissolved in a mixed solution of H2O and HCl. C-plane sapphire substrates are generally used for the growth of α-Ga2O3 via mist-CVD and HVPE;[19,21–23,33,34] in this study, we report the enhancement of thermal stability of α-Ga2O3 films grown on c-plane sapphire at scitation.org/journal/adv up to 800 ○C by decreasing the film thickness and utilizing the selective area growth technique.
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