Macro-scale phase purity and epitaxiality of pulse-laser-deposited Ga2O3 on c-plane sapphire

Abstract

In this work, the phase-purity and epitaxial quality of Ga₂O₃ thin films, grown by pulsed laser deposition, on c-plane sapphire substrates, is systematically investigated, primarily by a combination of different high-resolution X-ray-diffraction-based analyses. We observe that while the oxide grows predominantly in the ($\overline{2}01$) orientation of the monoclinic $\beta$-phase, it contains some volume fraction of the hexagonal α-phase, tentatively close to the film-substrate interface. This is in contrast to some earlier observations, where the monoclinic $\beta$-phase was found to stabilize atop exactly three monolayers of the α-phase. However, no other polymorphic phases could be identified in the oxide films, irrespective of the film thickness. Phase-purity and epitaxial quality of $\beta$-Ga₂O₃ thin films, on macroscopic length-scales probed by X-ray diffraction techniques, are critical attributes determining the applicability of this ultra-wide-band-gap semiconductor for development of high-performance optoelectronic and microelectronic devices.