HVPE growth of α- and ε-Ga2O3 on patterned sapphire substrates

Abstract

Here we report on the growth and characterisation of α- and ε-Ga2O3 epitaxial films produced by halide vapour phase epitaxy (HVPE). The films were deposited on two types of substrate: (0001) plain sapphire substrates and (0001) patterned sapphire substrates with regular cone-like features. In order to guarantee the same growth conditions on plain and patterned sapphire, the two substrates were used simultaneously in the same growth run. After the deposition the samples were studied by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical transmission (OT) spectroscopy, and cathodoluminescence (CL). The growth on plain sapphire substrate produced an 11 μm thick continuous α-Ga2O3 layer. The full width at half maximum (FWHM) of the (0006) XRD rocking curve is 180 arcsec, which indicates good crystallinity of the layer. In contrast, growth on the patterned sapphire substrate resulted in a layer with regular spaced faceted pyramids at the surface. XRD analysis revealed the presence of both α- and ε-phases in Ga2O3 grown on patterned sapphire substrate. The presence of the ε-Ga2O3 phase, which has narrower bandgap, was also confirmed by optical transmission measurements. SEM, TEM, and SEM CL observations revealed that α-Ga2O3 phase forms columnar structures on top of sapphire cone, and ε-Ga2O3 phase fills the valleys between the columns.