Epitaxial lateral overgrowth of r-plane α-Ga2O3 with stripe masks along ⟨1¯21¯0⟩

We demonstrated the epitaxial lateral overgrowth (ELO) of (1¯012) (r-plane) α-Ga2O3 using a striped mask pattern along ⟨1¯21¯0⟩. α-Ga2O3 stripes with an asymmetric cross-sectional shape were formed selectively on the windows at the initial growth stage. They grew vertically and laterally to coalesce with each other, and a compact film was obtained. The film surface exhibited wave-like morphology with macro-scale inclined terraces and steps because of the asymmetric cross-sectional stripe shape. The macrosteps moved laterally like traveling waves as the growth proceeded. Transmission electron microscopy revealed that a domain on a window grew toward the inclined c-axis direction to cover the adjacent domain after the coalescence. As a result, the dislocations, which propagated into the α-Ga2O3 stripe from the seed layer through the window, bent toward the c axis and concentrated in a narrow area. This concentration should enhance the pair annihilation. Therefore, the dislocation density was markedly reduced on the top surface including the areas above the windows and coalesced boundaries in contrast to the cases of conventional c-, a-, and m-plane ELO.