Direct Growth of Nearly Lattice‐Matched InGaN on ScAlMgO4 Substrates Using Radio‐Frequency Plasma‐Assisted Molecular Beam Epitaxy

Abstract

ScAlMgO4 (SAM) has attracted considerable attention as a substrate for growing InGaN template layers owing to its lattice matching with In0.17Ga0.83N. Furthermore, radio‐frequency plasma‐assisted molecular beam epitaxy (RF‐MBE) can be utilized to grow (In)GaN directly on SAM substrates because the growth is conducted at relatively low temperatures without reactive gases. This prevents the diffusion and desorption of the constituent elements of the SAM substrate. In this study, the substrate‐temperature dependence of the direct growth of InGaN on SAM substrates is investigated through RF‐MBE. In droplets are formed below 600 °C, whereas, the In content of the InGaN crystal decreases rapidly, and the surface roughness increases at ≈650 °C. These results are attributed to the acceleration of In desorption at higher temperatures. The improvement in crystal coherency moderates above 600 °C. Therefore, a nearly lattice‐matched In0.18Ga0.82N film is grown at an optimal temperature of 600 °C by adjusting the group‐III metal fluxes. The resulting film is continuous and relatively flat, with no droplets. The dislocation density with screw component is one order of magnitude lower than that of the lattice‐mismatched InGaN. The dislocation density of the InGaN film is comparable to that of a film grown by metal‐organic vapor‐phase epitaxy.