RF-MBE growth of nitride semiconductors on ScAlMgO₄ substrates

Abstract

  ScAlMgO₄ (SAM) has attracted attention as a substrate for fabricating bulk GaN crystals and InGaN template substrates. Radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE) is preferred for the growth of the first (In)GaN template layers to avoid the contamination of the epilayers by the constituent element atoms of the SAM substrate. We have grown GaN and InGaN films directly on SAM substrates without any buffer layers using RF-MBE. The (In)GaN/SAM interface was atomically abrupt and no significant contamination in the epilayer was observed. Nearly lattice-matched InGaN was obtained by the optimal growth temperature and source fluxes. However, the extraordinarily large step height close to three bilayers of wurtzite (WZ-) GaN and low temperature growth in MBE results in the mixing of the metastable zincblende (ZB) phase in the GaN films. High-temperature growth on a SAM substrate with wider terraces and increasing the film thickness suppressed the ZB mixing and a pure WZ-GaN layer was obtained.