Ternary AlGaN Alloys with High Al Content and Enhanced Compositional Homogeneity Grown by Plasma-Assisted Molecular Beam Epitaxy

Abstract

We have studied the influence of III/N flux ratio and growth temperature on structural and optical properties of high Al-content, around 50–60%, AlGaN alloy layers grown by plasma-assisted molecular beam epitaxy. In a first part, based on structural analysis by Rutherford Backscattering Spectroscopy, we establish that a III/N flux ratio slightly above 1 produces layers with low amount of structural defects. In a second part, we study the effect of growth temperature on structural and optical properties of layers grown with previously determined optimal III/N flux ratio. We find that optimal growth temperatures for Al 0.50 Ga 0.50 N layers with compositional homogeneity related with narrow UV photoluminescence properties are in the low temperature range for growing GaN layers, i.e., 650–680 °C. We propose that lowering Ga adatom diffusion on the surface favors random incorporation of both Ga and Al adatoms on wurtzite crystallographic sites leading to the formation of an homogeneous alloy.