Single crystalline boron rich B(Al)N alloys grown by MOVPE

Abstract

Boron rich BAlN alloys have been grown on 2-inch sapphire substrates by Metal-Organic Vapor Phase Epitaxy. The surface morphology of BAlN alloys exhibits a transition stage from a completely two-dimensional to a three-dimensional granular surface with an increased trimethylaluminum/group III (TMAl/III) ratio. Only a shift in the position of the 002 plane reflection peak to higher diffraction angles in the 2θ−ω scan along with a decrease in intensity was observed, specifying formation of layered BAlN alloys up to a TMAl/III ratio of 14. AlN phase separation was observed while increasing the TMAl/III ratio to 25, supporting SEM observations. Secondary-ion mass spectrometry measurements confirmed the presence of up to 17% Al in layered BAlN alloy systems. A cross sectional transmission electron microscopy (TEM) study confirmed the layered nature of single phase BAlN alloys. It also revealed the presence of wurtzite Al rich BAlN phases in a matrix of layered hexagonal B rich BAlN. Band to band transition around 5.86 eV has been observed, which shifted slightly to lower energy with increasing Al incorporation. The bowing parameter (C) in boron rich BAlN alloy systems was evaluated to be around 0.65 ± 0.05 eV. Encouraging results were obtained on boron rich BAlN alloy formation, motivating further exploration of growth conditions and study of BAlN fundamental properties for applications in deep UV optoelectronics.