Growth of semipolar (202̄1) GaN layers on patterned silicon (114) 1° off by Metal Organic Vapor Phase Epitaxy

Abstract

With the objective of introducing further GaN semipolar orientations adequate for the fabrication of optoelectronic devices on silicon, we report on the selective area growth of semipolar (202̄1) GaN layers on patterned silicon (114) 1° off substrates. The patterning and subsequent anisotropic etching of the Si substrates allows exposing Si {111}-type facets on which GaN grows along the [0001] direction. Upon coalescence of neighboring GaN stripes, a continuous (202̄1) semipolar layer is obtained, displaying a facetted surface morphology dominated by more thermodynamically-stable crystallographic planes, i.e. semipolar (101̄1) and nonpolar (101̄0). Transmission electron microscopy shows that dislocation bending in the early growth stages determines the structural quality of the final semipolar (202̄1) layer. This is confirmed by X-ray rocking curves displaying full width at half-maximum values comparable to those of (202̄1) GaN epilayers of equivalent thickness grown on patterned sapphire. Optical characterization displays regions having threading dislocations and stacking faults alternating with almost defect-free regions, which correlate well with the transmission electron microscopy study.