Improvement in the crystalline quality of GaN and defects analysis using cathodoluminescence

Abstract

The crystalline quality of GaN layer grown on 4H-SiC substrate using Metal Organic Chemical Vapor Deposition (MOCVD) has been improved by reducing the growth rate of GaN. Depth resolved CL (cathodoluminescence) study was also done to analyze the defects in the GaN layers. Two samples, one with fast growth rate (∼0.7 nm/s; Sample-A) of GaN and other with slower growth rate (∼0.2 nm/s; Sample-B) were grown. The surface morphology and crystalline quality of GaN epi-layers have been studied by Atomic Force Microscopy (AFM) and High Resolution X-Ray Diffraction (HRXRD), respectively. It was observed that growth rate of the GaN layer strongly influenced its crystalline quality and surface morphology. The GaN layer grown with slow growth rate exhibited improved surface morphology with lower rms roughness of ∼0.18 nm and lower surface pits density. X-ray rocking curve measurement for (0 0 2) and (1 0 2) planes showed that both screw and edge dislocation densities were reduced for the GaN grown with slow growth rate. Depth profiling by CL spectroscopy revealed intense Yellow (YL) and Blue luminescence (BL) band in Sample-A, while in Sample B, the YL and BL bands were much weaker. The higher yellow and blue luminescence in the GaN grown at higher growth rate may be correlated with nitrogen vacancies (VN) and two charged state of CN(−/0 and 0/+) acceptor.