Effect of nucleation layer growth conditions on the defect structure in MOVPE-grown cubic GaN epitaxial layers

Abstract

A possible approach to achieve higher efficiencies and faster switching speeds in green-to-red LEDs for visible light communication is the application of GaN grown in the zincblende phase. However, zincblende GaN epilayers often exhibit an unwanted phase mixture and a rich defect structure, which can impair the performance of light emitting devices. In this study, the effect of nucleation layer growth conditions on the formation and distribution of wurtzite GaN inclusions and stacking faults in overlying zincblende GaN thin films deposited under constant conditions by metalorganic vapor-phase epitaxy have been studied. We show that the zincblende phase can be achieved with high purity using nucleation layers grown within a reasonable temperature range (560–610 °C) and at moderate V/III ratios. Nucleation layer temperatures outside this window or lower V/III ratios (<1000) favor the formation of wz GaN on the {111}A (Ga-polar) planes, whereas higher V/III ratios (>2500) at moderate temperatures lead to growth of wz GaN on the {1−11}B (N-polar) planes. Based on the experimental findings, a schematic map of the different growth regimes has been developed. We use this map to discuss how growth kinetics and thermodynamic effects influence the preferential polarity growth and defect formation in different growth regimes.