Characterization of MOCVD regrown p-GaN and the interface properties for vertical GaN power devices

Abstract

p-type gallium nitride (GaN) layers were regrown on etched surfaces on free-standing GaN substrates by metalorganic chemical vapor deposition with different growth rates by adjusting trimethylgallium flow rates. The roughness of the samples increases almost linearly with the growth rate, with an increase rate of 0.6 nm (μm h−1) −1. The screw dislocation density of the samples increases significantly when the growth rate is higher than 0.5 μm h − 1. When the magnesium (Mg) doping concentration is higher than 7.0 × 1019 cm−3, transmission electron microscopy images clearly show the regrowth interfaces, and Mg precipitate occur in high-doping p-GaN layers. Under the same bis(cyclopentadienyl)magnesium (Cp2Mg) flow rate, the Mg doping concentration decreases with the growth rate. The samples with different growth rates show different electroluminescence spectra. The emission peak at 2.8 eV is due to the transition from the deep donor level to the Mg acceptor level. And the intensity of this peak drops with increasing growth rate due to reduction of Mg acceptors. Transitions related to defect levels appears with increasing growth rate due to an increased screw dislocation density.