Investigation of Mg δ-doping for low resistance N-polar p-GaN films grown at reduced temperatures by MOCVD

In this study we explored p-type delta-doping for the deposition of N-polar p-GaN films at 900 degrees C, for application in device structures containing high In composition active layers. Various delta-doping process parameters were investigated, including the duration and molar flow of the Mg precursor during each pulse as well as the delta-doping period. The results were compared to those obtained for layers grown using continuous doping. As the delta-doping period was reduced from 25 to 5 nm, the p-GaN bulk resistivity decreased from 6.8 to 2.8 Omega cm. The p-layer resistivity rose with increasing [Mg] independent of the doping scheme. For similar average [Mg], however, continuous doping resulted in a lower resistivity compared to delta-doping. This effect was more pronounced at higher [Mg], indicating that high local concentrations of Mg resulted in degradation of the electrical performance. After optimization of the p-layer structure and contact fabrication process, a minimum contact resistance of 2.77 m Omega cm(2) and a minimum resistivity of 1.33 W cm were achieved.