Effects of low-temperature annealing on net doping profile of Mg-ion-implanted GaN studied by MOS capacitance–voltage measurement

Abstract

Effects of long-term low-temperature cap annealing on the net doping profile of Mg-ion-implanted GaN were studied using MOS structures before activation annealing. Mg ions were lightly implanted into n-type GaN to maintain the n-type conduction. Various cap-layer materials, i.e. Al2O3, SiN, SiO2 and capless, for low-temperature annealing were examined. Doping profiles were derived from capacitance–voltage (C–V) curves. Before 600 °C annealing, negatively charged defects were distributed on the shallower side of the detection depth range, whereas positively charged defects existed on the deeper side. Upon 600 °C annealing, however, the doping profile changed toward a flat shape regardless of the cap-layer material used during annealing. The observed profile change was likely caused by the diffusion of defects. Detailed analyses of C–V characteristics showed that the highly likely cause of the observed phenomena is the diffusion of Ga and N interstitials.