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

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 degrees 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 degrees 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.