Yellow luminescence and carrier distribution due to polarity-dependent incorporation of carbon impurities in bulk GaN by Na flux

Abstract

We have grown a high growth rate, and low dislocation density (DD) Ga-polar GaN (DD: 4 × 105/cm2) and N-polar GaN (DD: 8 × 105/cm2) bulk single crystal using Na Flux. Variable temperature PL shows that the yellow luminescence (YL) peak energy of Ga-polar GaN (Ga-GaN) and N-polar GaN (N-GaN) are 2.31–2.30 eV and 2.28–2.26 eV, respectively. It can be found that N-GaN has a more vigorous YL intensity and a lower peak energy of YL than Ga-GaN. The variable-temperature and variable-power PL results suggest that the YL origin may be a donor-acceptor pair defect. Dislocations and defects associated with gallium vacancies that could cause YL behavior were ruled out by dislocation density determination and Raman spectroscopy, respectively. The different concentrations of carbon and oxygen in the Ga-GaN and N-GaN that were associated with the adsorption energy were discussed and proved by SIMS. The Raman results show that the carrier concentrations of Ga-polar and N-polar GaN are comparable, which may be because the higher content of carbon impurities in N-polar GaN can act as a deep acceptor to compensate for its higher content of shallow donor impurity oxygen. Therefore, it is suggested that carbon-related energy level transitions are the primary source of YL in both Ga-polar and N-polar GaN, and the compensating effect of carbon impurities leads to similar carrier concentrations in both polar planes.