First-Principles Calculations of Quantum Efficiency for Point Defects in Semiconductors: The Example of Yellow Luminance by GaN: CN+ON and GaN:CN

Point defects play an important role in the photoelectrical properties of semiconductor materials, and they can be luminescence centers. However, the relationships among the observed luminescence wavelengths, intensities, and the microscopic processes are in most cases unknown, or depend heavily on parameter fitting. In this work, the light-emitting quantum efficiencies for point defects using ab initio density functional theory are calculated. The study of radiation recombination for electrons and nonradiation recombination for holes is reported here. The results show that the defect C-N transition between - and 0 charged levels and the defect C-N+O-N transition between 0 and + charged levels both may be responsible for the yellow luminescence (YL) which is observed in experiment. Moreover, the calculation shows significant thermal quenching of the YL starting at 480 K due to re-excitation of hole into the valence band from the point defects, which is in relatively good agreement with the experimentally observed value. This work shows that it is possible to use ab initio calculations to understand the microscopic mechanisms and the competitions among different channels for the light emissions caused by defects.