Predictions for Yellow Luminescence In Cubic GaN Under Hydrostatic Pressure*

Cubic GaN has current interest as a green light source(Bayram,2017), and as a bright, single photon emitter (Aharonovich, 2016). We report defect studies in cubic GaN using the local moment counter charge technique (LMCC) as a function of pressure, enabling experimental predictions for the behavior of the yellow luminescence. The LMCC bandgap is determined as the total defect level spectrum for all calculated, localized defect levels. Studying defects as a function of cell size (64 to 1000 atoms) using the standard PBE functional, we obtained a predicted band gap of 3.47 eV, compared to a Kohn-Sham band gap of 2.4 eV. Under 12 GPa hydrostatic pressure, using the same technique, we predict the bandgap grows by 0.42 eV. Several candidates have been identified as origins of yellow luminescence in wurtzite GaN, including, among others, the C_N (o/+) and -/o transitions (Lyons, 2014), and the V_Ga (+3/+2) transition (Lyons, 2017). For C_N we predict peaks, at 2.25 eV (2.48 eV) and 2.71 eV (3.02 eV), while for V_Ga, we predict a luminescence peak at 2.23 eV (2.711 eV) at 0GPa (12 GPa). In both cases, the shift is primarily from changes in the zero phonon line, with changes in the Frank-Condon shift of ~ 10-20 meV.