Pressure and temperature effects on optical transitions in cubic GaN

Pressure and temperature effects on optical transitions in cubic GaN grown on a GaAs substrate have been studied by photoluminescence (PL) spectroscop y at hydrostatic pressures up to 9 GPa (10 K) and as a function of temperat ure (10-300 K) at ambient pressure. The dominant emissions at 10 K and ambi ent pressure are assigned to the bound-exciton transition (zero-phonon line ), the donor-acceptor-pair (DAP) emission, and, tentatively, to the first t hree LO-phonon replicas of the bound exciton. These PL features shift to hi gher energy with increasing pressure. The pressure coefficients indicate th at the observed recombination processes involve states which are closely re lated to the band edges. Temperature-induced evolutions from bound to free- exciton (FE) transition and DAP emission to free-to-bound transition are re solved. The binding energies of the FE and donor and acceptor levels in cub ic GaN have been determined from the temperature and power-density dependen ce of the PL emission energies. (C) 1999 American Institute of Physics. [S0 021-8979(99)08014-7].