Pressure and time-resolved photoluminescence studies of Mg-doped and undoped GaN

Pressure and time-resolved photoluminescence (PL) experiments were performed on undoped and Mg doped GaN homoepitaxial layers. The pressure coefficients of the following PL lines were determined: (i) exciton bound to a neutral donor (3.472 eV), (ii) exciton bound to a neutral acceptor (3.463 eV), (iii) line centered at about 3.27 eV and its two LO (92 meV) phonon replicas. In the time-resolved measurements, we observed that the latter PL line corresponds to a slow process (delay time is in the millisecond range). This observation strongly supports the conclusion that donor-acceptor pairs are responsible for this radiative transition. Identification of the radiative centers and. a new explanation of the radiative mechanisms (including optically active E(2)(1) phonons) are proposed.