Photoluminescence from (0Â 0Â 0Â 1) GaN grown by the acidic ammonothermal technique

We report the observation of two emissions from the (0 0 0 1) face of GaN grown by the acidic ammonothermal method, which appears rather unusual. Excitonic emission at 3.357 eV (called Y4) by photoluminescence was observed which is possibly due to an exciton bound to neutral donors related to structural defects of GaN. Deep level luminescence at 1.93 eV was also observed, which had two transition possibilities of a simple two-level transition and donor-acceptor pairs.