ODEPR and yellow luminescence intensity in GaN under high pressure

Abstract

Optically detected electron paramagnetic resonance (ODEPR) measurements in the yellow luminescence (YL) under pressures up to 7 GPa have been performed. A non-magnetic diamond anvil cell was designed, into which microwaves in the 4 mm band (72 GHz) could be coupled. One of the main limiting factors for the ODEPR measurements in the YL at high pressures is the strongly decreased the YL intensity at low temperatures. At normal pressure, when cooling the sample, the YL intensity increases. Under pressures of 5–10.8 GPa, the YL intensity decreases significantly upon cooling. ODEPR spectra of the undoped MOVPE GaN layer on sapphire measured in YL at 1.5 K at normal pressure showed resonance lines at g ||=1.989, and g ||=1.952 and a shoulder with g ||=1.958, respectively. At low temperatures under pressures of 5–10.8 GPa, a part of the YL intensity remains, but only the ODEPR line at g ||=1.989 is measured while that at g ||=1.952 disappears. The disappearing part of the YL is due to a donor–acceptor recombination from a DX-like donor, which is attributed to the oxygen on nitrogen sites (O N) in agreement with theory and other experiments.