Dramatic thermal quenching of photoluminescence in Zn‐doped GaN

Abstract

AbstractWe report on the dramatic thermal quenching of the blue luminescence (BL) band in high‐resistivity Zn‐doped GaN. In conductive n ‐type GaN samples, the thermal quenching of this band begins at T0 = 200 K, and the activation energy of this thermal quenching is about 0.35 eV, which agrees with the ionization energy of the ZnGa acceptor. However, in high‐resistivity Zn‐doped GaN, the BL intensity drops by several orders of magnitude at a characteristic temperature T *. Interestingly, T * increases with increasing excitation intensity; i.e., the quenching is tunable. When the temperature of the sample is fixed, the dependence of PL intensity on the excitation intensity exhibits an abrupt, stepwise increase at a certain excitation intensity, and the value of the latter depends on temperature. All of the observed effects can be explained in a model involving three types of defects: a shallow donor, the ZnGa acceptor, and a deep donor. The latter is responsible for the nonradiative recombination. The abrupt and tunable thermal quenching of the Zn‐related BL band in high‐resistivity GaN samples is caused by a sudden transition of the system from the inverse population of levels at T < T * (where low‐resistivity n ‐type conductivity under illumination is predicted) to the quasi‐equilibrium population at T > T * (a p ‐type, or high‐resistivity n ‐type conductivity). This transition is initiated by the thermal emission of holes from the ZnGa acceptor to the valence band and their subsequent recombination with electrons via deep nonradiative defects. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)