Superlinear increase of photoluminescence with excitation intensity in Zn-doped GaN

We have observed a superlinear increase of photoluminescence (PL) intensity in a narrow range of excitation intensities for Zn-doped GaN. The characteristic intensity at which the abrupt increase occurs increases with increasing temperature. This is unlike the usual observations for defects in semiconductors in which the PL intensity increases linearly with excitation intensity, saturating at high intensity because defects become saturated with photogenerated charge carriers. The observed phenomenon is attributed to a redirection of electron and hole flow from nonradiative centers at low excitation intensity to a recombination path via the Zn sub(Ga) acceptor at high excitation intensity. This is the same explanation responsible for the abrupt thermal quenching of PL reported earlier [Reshchikov et al., Phys. Rev. B 84, 075212 (2011) (http://dx.doi.org/10.1103/PhysRevB.84.075212).]