Ultraviolet anti-Stokes photoluminescence in GaN single crystals

Abstract

Ultraviolet anti-Stokes photoluminescence (ASPL) is observed under continuous visiblelight excitation in a GaN single crystal at 4 and 77 K. The ASPL spectra are almost thesame as the Stokes photoluminescence (SPL) spectra under band-to-band excitation.Namely, we observe ASPL due to bound and free excitons at 4 and 77 K, respectively.Based on the temporal decay, the excitation spectrum and the excitation intensitydependence of the ASPL intensity, we propose a two-step two-photon absorptionmechanism through an electron trapped at a deep ionized donor with a lifetime of 1.45 ms.