Anti-Stokes photoluminescence in GaN single crystals and heterostructures

Abstract

We review some of our recent results following the investigation of anti-Stokes photoluminescence (PL). Indeed, we have observed anti-Stokes photoluminescence from n-type free-standing GaN at room temperature. Such a process is induced by phonon-assisted absorption. When the excitation photon energy is sufficiently below the donor-acceptor transition energy, however, two-photon absorption becomes the dominant mechanism for anti-Stokes photoluminescence. By measuring the dependences of the photoluminescence spectra on temperature, excitation power, and excitation photon energy, we have demonstrated that donor-acceptor pair transition plays an important role in the generation of anti-Stokes photoluminescence. Our study could result in efficient laser cooling of semiconductors.