Anti-Stokes photoluminescence from n-type free-standing GaN at room temperature based on competition between phonon-assisted and two-photon absorption

摘要

We have observed anti-Stokes photoluminescence from n-type free-standing GaN at room temperature. Such a process is caused 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 the donor-acceptor pair transition plays an important role in anti-Stokes photoluminescence. Our study could result in efficient laser cooling of semiconductors.