Ultraviolet anti-Stokes photoluminescence in GaN single crystals

Abstract

Ultraviolet anti-Stokes photoluminescence (ASPL) is observed under continuous visible light excitation in a GaN single crystal at 4 and 77 K. The ASPL spectra are almost the same 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 intensity dependence of the ASPL intensity, we propose a two-step two-photon absorption mechanism through an electron trapped at a deep ionized donor with a lifetime of 1.45 ms.

Properties of ultraviolet anti‐Stokes photoluminescence in ZnO single crystals

“…We have now identified similar phenomenon in a ZnO crystal. In this paper, the ASPL in ZnO single crystal is reported and is interpreted in terms of the mechanism referred with that proposed in the previous paper 5.…”

“…Several ASPL in semiconductors have been studied for several decades 1, 2. ASPL has been observed in wide band gap semiconductors, such as GaN quantum well structure by Hellmann et al, in bulk GaN by Toda et al and our group, and in free standing GaN by Tripathy et al 3–6. It has also been observed in ZnO microcrystals by Cao et al 7.…”

“…The PL was focused on the entrance slit of a monochromator with a reciprocal dispersion of 22 nm/mm and detected using an integrated charge‐coupled device camera (Princeton Instruments 576G) with a gate width of 4.7 µs. The experimental techniques are described in detail elsewhere 5.…”

“…The ASPL spectrum for the GaN band edge region under weak excitation using a visible continuous‐wave (cw) laser is the same as the PL spectrum under direct excitation by a ultraviolet (UV) light source except for the re‐absorption effect of the ASPL 5. We previously proposed a two‐step two‐photon absorption process with a deep donor intermediate state with a long lifetime of 1.45 ms for interpreting appearance of the ASPL.…”

Phonon-assisted ultraviolet anti-Stokes photoluminescence from GaN film grown on Si (111) substrate

“…The mechanisms for ASPL can be attributed to multiphoton absorption including two-photon absorption, [1][2][3][4][5] Auger fountain process, 6 and the absorption of phonons. The ASPL peaks are observable only at sufficiently low temperatures.…”