Ultraviolet anti-Stokes photoluminescence inInxGa1−xN/GaNquantum-well structures

Abstract

Ultraviolet anti-Stokes photoluminescence (PL) is observed in ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}/\mathrm{GaN}$ multiple quantum wells. The observed anti-Stokes PL exhibits a quadratic dependence on the excitation energy density. Anti-Stokes PL excitation spectrum is proportional to the optical absorption spectrum of the ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ quantum wells. Time-resolved PL measurement shows that a decay of the anti-Stokes PL is slower than that of the GaN PL under the excitation above the band gap of the GaN barrier, and it is half the time constant of the ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ PL decay. A two-step two-photon absorption process is directly observed by means of two-color pump-and-probe experiment. It is considered that the anti-Stokes PL is caused by a two-step two-photon absorption process involving a localized state in the ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ quantum wells as the intermediate state, and that the second absorption step is provided by photon recycling of the ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ PL.