Band structure of indium selenide investigated by intrinsic photoluminescence under high pressure

Abstract

This paper reports on photoluminescence experiments in $n$-type indium selenide $(T=300\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ under hydrostatic pressure up to 7 GPa at low and high excitation densities. Photoluminescence measurements at low excitation density exhibit a broad band around the energy of the direct band gap of $\mathrm{InSe}$ and with the same pressure dependence. The reversible increase of its linewidth above $1\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ is associated to a direct-to-indirect band-gap crossover between valence band maxima. The reversible decrease of its intensity above $4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ is interpreted as evidence of a direct-to-indirect band-gap crossover between conduction band minima. Photoluminescence measurements under high excitation density exhibit several spontaneous and stimulated emission bands. The different components of these bands can be attributed to radiative emission from different minima of the conduction band to different maxima of the valence band in the framework of the band-gap renormalization theory in a multivalley scenario. The image of the electronic band structure of $\mathrm{InSe}$ provided by these measurements agrees with the previous analysis of the optical absorption coefficient of $\mathrm{InSe}$ and ${\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}\mathrm{Se}$.