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 K͒ 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 InSe and with the same pressure dependence. The reversible increase of its linewidth above 1 GPa is associated to a direct-to-indirect band-gap crossover between valence band maxima. The reversible decrease of its intensity above 4 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 InSe provided by these measurements agrees with the previous analysis of the optical absorption coefficient of InSe and In 1−x Ga x Se.

High pressure and high magnetic field behaviour of free and donor‐bound‐exciton photoluminescence in InSe

“…We also observed, above 2 GPa, a decrease of the PL intensity similar to the one reported by Manjon et al [2]. This decrease was explained as a signature of a direct-toindirect band crossover in the valence band predicted by band structure calculations [1].…”

“…This decrease was explained as a signature of a direct-toindirect band crossover in the valence band predicted by band structure calculations [1]. Furthermore, beyond 4 GPa the PL intensity is quickly quenched as also observed by the same authors [2], who assigned this PL quenching to a direct-to-indirect conduction band crossover from Z to B edge of the Brillouin zone.…”

“…First, the electron effective mass is expected to increase at a slower rate than the band gap, as it is basically determined by higher energy direct allowed transitions with lower pressure coefficient [12,13]. Second, the sharp decrease of the slope starting at 3 GPa could be viewed as a signature of direct-indirect conduction band crossover that have been evidenced by intrinsic photoluminescence at room temperature, as electrons in the conduction band minimum at the Brillouin zone edge are expected to have a much higher effective mass [2].…”

“…1 Introduction Although optical and electronic properties of III-VI layered semiconductor family have been investigated since decades, the detailed band structure of γ-polytype InSe was established only recently, based on powerful numerical methods [1] and later photoluminescence measurements under high pressure [2]. InSe exhibits unusual optical properties like high gain in stimulated emission at room and low temperatures [3], in addition to high anisotropy and non linear effects [5,6].…”

Electronic and optical properties of two-dimensional InSe from a DFT-parametrized tight-binding model

“…While in its bulk form InSe [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] is a direct gap semiconductor 37 , its electronic structure undergoes significant changes upon exfoliation to few-layer or monolayer thickness, with particularly interesting optical properties observed in recent experiments 1,38 . Density functional theory (DFT) calculations for single layer crystals of InSe 39,40 predict a large increase in the band gap as compared to bulk crystals, with the valence band maximum slightly shifted from the Γ point.…”