Determination of the direct bandgap value in In₄Se₃ thin films

Abstract

The value and the nature of the bandgap of In4Se3 are still not well defined, with a large spread of the experimental data between 0.42 eV and 1.68 eV and an uncertain nature, predicted to be indirect by ab initio band structure calculations. Here we report on the optical transmission and photoluminescence performed in In4Se3 thin films grown by coevaporation on (0001)-oriented sapphire wafers. The quality of the polycristalline layers allows the first detection of the excitonic-like transition in the optical absorption of this compound at low temperature. The photoluminescence detected under weak laser excitation shows a bound exciton emission at 0.75 eV. Strong laser irradiation reveals a quadratic dependence of the photoluminescence intensity on the optical excitation, which demonstrates a stimulated emission at 0.79 eV in relation with an exciton-exciton scattering process. On the basis of a reasonable estimate of the exciton energy, equal to 10-15 meV, we evaluate the direct bandgap of In4Se3 to 0.82±0.01 eV at low temperature.

Effects of stresses on the thermoelectric properties of In4Se3

“…45 Additionally, we investigate the impact of the Heyd–Scuseria–Ernzerhof (HSE06) generalization on the band gap. The computed results indicate that the bandgap at 0 GPa is a direct bandgap of 1.00 eV, closely aligning with the experimental value of 0.82 eV (direct) reported by L. de Brucker et al 44…”

“…Our calculations yielded an indirect band gap of 0.15 eV in the PBE potential for In 4 Se 3 at 0 GPa, a value notably lower than the experimental value of 0.82 eV. 44 This discrepancy arises because band gap calculations using the generalized gradient approximation (GGA) typically yield values lower than the experimentally observed band gap. 45 Additionally, we investigate the impact of the Heyd-Scuseria-Ernzerhof (HSE06) generalization on the band gap.…”