Evidence of Direct Electronic Band Gap in two-dimensional van der Waals Indium Selenide crystals

TL;DR

This study combines advanced spectroscopic techniques to demonstrate that two-dimensional InSe crystals have a direct electronic band gap of approximately 1.25 eV at the Gamma point, revealing key electronic properties relevant for optoelectronic applications.

Contribution

The paper provides the first precise experimental evidence of a direct band gap in 2D InSe using combined STS and 2PPE methods, clarifying its electronic structure.

Findings

InSe exhibits a direct band gap of about 1.25 eV at the Gamma point.

The valence band has a poorly dispersive nature with a sharp DOS near VMB.

A spin-orbit splitting of approximately 0.35 eV was observed in deeper bands.

Abstract

Metal mono-chalcogenide compounds offer a large variety of electronic properties depending on chemical composition, number of layers and stacking-order. Among them, the InSe has attracted much attention due to the promise of outstanding electronic properties, attractive quantum physics, and high photo-response. Metal mono-chalcogenide compounds offer a large variety of electronic properties depending on chemical composition, number of layers and stacking-order. Among them, the InSe has attracted much attention due to the promise of outstanding electronic properties, attractive quantum physics, and high photo-response. Precise experimental determination of the electronic structure of InSe is sorely needed for better understanding of potential properties and device applications. Here, combining scanning tunneling spectroscopy (STS) and two-photon photoemission spectroscopy (2PPE), we demonstrate that InSe exhibits a direct band gap of about 1.25 eV located at the Gamma point of the Brillouin zone (BZ). STS measurements underline the presence of a finite and almost constant density of states (DOS) near the conduction band minimum (CBM) and a very sharp one near the maximum of the valence band (VMB). This particular DOS is generated by a poorly dispersive nature of the top valence band, as shown by angle resolved photoemission spectroscopy (ARPES) investigation. technologies. In fact, a hole effective mass of about m/m0 = -0.95 gammaK direction) was measured. Moreover, using ARPES measurements a spin-orbit splitting of the deeper-lying bands of about 0.35 eV was evidenced. These findings allow a deeper understanding of the InSe electronic properties underlying the potential of III-VI semiconductors for electronic and photonic