Understanding Optical Anisotropy in Multilayer {\gamma}-InSe and {\epsilon}-GaSe

TL;DR

This paper measures and analyzes the optical anisotropy of multilayer { extgamma}-InSe and { extepsilon}-GaSe, revealing their potential for ultrathin optoelectronic devices due to their unique anisotropic refractive indices and out-of-plane excitonic effects.

Contribution

First experimental determination of the anisotropic refractive indices of { extgamma}-InSe and { extepsilon}-GaSe, highlighting their moderate optical anisotropy and impact of out-of-plane excitons.

Findings

Both materials exhibit moderate optical anisotropy.

Out-of-plane excitons influence the c-axis refractive index.

The complex refractive indices enable accurate device simulations.

Abstract

Low-dimensional media have exhibited optical anisotropy that is unachievable in traditional 3D media due to the asymmetry of their strong, in-plane covalent bonds and weak out-of-plane van der Waals interactions. As a result, 2D media are promising building blocks for ultrathin devices such as polarimeters, polarized light sources, and active polarizers. III-VI semiconductors possess a rare property in the class of multilayered semiconductors, which is that their fundamental excitons are oriented out-of-plane. This allows them to exhibit phenomena such as transparency in the visible range while also being emissive in the visible and near-infrared ranges. Here, we report the first experimental values for the anisotropic refractive indices of {\gamma}-InSe and {\epsilon}-GaSe, and we observe the effects of the out-of-plane excitons on the c-axis refractive index. It is found that both materials exhibit moderate optical anisotropy for multilayered semiconductors. The complex, anisotropic refractive index of {\gamma}-InSe and {\epsilon}-GaSe enables the accurate simulation of these media, allowing for the design of high-performance, ultra-compact optoelectronic devices.