# Out-of-plane orientation of luminescent excitons in atomically thin indium selenide flakes

## TL;DR

This paper demonstrates that layered InSe flakes host luminescent excitons with out-of-plane dipole orientation, contrasting with in-plane dipoles in other TMDs, highlighting InSe's potential for advanced optoelectronic applications.

## Contribution

The study provides experimental and theoretical evidence that InSe has intrinsic out-of-plane luminescent excitons, a property not previously established for this material.

## Key findings

- InSe exhibits out-of-plane luminescent excitons.
- WSe2 and MoSe2 have in-plane dipoles at room temperature.
- InSe's optical properties are highly tunable and promising for photonic devices.

## Abstract

Van der Waals materials offer a wide range of atomic layers with unique properties that can be easily combined to engineer novel electronic and photonic devices. A missing ingredient of the van der Waals platform is a two-dimensional crystal with naturally occurring out-of-plane luminescent dipole orientation. Here we measure the far-field photoluminescence intensity distribution of bulk InSe and two-dimensional InSe, WSe$_2$ and MoSe$_2$. We demonstrate, with the support of ab-initio calculations, that layered InSe flakes sustain luminescent excitons with an intrinsic out-of-plane orientation, in contrast with the in-plane orientation of dipoles we find in two-dimensional WSe$_2$ and MoSe$_2$ at room-temperature. These results, combined with the high tunability of the optical response and outstanding transport properties, position layered InSe as a promising semiconductor for novel optoelectronic devices, in particular for hybrid integrated photonic chips which exploit the out-of-plane dipole orientation.