Photoluminescence and charge transfer in the prototypical 2D/3D semiconductor heterostructure MoS$_2$/GaAs

TL;DR

This study investigates how different GaAs substrates affect the photoluminescence and charge transfer in MoS₂/GaAs heterostructures, revealing significant emission reduction and charge exchange mechanisms crucial for device optimization.

Contribution

It provides new insights into the effects of substrate doping on MoS₂ photoluminescence and charge transfer, highlighting the importance of band alignment in 2D/3D heterojunctions.

Findings

MoS₂ photoluminescence decreases by an order of magnitude on GaAs substrates.

The trion to A-exciton emission ratio depends on substrate doping type.

Kelvin probe measurements suggest type-I band alignment facilitating exciton transfer.

Abstract

The new generation of two-dimensional (2D) materials has shown a broad range of applications for optical and electronic devices. Understanding the properties of these materials when integrated with the more traditional three-dimensional (3D) semiconductors is an important challenge for the implementation of ultra-thin electronic devices. Recent observations have shown that by combining MoS$_2$ with GaAs it is possible to develop high quality photodetectors and solar cells. Here, we present a study of the effects of intrinsic GaAs, p-doped GaAs, and n-doped GaAs substrates on the photoluminescence of monolayer MoS$_2$. We observe a decrease of an order of magnitude in the emission intensity of MoS$_2$ in all MoS$_2$/GaAs heterojunctions, when compared to a control sample consisting of a MoS$_2$ monolayer isolated from GaAs by a few layers of hexagonal boron nitride. We also see a dependence of the trion to A-exciton emission ratio in the photoluminescence spectra on the type of substrate, a dependence that we relate to the static charge exchange between MoS$_2$ and the substrates when the junction is formed. Scanning Kelvin probe microscopy measurements of the heterojunctions suggest type-I band alignments, so that excitons generated on the MoS$_2$ monolayer will be transferred to the GaAs substrate. Our results shed light on the charge exchange leading to band offsets in 2D/3D heterojunctions which play a central role in the understanding and further improvement of electronic devices.