The role of device asymmetries and Schottky barriers on the helicity-dependent photoresponse of 2D phototransistors

TL;DR

This study investigates how device asymmetries and Schottky barriers influence the helicity-dependent photoresponse in 2D TMD phototransistors, revealing that Schottky contacts enable circular photocurrents at normal incidence.

Contribution

It demonstrates that Schottky barriers induce symmetry breaking in 2D TMD devices, allowing circular photocurrents to emerge under conditions where they are typically forbidden.

Findings

Schottky contacts enable CPC at normal incidence.

Symmetry breaking by Schottky barriers affects photoresponse.

Device asymmetries influence helicity-dependent effects.

Abstract

Circular photocurrents (CPC), namely circular photogalvanic (CPGE) and photon drag effects, have recently been reported both in monolayer and multilayer transition metal dichalcogenide (TMD) phototransistors. However, the underlying physics for the emergence of these effects are not yet fully understood. In particular, the emergence of CPGE is not compatible with the D3h crystal symmetry of two-dimensional TMDs, and should only be possible if the symmetry of the electronic states is reduced by influences such as an external electric field or mechanical strain. Schottky contacts, nearly ubiquitous in TMD-based transistors, can provide the high electric fields causing a symmetry breaking in the devices. Here, we investigate the effect of these Schottky contacts on the CPC by characterizing the helicity-dependent photoresponse of monolayer MoSe2 devices both with direct metal-MoSe2 Schottky contacts and with h-BN tunnel barriers at the contacts. We find that, when Schottky barriers are present in the device, additional contributions to CPC become allowed, resulting in emergence of CPC for illumination at normal incidence.