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

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.

Twisted black phosphorus–based van der Waals stacks for fiber-integrated polarimeters

“…Because of the broken inversion symmetry of a material, the illumination of CP light onto the material results in a helicity-dependent photocurrent, which is called CPGE (34)(35)(36)(37)(38)(39)(40)(41). In our polarimeter, the presence of anisotropic electric fields near the metal-BP contacts (originating from the Schottky barriers) will reduce the symmetry of the unit and result in a net CP photocurrent (42)(43)(44). In Fig.…”

Ultrafast Drift Current Terahertz Emission Amplification in the Monolayer WSe2/Si Heterostructure

“…Therefore, it is crucial to characterize the valley-coupled photocurrent at room temperature. Recently, it has been reported that the surface symmetry breaking and charge transfer in the TMD-based heterostructure could help to enhance the photoelectric response in TMDs, , which is expected to provide a feasible way to detect the valley photocurrent in TMDs at room temperature.…”