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 D_3h 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.

圆形光电流（CPC），即圆形光电流（CPGE）和光子拖曳效应，最近已在单层和多层过渡金属二卤化二硫（TMD）光电晶体管中得到报道。但是，尚未完全了解这些效应出现的基本物理原理。特别是CPGE的出现与D _3h不兼容二维TMD的晶体对称性，并且只有在由于外部电场或机械应变等影响而降低了电子态对称性的情况下，才有可能实现。肖特基触点几乎在基于TMD的晶体管中无处不在，可以提供高电场，从而导致器件对称性破坏。在这里，我们通过表征具有直接金属-MoSe ₂肖特基接触以及在接触处具有h-BN隧道势垒的单层MoSe ₂器件的依赖于螺旋度的光响应来研究这些肖特基接触对CPC的影响。我们发现，当器件中存在肖特基势垒时，允许对CPC的其他贡献，从而导致在垂直入射时出现用于照明的CPC。