器件不对称性和肖特基势垒对二维光电晶体管螺旋度依赖光响应的作用
The role of device asymmetries and Schottky barriers on the helicity-dependent photoresponse of 2D phototransistors
摘要：
圆形光电流（CPC），即圆形光电流（CPGE）和光子拖曳效应，最近被报道在单层和多层过渡金属二硫族化物（TMD）光电晶体管。然而，这些效应出现的基本物理学尚未完全理解。特别地，CPGE的出现与二维TMD的D3 h晶体对称性不相容，并且只有当电子态的对称性受到诸如外部电场或机械应变的影响而降低时才是可能的。在基于TMD的晶体管中几乎普遍存在的肖特基接触可以提供高电场，从而导致器件中的对称性破坏。在这里，我们调查这些肖特基接触CPC的影响，通过表征的螺旋度依赖的单层MoSe 2器件的光响应与直接金属MoSe 2肖特基接触和h-BN隧道势垒的接触。我们发现，当器件中存在肖特基势垒时，CPC的额外贡献变得允许，从而导致CPC在法向入射时出现照明。
英文摘要：
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.
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