Zero-Bias Photodetection in 2D Materials via Geometric Design of Contacts

Structural or crystal asymmetry is a necessary condition for the emergence of zero-bias photocurrent in light detectors. Structural asymmetry has been typically achieved via p-n doping, which is a technologically complex process. Here, we propose an alternative approach to achieve zero-bias photocurrent in two-dimensional (2D) material flakes exploiting the geometrical nonequivalence of source and drain contacts. As a prototypical example, we equip a square-shaped flake of PdSe₂ with mutually orthogonal metal leads. Upon uniform illumination with linearly polarized light, the device demonstrates nonzero photocurrent which flips its sign upon 90° polarization rotation. The origin of zero-bias photocurrent lies in a polarization-dependent lightning-rod effect. It enhances the electromagnetic field at one contact from the orthogonal pair and selectively activates the internal photoeffect at the respective metal-PdSe₂ Schottky junction. The proposed technology of contact engineering is independent of a particular light-detection mechanism and can be extended to arbitrary 2D materials.