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

Structural or crystal asymmetry is a necessary conditionfor theemergence of zero-bias photocurrent in light detectors. Structuralasymmetry has been typically achieved via p-n doping, whichis a technologically complex process. Here, we propose an alternativeapproach to achieve zero-bias photocurrent in two-dimensional (2D)material flakes exploiting the geometrical nonequivalence of sourceand drain contacts. As a prototypical example, we equip a square-shapedflake of PdSe2 with mutually orthogonal metal leads. Uponuniform illumination with linearly polarized light, the device demonstratesnonzero photocurrent which flips its sign upon 90 degrees polarizationrotation. The origin of zero-bias photocurrent lies in a polarization-dependentlightning-rod effect. It enhances the electromagnetic field at onecontact from the orthogonal pair and selectively activates the internalphotoeffect at the respective metal-PdSe2 Schottky junction.The proposed technology of contact engineering is independent of aparticular light-detection mechanism and can be extended to arbitrary2D materials.