Anisotropic photogalvanic effects in monolayer WSe₂ under elliptically polarized light

We investigate the photogalvanic effect in monolayer WSe₂ under elliptically polarized light using non-equilibrium Green’s function density functional theory (NEGF-DFT) simulations. When defects are added that reduce the intrinsic D_3h symmetry to C_s and C_2v, the photocurrent shows distinct direction-dependent responses: a sine function of the helicity angle along the zigzag direction and a cosine function along the armchair direction. This anisotropy arises from the specific nonzero tensor elements activated by symmetry reduction. Ga substitution is identified as a highly effective strategy, enhancing the polarization sensitivity by 55.54 times compared to that of pristine WSe₂. Furthermore, we reveal a resonant enhancement mechanism via impurity states introduced by Ga doping, as confirmed by projected density of states (PDOS) analysis. The application of a small bias voltage (0.04 V) further boosts the photocurrent by up to 368 times. These findings establish a direct link between crystal symmetry, defect engineering, and photoresponse, providing a pathway for high-performance polarization-sensitive optoelectronic devices.