Study on the mechanism of enhancing photocurrent in TiS2 photodetector by vacancy- and substitution-doping

In materials lacking spatial inversion symmetry, the photovoltaic generation effect (PGE) manifests under polarized irradiation without the necessity of a p-n junction and demonstrates high polarization sensitivity across a broad spectrum. This characteristic presents significant potential for applications in low-power two-dimensional optoelectronic devices. In this study, we investigate the electronic structure, optical properties, and PGE in 2H-TiS2 by first-principles simulations, incorporating various types of point defects. We propose a mechanism to enhance photoconductivity in 2H-TiS2 by substitution doping and vacancy defects. When the photodetector is aligned along the armchair direction, the photocurrent exhibits a cosine dependency on the linear polarization angle. We achieved a remarkable enhancement in photocurrent, with a maximum value of 1.33 a20/photon, in contrast to only 0.11 a20/photon for the pure membrane. This improvement can be attributed to the introduction of point defects, which diminish the symmetry of the device and increase its asymmetry, thereby enhancing the photocurrent. Furthermore, we attained high polarization sensitivity, evidenced by a maximum extinction ratio of 262.4. Our findings not only propose an effective mechanism for enhancing PGE by substitution doping but also underscore the promising applications of the two-dimensional 2H-TiS2 monolayer in optoelectronics, particularly in photoelectric detection.