Low symmetric sub-wavelength array enhanced lensless polarization-sensitivity photodetector of germanium selenium.

Polarization-sensitive photodetectors, with the ability of identifying the texture-, stress-, and roughness-induced light polarization state variation, displace unique advantages in the fields of national security, medical diagnosis, and aerospace. The utilization of in-plane anisotropic two-dimensional (2D) materials has led the polarization photodetector into a polarizer-free regime, and facilitated the miniaturization of optoelectronic device integration. However, the insufficient polarization ratio (usually less than 10) restricts the detection resolution of polarized signals. Here, we designed a sub-wavelength array (SWA) structure of 2D germanium selenium (GeSe) to further improve its anisotropic sensitivity, which boosts the polarized photocurrent ratio from 1.6 to 18. This enhancement comes from the combination of nano-scale arrays with atomic-scale lattice arrangement at the low-symmetric direction, while the polarization-sensitive photoresponse along the high-symmetric direction is strongly suppressed due to the SWA-caused depolarization effect. Our mechanism study revealed that the SWA can improve the asymmetry of charge distribution, attenuate the matrix element in zigzag direction, and the localized surface plasma, which elevates the photo absorption and photoelectric transition probability along the armchair direction, therefore accounts for the enhanced polarization sensitivity. In addition, the photodetector based on GeSe SWA exhibited a broad power range of 40 dB at a near-infrared wavelength of 808 nm and the ability of weak-light detection under 0.1 LUX of white light (two orders of magnitude smaller than pristine 2D GeSe). This work provides a feasible guideline to improve the polarization sensitivity of 2D materials, and will greatly benefit the development of polarized imaging sensors.