Room Temperature Anisotropic Photoresponse in Low-Symmetry van der Waals Semiconductor CrPS${}_4$

Abstract

The crystalline and optical anisotropy of low-symmetry two-dimensional (2D) materials can enable strong dichroic responses, enhancing polarization contrast for photonic and optoelectronic devices. Here, we unveil pronounced optical and optoelectronic anisotropy in chromium thiophosphate CrPS${}_4$ arising from the strong coupling between light polarization and its intrinsic crystal symmetry. Linearly polarized reflectivity and scanning photocurrent measurements in the 1.37-2.48 eV range reveal a robust dichroic response. The linear dichroism in reflection RLD reaches ~50, while in photocurrent PCLD it increases to ~60, with a sign reversal of the RLD between 1.6-1.8 eV, enabling strong narrow-band polarization contrast at room temperature. We attribute these anisotropic responses to the interaction between polarized light and Cr${}^{3+}$ d-orbital T${}_1$ and T${}_2$ transitions. Spatially resolved photocurrent mapping further shows that the photocurrent is strongly dependent on the crystallographic axis: a 3-fold enhancement is obtained along the b-axis compared to the a-axis, yielding a clear 180° modulation of photoresponse across different contact orientations. Together, our findings establish CrPS${}_4$ as a highly anisotropic 2D semiconductor with strong linear dichroism and polarization-sensitive photoresponse at room temperature. These characteristics highlight CrPS4 as a promising platform for narrow-band polarized photodetectors, anisotropic photo-transport, and future 2D spintronic and magneto-optical devices.

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