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

TL;DR

This study demonstrates that CrPS$_4$, a low-symmetry 2D semiconductor, exhibits strong room-temperature anisotropic optical and photoresponse properties, making it promising for polarized photodetectors and spintronic applications.

Contribution

The paper reveals pronounced optical and optoelectronic anisotropy in CrPS$_4$, including strong dichroic responses and polarization-dependent photocurrent, driven by light-crystal symmetry interactions.

Findings

Linear dichroism in reflection reaches ~50%

Photocurrent dichroism increases to ~60% with sign reversal

Photocurrent shows 3-fold enhancement along the b-axis

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{\deg} 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.