Defects‐Induced Linear Dichroism in Anisotropic Layered SiP₂

Linear dichroism emerging from anisotropic band structures in semiconductors plays a significant role for optoelectronic applications. Lattice defects in low‐dimensional anisotropic semiconductors can induce defect states within the electronic bandgap, resulting in linearly dichroic light absorption or emission. Here, the defect‐induced dual‐channel linear dichroism in layered silicon diphosphide is demonstrated, in which the intrinsic exciton peak (2.06 eV) hosts a linear polarization along the x direction of the lattice, while the polarization of the defect state emissions (1.6 and 1.4 eV) is perpendicular to the x direction. Combining photoluminescence measurements with the first‐principles calculations, the lower‐energy photoluminescence peaks are attributed to specific composite defects, such as the one composed of a phosphorus substitutional defect on a silicon site and a phosphorus vacancy. These defects can induce localized in‐gap deep states near the valence band maximum with highly anisotropic wavefunction, contributing to the observed linear dichroism. Notably, as the sample thickness decreases, the defect‐induced photoluminescence becomes weaker. This observation of dual‐channel linear dichroism in silicon diphosphide provides a new material platform for light polarization modulation and optoelectronic devices.