Strain engineering of anisotropic light–matter interactions in one-dimensional P–P chain of SiP₂

Strain engineering can serve as a powerful technique for modulating the exotic properties arising from the atomic structure of materials. Examples have been demonstrated that one-dimensional (1D) structure can serve as a great platform for modulating electronic band structure and phonon dispersion via strain control. Particularly, in a van der Waals material silicon diphosphide (SiP₂), quasi-1D zigzag phosphorus–phosphorus (P–P) chains are embedded inside the crystal structure, and can show unique phonon vibration modes and realize quasi-1D excitons. Manipulating those optical properties by the atom displacements via strain engineering is of great interest in understanding underlying mechanism of such P–P chains, however, which remains elusive. Herein, we demonstrate the strain engineering of Raman and photoluminescence (PL) spectra in quasi-1D P–P chains and resulting in anisotropic manipulation in SiP₂. We find that the phonon frequencies of SiP₂ in Raman spectra linearly evolve with a uniaxial strain along/perpendicular to the quasi-1D P–P chain directions. Interestingly, by applying tensile strain along the P–P chains, the band gap energy of strained SiP₂ can significantly decrease with a tunable value of ~ 55 meV. Based on arsenic (As) element doping into SiP₂, the strain-induced redshifts of phonon frequencies decrease, indicating the stiffening of the phonon vibration with the increased arsenic doping level. Such results provide an opportunity for strain engineering of the light–matter interactions in the quasi-1D P–P chains of SiP₂ crystal for potential optical applications.