Anisotropic Photostriction and Strain-modulated Carrier Lifetimes in Orthorhombic Semiconductors

TL;DR

This study reveals how anisotropic photostriction in 2D orthorhombic semiconductors can be controlled by light, affecting lattice structure and carrier lifetimes, with implications for nanoscale optomechanical devices.

Contribution

It provides a microscopic understanding of anisotropic photostriction and demonstrates tunable strain effects on carrier dynamics in layered semiconductors.

Findings

Lattice expands along armchair and contracts along zigzag directions.

Photodoping tunes the magnitude and orientation of strains.

Photoinduced strains increase carrier recombination lifetimes.

Abstract

We demonstrate anisotropic photostriction in two-dimensional orthorhombic semiconductors using time-dependent density functional theory. By tracing the dynamics of photoexcited carriers, we establish a quantitative link between carrier density and lattice deformation in layered black phosphorus and germanium selenides. The structural response exhibits significant anisotropy, featuring lattice expansion along the armchair direction and contraction along the zigzag direction, which is attributed to the interplay between charge redistribution and intrinsic lattice anisotropy. Both the magnitude and orientation of the photostrictive strains can be tuned by photodoping densities, enabling precise control over the photoinduced response. Notably, the photoinduced strains significantly increase carrier recombination lifetimes by suppressing nonradiative recombination, primarily due to the enlarged bandgap and weakened nonadiabatic coupling. These results provide microscopic insight into the origin of anisotropic photostriction in low-dimensional systems and lay the groundwork for light-controllable, directionally sensitive optomechanical devices at the atomic scale.