Enhanced Shift Currents in Monolayer 2D GeS and SnS by Strain-Induced Band Gap Engineering

Abstract

Group IV monochalcogenides exhibit spontaneous polarization and ferroelectricity, which are important in photovoltaic materials. Since strain engineering plays an important role in ferroelectricity, in the present work, the effect of equibiaxial strain on the band structure and shift currents in monolayer two-dimensional (2D) GeS and SnS has systematically been investigated using the first-principles calculations. The conduction bands of those materials are more responsive to strain than the valence bands. Increased equibiaxial compressive strain leads to a drastic reduction in the band gap and finally the occurrence of phase transition from semiconductor to metal at strains of −15 and −14% for GeS and SnS, respectively. On the other hand, tensile equibiaxial strain increases the band gap slightly. Similarly, increased equibiaxial compressive strain leads to a steady almost four times increase in the shift currents at a strain of −12% with direction change occurring at −8% strain. However, at phase transition from semiconductor to metal, the shift currents of the two materials completely vanish. Equibiaxial tensile strain also leads to increased shift currents. For SnS, shift currents do not change direction, just as the case of GeS at low strain; however, at a strain of +8% and beyond, direction reversal of shift currents beyond the band gap in GeS occur.

Large Bulk Piezophotovoltaic Effect of Monolayer 2H-MoS2

“…Several approaches have been studied experimentally to tune the shift current response of a material. The geometry of the sample and electrodesfor example using thin films or single-tip electrodesplays a large role in the magnitude of the BPVE. , Temperature, strain, − and strain gradients , can also significantly modulate the shift current. Applied strain can significantly improve photovoltaic device performance (termed the piezophotovoltaic effect).…”

Atomic configuration controlled photocurrent in van der Waals homostructures

“…However, when an inplane strain is applied, it breaks the C z 3 symmetry of the Bernal stacked bilayers, and as we now discuss, enables a strain induced SPC even for unpolarized light; such strains can be naturally found in many moire material stacks [24]. We note that strain has recently emerged as a tool for controlling bulk photocurrents [34][35][36][37][38][39].…”

Giant Shift Photovoltaic Current in Group V‐V Binary Nanosheets

“…[3,8,16,26] First principle studies predicted enhanced SC; one via electrostatic control in layered ferroelectrics, since charges face a stronger impetus to screen the electric field in thicker materials, [29] and another via application of bi-axial external strain. [32] Similarly, it has been established from an experimental study that the choice of electrodes has a great impact on the extraction of SC, and electrodes with large work function dramatically enhance SC. [22] Enhancing SC is a promising approach for designing of efficient nonlinear optical devices, but the presence of symmetry inversion in most bulk materials limits the choices of such materials to be used in BPVE.…”