Large bulk photovoltaic effect and spontaneous polarization of single-layer monochalcogenides

TL;DR

This study predicts that single-layer Ge and Sn monochalcogenides exhibit a large bulk photovoltaic effect and spontaneous polarization, making them promising for visible-spectrum polar optoelectronic applications.

Contribution

The paper introduces first-principles calculations of shift current and absorption in these materials, revealing their strong photovoltaic response and linking it to their spontaneous polarization.

Findings

Large shift current (~100 μA/V²) in visible spectrum

Strong absorption in the visible spectrum

Correlation between shift current and spontaneous polarization (~1.9 C/m²)

Abstract

We use a first-principles density functional theory approach to calculate the shift current and linear absorption of uniformly illuminated single-layer Ge and Sn monochalcogenides. We predict strong absorption in the visible spectrum and a large effective three-dimensional shift current ($\sim$100 $\mu$A/V$^2$), larger than has been previously observed in other polar systems. Moreover, we show that the integral of the shift-current tensor is correlated to the large spontaneous effective three-dimensional electric polarization ($\sim$1.9 C/m$^2$). Our calculations indicate that the shift current will be largest in the visible spectrum, suggesting that these monochalcogenides may be promising for polar optoelectronic devices. A Rice-Mele tight-binding model is used to rationalize the shift-current response for these systems, and its dependence on polarization, in general terms with implications for other polar materials