Large Bulk Photovoltaic Effect and Spontaneous Polarization of Single-Layer Monochalcogenides

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 (∼100 µA/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 threedimensional electric polarization (∼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

Quantitative relationship between polarization differences and the zone-averaged shift photocurrent

“…Hence, our results provide the long-sought link between electric polarization and shift current injection. There is numerical evidence that 2D ferroelectric single-layer IV-monochalcogenides have large shift current 22,23 . A recent experiment measuring shift current on thin films of GeS is consistent with our results 27 .…”

“…The right-hand-side is gauge invariant and has simple analytical expressions for effective models of monochalcogenides 22,23 . It contains two important physical effects, density of states and the geometry of Bloch wavefunctions.…”

“…23, in real-life applications such as solar cells, the integrated response over a frequency range is more important than the response at a single frequency. Integrating over all frequency,…”

“…In particular, 2D materials have highly tunable electronic and optical properties [17][18][19][20] and are expected to generate large shift current [21][22][23] . We can identify three factors that determine the magnitude of the shift current: density of states, velocity matrix elements and shift-vector matrix elements.…”

Spatio-temporal dynamics of shift current quantum pumping by femtosecond light pulse

“…However, photocurrent generated by BPVE in a closed circuit remains small compared to pn-junctions. This has ignited renewed experimental [4,[6][7][8][9][10][11] and theoretical [12][13][14][15][16][17][18] interest in BPVE with the ultimate goal [15] to optimize its power conversion efficiency.…”