Bulk photovoltaic effect and high mobility in the polar 2D semiconductor SnP 2 Se 6 .

The growth of layered 2D compounds is a key ingredient in finding new phenomena in quantum materials, optoelectronics, and energy conversion. Here, we report SnP ₂ Se ₆ , a van der Waals chiral ( R 3 space group) semiconductor with an indirect bandgap of 1.36 to 1.41 electron volts. Exfoliated SnP ₂ Se ₆ flakes are integrated into high-performance field-effect transistors with electron mobilities >100 cm ² /Vs and on/off ratios >10 ⁶ at room temperature. Upon excitation at a wavelength of 515.6 nanometer, SnP ₂ Se ₆ phototransistors show high gain (>4 × 10 ⁴ ) at low intensity (≈10 ^-6 W/cm ² ) and fast photoresponse (< 5 microsecond) with concurrent gain of ≈52.9 at high intensity (≈56.6 mW/cm ² ) at a gate voltage of 60 V across 300-nm-thick SiO ₂ dielectric layer. The combination of high carrier mobility and the non-centrosymmetric crystal structure results in a strong intrinsic bulk photovoltaic effect; under local excitation at normal incidence at 532 nm, short circuit currents exceed 8 mA/cm ² at 20.6 W/cm ² .