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 .