Bulk photovoltaic effect and high mobility in the polar 2D semiconductor SnP₂Se₆

Layer-dependent properties of van der Waals (vdW) semiconductors combined with artificially engineered symmetry and interfaces in vdW heterostructures have led to a wide range of optoelectronic applications including photodetectors and photovoltaics. For example, the bulk photovoltaic effect (BPVE) requires a non-centrosymmetric material with a strong polarity to produce photocurrent without geometrical asymmetries. While mono-elemental and binary vdW materials show weak intrinsic polarity for BPVE, layered ternary and quaternary compounds such as chalcophosphate present new material systems with a greater number of compositions as semiconductors, ferroelectric, magnetic, and nonlinear optical crystals. In this talk, I will discuss the properties of a newly synthesized layered SnP₂Se₆ crystal, a van der Waals chiral (R3 space group) semiconductor with an indirect bandgap of ≈1.4 eV.^[1] SnP₂Se₆ flakes were integrated into high-performance field-effect transistors with electron mobilities >100 cm²/Vs and on/off ratios >10⁶ at room temperature. SnP₂Se₆ phototransistors show high gain (>10⁴) and fast photoresponse (<5 μs) at a wavelength of 515.6 nm. High mobility and polarity result in a strong intrinsic BPVE resulting in a short circuit current of 8 mA/cm² at 20.6 W/cm². A systematic study of spatially-, spectrally- and angle-resolved photocurrent measurements rules out competing mechanisms and agrees with a phenomenological shift current model.^[1]

[1] Science Advances 10, eado8272 (2024)