High Performance Avalanche Photodiodes from Bi₂O₂Se

Layered semiconductors consisting of van der Waals and non-van der Waals stacking promise high-performance optoelectronics due to their high mobility, strong light-matter interaction, gate-tunability, and strong in-plane and valley anisotropy. Here, we present metal-semiconductor-metal avalanche photodiodes (APDs) fabricated from layered Bi₂O₂Se crystals, which consist of alternating [Bi₂O₂]²⁺ and [Se]^2- layers that are held together by electrostatic interactions. An efficient inverse Auger process yields an intrinsic carrier multiplication factor up to 400 at 7 K under optical excitation at a wavelength of 515.6 nm, resulting in photodiodes with a responsivity gain in excess of 3,000 A/W at a bandwidth of ~400 kHz. Furthermore, exceptionally low dark currents (200 pA) result in high detectivities as high as 4.6 x 10¹⁴ Jones. The physics that underlies this superlative performance is elucidated by the temperature and bias dependence of carrier multiplication in reverse-biased Schottky diodes (barrier ≈ 44 meV) with InSe deformation potential of 27 – 33 eV. In contrast with charge trap-based extrinsic gain in phototransistors, the intrinsic gain in Bi₂O₂Se APDs paves the way for high-speed and low-noise photodetectors.