High-performance WSe2 Geiger avalanche photodetector from 405 to 808 nm

Avalanche photodiodes are attractive for weak-light detection. However, conventional avalanche devices usually suffer from high breakdown voltage, large dark current, and a limited gain–noise trade-off, restricting their applications in low-power and ultrasensitive photodetection. Here, we report a Pt/WSe2/graphene asymmetric Schottky diode that exhibits bilateral Geiger-mode avalanche operation. It shows abrupt avalanche breakdown under both positive and negative biases, with room-temperature breakdown voltages of approximately +19.6 and −23.45 V, respectively. Owing to the asymmetric Schottky barriers and bias-induced band bending in ambipolar WSe2, the carrier injection terminal and high-field multiplication region can be switched by the bias polarity, enabling bilateral impact ionization in a two-terminal geometry. Temperature-dependent investigations from 100 to 300 K confirm stable bilateral avalanche operation, with the breakdown voltage increasing at lower temperatures due to the modulation of carrier acceleration and scattering. Under femtowatt-level illumination at room temperature, photogenerated carriers facilitate impact ionization and shift the avalanche threshold toward lower bias. The device exhibits avalanche gains of 1.11 × 105 and 1.25 × 104 under negative and positive bias, respectively, and enables weak-light detection over 405–808 nm. At 808 nm, the responsivity reaches 107 A W−1 and the specific detectivity reaches 1014 Jones. This work demonstrates that asymmetric Schottky-contact engineering combined with ambipolar WSe2 transport provides an effective strategy for high-gain, high-detectivity, and bidirectional two-dimensional avalanche photodetectors.