Deep and weak ultraviolet photodetection on micro-nanotextured black silicon with Al₂O₃ film

A weak UV detection device is proposed in this work that utilizes a combination of the large specific surface area of micro-nanotextured black silicon and high negative charge density Al ₂ O ₃ . Black silicon is fabricated by two etching steps consist of Bosch etching and reactive ion etching. The absorption of black silicon increases up to 99.7%, which is reduced by 0.9% after Al ₂ O ₃ films are deposited. The 20 nm Al ₂ O ₃ film is deposited by atomic layer deposition(ALD) to ensure its quality and conformality. The external quantum efficiency (EQE) of the device is obtained to be greater than 80%, with the responsivity being higher than 170% at 200-255 nm. Notably, at 200 nm, the EQE reaches 162%, and the corresponding responsivity is found to be 262 mA/W. The photoelectric properties are characterized under intense and weak ultraviolet light, respectively. And the device demonstrates the good detection ability and fast response to weak UV light. Under illumination of weak light of different wavelengths at 220, 325, 405 nm under zero bias, the current of the device increases from 0.15 μA to 9.4 μA. The rise time(τ _r ) and the decay time(τ _d ) of device under weak UV light illumination(325nm) at the reverse voltage of 0V are estimated to be 0.3 s and 0.29 s. The power intensity(PI) of 325nm wavelength is 2.57 μW/cm ² . Thus, the proposed detection strategy enables weak UV photodetection in missile warning and environmental monitoring.