Deep and Weak Ultraviolet Photodetection on Micro-Nano Textured Black Silicon With Al2O3 Film

A weak ultraviolet (UV) detection device is proposed in this work that utilizes a combination of the large specific surface area of micro-nano textured black silicon and high negative charge density Al2O3. Black silicon is fabricated by two etching steps that 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 Al2O3 films are deposited. The 20-nm Al2O3 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 UV light, respectively. Also, 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, and 405 nm under zero bias, the current of the device increases from 0.15 to $9.4~\mu $ A. The rise time ( $\tau _{r}$ ) and the decay time ( $\tau _{d}$ ) of device under weak UV light illumination (325 nm) at the reverse voltage of 0 V are estimated to be 0.3 and 0.29 s. The power intensity (PI) of 325-nm wavelength is $2.57~\mu $ W/cm2. Thus, the proposed detection strategy enables weak UV photodetection in missile warning and environmental monitoring.