Performance Improvement of TiO2 Ultraviolet Photodetectors by Using Atomic Layer Deposited Al2O3 Passivation Layer

This study employed atomic layer deposition (ALD) to fabricate an Al2O3 passivation layer to optimize the performance of ultraviolet (UV) photodetectors with a TiO2-nanorod-(NR)-containing active layer and a solid-liquid heterojunction (SLHJ). To reduce the processing time and enhance light absorption, a hydrothermal method was used to grow a relatively thick TiO2-NR-containng working electrode. Subsequently, a 5-nm-thick Al2O3 passivation layer was deposited on the TiO2 NRs through ALD, which has excellent step coverage, to reduce the surface defects in the TiO2 NRs and improve the carrier transport efficiency. X-ray photoelectron spectroscopy revealed that the aforementioned layer reduced the defects in the TiO2 NRs. Moreover, high-resolution transmission electron microscopy indicated that following the annealing treatment, Al, Ti, and O atoms diffused across the interface between the Al2O3 passivation layer and TiO2 NRs, resulting in the binding of these atoms to form Al-Ti-O bonds. This process effectively filled the oxygen vacancies in TiO2. Examination of the photodetector device revealed that the photocurrent-to-dark current ratio exhibited a difference of four orders of magnitude (10(-4) to 10(-8) A), with the switch-on and switch-off times being 0.46 and 3.84 s, respectively. These results indicate that the Al2O3 passivation layer deposited through ALD can enhance the photodetection performance of SLHJ UV photodetectors with a TiO2 active layer.