Performance Improvement of TiO 2 Ultraviolet Photodetectors by Using Atomic Layer Deposited Al 2 O 3 Passivation Layer.

This study employed atomic layer deposition (ALD) to fabricate an Al ₂ O ₃ passivation layer to optimize the performance of ultraviolet (UV) photodetectors with a TiO ₂ -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 TiO ₂ -NR-containng working electrode. Subsequently, a 5-nm-thick Al ₂ O ₃ passivation layer was deposited on the TiO ₂ NRs through ALD, which has excellent step coverage, to reduce the surface defects in the TiO ₂ NRs and improve the carrier transport efficiency. X-ray photoelectron spectroscopy revealed that the aforementioned layer reduced the defects in the TiO ₂ NRs. Moreover, high-resolution transmission electron microscopy indicated that following the annealing treatment, Al, Ti, and O atoms diffused across the interface between the Al ₂ O ₃ passivation layer and TiO ₂ NRs, resulting in the binding of these atoms to form Al-Ti-O bonds. This process effectively filled the oxygen vacancies in TiO ₂ . 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 Al ₂ O ₃ passivation layer deposited through ALD can enhance the photodetection performance of SLHJ UV photodetectors with a TiO ₂ active layer.