A B S T R A C T Hydrothermal zinc oxide (ZnO) nanorod (NR)-based p-Si/n-ZnO and p-Si/i-SiO 2 /n-Z... more A B S T R A C T Hydrothermal zinc oxide (ZnO) nanorod (NR)-based p-Si/n-ZnO and p-Si/i-SiO 2 /n-ZnO heterojunctions were fabricated, and the effects of interfacial native SiO 2 (~4 nm) on the I-V characteristics of heterojunctions under dark and ultraviolet illumination conditions were investigated. First, the structural and optical properties of ZnO seed crystals grown by sol-gel method and hydrothermal ZnO NRs on two different substrates of p-Si and p-Si/i-SiO 2 were examined, and more improved optical and crystalline quality was obtained as revealed by photoluminescence and X-ray diffraction. The p-in heterojunctions showed ~3 times greater forward-bias currents and enhanced rectifying property than those of p-n junctions, which is attributed to the role of native SiO 2 in carrier confinement by promoting the electron-hole recombination current through the deep level states of ZnO crystal. The measured ratios of photocurrent to dark current of the p-in structure were also greater under reverse bias (92–260) and forward bias (2.3–7.1) conditions than those (28–225 for reverse bias, 1.6–6.8 for forward bias) of p-n structure, and the improved photosensitivity of the p-in structure under reverse bias is due to lower density of recombination centers in the ZnO NR crystals. Fabricated ZnO NR heterojunction showed repeatable and fast photo-response transients under forward bias condition of which response and recovery times were 7.2 and 3.5 s for p-in and 4.3 and 1.7 s for p-n structures, respectively.
We present the first active visible blind ultraviolet (UV) photodetector based on zinc oxide (ZnO... more We present the first active visible blind ultraviolet (UV) photodetector based on zinc oxide (ZnO) nanostructured AlGaN/GaN high electron mobility transistors (HEMTs). The ZnO nanorods (NRs) are selectively grown on the gate area by using hydrothermal method. It is shown that ZnO nanorod (NR)-gated UV detectors exhibit much superior performance in terms of response speed and recovery time to those of seed-layer-gated detectors. It is also found that the best response speed (~10 and~190 ms) and responsivity (~1.1×105 A/W) were observed from detectors of the shortest gate length of 2 µm among our NR-gated devices of three different gate dimensions, and this responsivity is about one order higher than the best performance of ZnO NR-based UV detectors reported to date.
A B S T R A C T Hydrothermal zinc oxide (ZnO) nanorod (NR)-based p-Si/n-ZnO and p-Si/i-SiO 2 /n-Z... more A B S T R A C T Hydrothermal zinc oxide (ZnO) nanorod (NR)-based p-Si/n-ZnO and p-Si/i-SiO 2 /n-ZnO heterojunctions were fabricated, and the effects of interfacial native SiO 2 (~4 nm) on the I-V characteristics of heterojunctions under dark and ultraviolet illumination conditions were investigated. First, the structural and optical properties of ZnO seed crystals grown by sol-gel method and hydrothermal ZnO NRs on two different substrates of p-Si and p-Si/i-SiO 2 were examined, and more improved optical and crystalline quality was obtained as revealed by photoluminescence and X-ray diffraction. The p-in heterojunctions showed ~3 times greater forward-bias currents and enhanced rectifying property than those of p-n junctions, which is attributed to the role of native SiO 2 in carrier confinement by promoting the electron-hole recombination current through the deep level states of ZnO crystal. The measured ratios of photocurrent to dark current of the p-in structure were also greater under reverse bias (92–260) and forward bias (2.3–7.1) conditions than those (28–225 for reverse bias, 1.6–6.8 for forward bias) of p-n structure, and the improved photosensitivity of the p-in structure under reverse bias is due to lower density of recombination centers in the ZnO NR crystals. Fabricated ZnO NR heterojunction showed repeatable and fast photo-response transients under forward bias condition of which response and recovery times were 7.2 and 3.5 s for p-in and 4.3 and 1.7 s for p-n structures, respectively.
We present the first active visible blind ultraviolet (UV) photodetector based on zinc oxide (ZnO... more We present the first active visible blind ultraviolet (UV) photodetector based on zinc oxide (ZnO) nanostructured AlGaN/GaN high electron mobility transistors (HEMTs). The ZnO nanorods (NRs) are selectively grown on the gate area by using hydrothermal method. It is shown that ZnO nanorod (NR)-gated UV detectors exhibit much superior performance in terms of response speed and recovery time to those of seed-layer-gated detectors. It is also found that the best response speed (~10 and~190 ms) and responsivity (~1.1×105 A/W) were observed from detectors of the shortest gate length of 2 µm among our NR-gated devices of three different gate dimensions, and this responsivity is about one order higher than the best performance of ZnO NR-based UV detectors reported to date.
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Papers by Waqar Khan