A visible-light phototransistor based on the heterostructure of ZnO and TiO2 with trap-assisted photocurrent generation |
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Authors: | Byung Jun Kim Jun Hyung Jeong Eui Young Jung Tae Yeon Kim Sungho Park Jong-Am Hong Kyu-Myung Lee Woojin Jeon Yongsup Park Seong Jun Kang |
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Institution: | Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Yongin 17104 Republic of Korea, +82-31-201-3324 ; Integrated Education Program for Frontier Materials (BK21 Four), Kyung Hee University, Yongin 17104 Republic of Korea ; Department of Physics and Research Institute for Basic Sciences, Kyung Hee University, Seoul 02447 Republic of Korea ; Department of Information Display, Kyung Hee University, Seoul 02447 Republic of Korea |
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Abstract: | Visible-light phototransistors have been fabricated based on the heterojunction of zinc oxide (ZnO) and titanium oxide (TiO2). A thin layer of TiO2 was deposited onto the spin-coated ZnO film via atomic layer deposition (ALD). The electrical characteristics of the TiO2 layer were optimized by controlling the purge time of titanium isopropoxide (TTIP). The optimized TiO2 layer could absorb the visible-light from the sub-gap states near the conduction band of TiO2, which was confirmed via photoelectron spectroscopy measurements. Therefore, the heterostructure of TiO2/ZnO can absorb and generate photocurrent under visible light illumination. The oxygen-related-states were investigated via X-ray photoelectron spectroscopy (XPS), and the interfacial band structure between TiO2 and ZnO was evaluated via ultraviolet photoelectron spectroscopy (UPS). Oxygen-related states and subgap-states were observed, which could be used to generate photocurrent by absorbing visible light, even with TiO2 and ZnO having a wide bandgap. The optimized TiO2/ZnO visible-light phototransistor showed a photoresponsivity of 99.3 A W−1 and photosensitivity of 1.5 × 105 under the illumination of 520 nm wavelength light. This study provides a useful way to fabricate a visible-light phototransistor based on the heterostructure of wide bandgap oxide semiconductors.Visible-light phototransistors have been fabricated based on the heterojunction of zinc oxide (ZnO) and titanium oxide (TiO2). |
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