A visible-light phototransistor based on the heterostructure of ZnO and TiO2 with trap-assisted photocurrent generation

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

doi:10.1039/d1ra00801c

A visible-light phototransistor based on the heterostructure of ZnO and TiO₂ with trap-assisted photocurrent generation

RSC Adv. 2021 Mar 24;11(20):12051-12057. doi: 10.1039/d1ra00801c. eCollection 2021 Mar 23.

Authors

Byung Jun Kim^{1

2}, Jun Hyung Jeong^{1

2}, Eui Young Jung^{1

2}, Tae Yeon Kim^{1

2}, Sungho Park^{1

2}, Jong-Am Hong³, Kyu-Myung Lee³, Woojin Jeon^{1

2}, Yongsup Park^{3

4}, Seong Jun Kang^{1

2}

Affiliations

¹ Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University Yongin 17104 Republic of Korea junkang@khu.ac.kr +82-31-201-3324.
² Integrated Education Program for Frontier Materials (BK21 Four), Kyung Hee University Yongin 17104 Republic of Korea.
³ Department of Physics and Research Institute for Basic Sciences, Kyung Hee University Seoul 02447 Republic of Korea.
⁴ Department of Information Display, Kyung Hee University Seoul 02447 Republic of Korea.

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.