Using thin-film transistor with thick oxygen-doped Si-Zn-Sn-O channel and patterned Pt/NiO capping layer to enhance ultraviolet light sensing performance

Improving the photodetection performance of thin-film transistor (TFT)-based UV photodetectors (UVPDs), using thick channel layers to promote photocurrent (I_ph) or using thin channel layers to suppress dark current (I_dark) is typically a trade-off. In this work, UVPDs based on oxygen-doped Si-Zn-Sn-O (SZTO) TFT with a stack of Pt/NiO capping layers (CLs) to release the trade-off between I_dark and I_ph are demonstrated. The Pt CL creates a wide depletion region in the channel layer to allow the use of thick channels, but still maintains low I_dark, while the NiO CL forms a pn heterojunction to provide additional photogenerated carriers and enhance I_ph under UV irradiation. Experimental results show that the proposed 95 nm-thick oxygen-doped SZTO TFT with a stack of Pt/NiO dual CLs exhibits an excellent photoresponsivity of 2026 A W⁻¹ and photosensitivity of 9.3 × 10⁷ A A⁻¹, which are about 76× and 82.5× higher than a conventional 45 nm-thick SZTO TFT under 275 nm UV irradiation.