Enhancing photodetection performance of UV photodetectors with stacked Pt/NiO dual capping layers on IGZO thin-film transistors

This paper proposes a solution to mitigate the trade-off between dark and photocurrents in the indium gallium zinc oxide (IGZO) thin-film transistor (TFT) applications, such as ultraviolet photodetectors, by using a stacked Pt/NiO dual capping layer (CL). The Pt CL forms a Schottky contact with the IGZO channel, which maximizes the depletion width on the channel layer and allows the use of a thicker channel to suppress both dark current and channel resistance. On the other hand, the NiO CL forms a pn heterojunction with the IGZO channel, which provides additional space for generating electron-hole pairs and is forward biased by the photovoltaic voltage under UV irradiation, resulting in a further negative shift in the threshold voltage and a significant increase in photocurrent. Experimental results show that the proposed CL scheme exhibits excellent photoresponsivity, photosensitivity, and specific detectivity in a 40 nm-thick IGZO TFT, with the values of 1888 A/W, 3.37 × 10⁸ A/A, and 3.99 × 10¹⁶ Jones, respectively, which are about 55%, 83%, and 68% higher than a traditional 30 nm-thick IGZO TFT using only NiO CL under 275 nm UV irradiation.