Ultraviolet photodetectors based on Si-Zn-SnO thin film transistors with a stacked channel structure and a patterned NiO capping layer

Abstract

Ultraviolet photodetectors (UVPDs) based on Si-Zn-SnO (SZTO) thin-film transistors (TFTs) with a stacked dual-channel layer (DCL) structure with different carrier concentration and NiO capping layer (CL) to alleviate the trade-off between dark current (I dark) and photocurrent (I ph) are reported. Experimental results show that under 275 nm irradiation, the proposed SZTO TFT UVPD with a 30-nm-thick upper layer stacked on a 50-nm-thick channel layer and a patterned NiO CL exhibit excellent photoresponsivity and photosensitivity up to 1672 A/W and 1.03×107 A/A, which is about 272 and 137 times higher than conventional 30-nm-thick single-channel layer SZTO TFT. These improvements are due to the use of DCL forms a high-low junction to reduce the effective channel thickness and increase the space for UV illumination and the use of NiO CL lowers the I dark and causes a considerable negative threshold voltage shift under UV irradiation to significantly boost the I ph.

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

“…More information about the TFT manufacturing process can be found in our previous report. 28) To achieve complete depletion of the channel layer to suppress I dark in the thick channel layer, patterned Pt CL, NiO CL, or stacked Pt/NiO dual CLs were deposited on the top surface of the SZTO channel layer. According to a material analysis based on transmittance spectra, Tauc plots, Hall measurements, and UV photoelectron spectroscopy (UPS), it is estimated that Pt CL and NiO CL produce depletion layer widths (W dc ) of about 50 nm and 15 nm, respectively, on the SZTO channel.…”

“…In this case, I ph is suppressed because the space available for carrier generation is limited and the channel resistance is high. [19][20][21] Reducing the carrier concentration (n) in the channel layer of TFT based UVPDs, or using a Schottky metals (e.g., Pt, 22,23) Au, 24) and Ni 25) ), or p-type MOSs (e.g., NiO, [26][27][28] MgO, 29) and Cr 2 O 3 30) ) as a capping layer (CL) on the channel surface (i.e. the back channel) have been demonstrated to mitigate the trade-off between I dark and I ph .…”

“…Oxygen has been commonly introduced to MOSs to lower carrier concentration and improve the reliability of device applications such as TFTs. 28,[31][32][33][34] Using a Schottky metal CL with a high work function 35,36) enables one to maximize the width of the depletion region (W dc ) on the channel layer, as it shares almost all the voltage drop caused by the difference in work function between the CL and the channel layer. However, the opacity of the Schottky metal prevents incident light from entering the channel area below, which requires the Schottky metal CL's area to be minimized.…”

“…However, the opacity of the Schottky metal prevents incident light from entering the channel area below, which requires the Schottky metal CL's area to be minimized. In contrast, a CL that utilizes a p-type oxide semiconductor with a wider energy bandgap 28,37,38) forms a pn heterojunction (HJ) with the channel layer, and the incident light is not blocked. Although the W dc generated within the channel layer is narrower than with Schottky metal, the entire depletion region is wider and more suitable for carrier generation and collection.…”

“…Although the W dc generated within the channel layer is narrower than with Schottky metal, the entire depletion region is wider and more suitable for carrier generation and collection. 27,28) Therefore, it is necessary to maximize its area.…”