Abstract
This paper focuses on amorphous silicon photo thin-film transistors with double layered insulator using Si 3 N 4 /Al 2 O 3 or HfO 2 as candidates for the succession of Si 3 N 4 as a traditional insulator in the fabrication of hydrogenated amorphous silicon thin-film transistors. Whether for industry or for research, there is a need to investigate the use of thin gate insulators for these devices to overcome leakage current. Our investigations included direct and transfer characteristics in dark and under illumination, generated photocurrents, external quantum efficiency and responsivity. Performance is evaluated in terms of the dielectric thickness and nature. Improvements in the proposed structures regarding off-current, responsivity and quantum efficiency are achieved via these materials. Comparing with Si 3 N 4 /HfO 2 transistor, the Si 3 N 4 /Al 2 O 3 device shows the lowest off-current. The HfO 2 device presents the highest on-current when illuminated. The generated photocurrent is higher for Si 3 N 4 /HfO 2 transistor revealing a lower amount of trapped charge. Under illumination and for very thin thicknesses, both devices enhance the Si 3 N 4 device off-current and reach Si 3 N 4 single layer dielectric based phototransistor performance. external quantum efficiency and responsivity are higher in HfO 2 devices comparing with Al 2 O 3 devices. The results are promising and may support further investigations in order to develop high k gate insulators for MIS photo thin-film transistors.
Highlights
Amorphous silicon thin film transistor (a-Si:H TFT) technology is receiving more consideration due its wider applications
An amorphous silicon photo TFT (APT) with Si3N4/Al2O3 or HfO2 double layered insulator for digital imaging applications is investigated in order to optimize detectors characteristics
For 30 nm thickness of Al2O3 and HfO2, the results show that under illumination by 420 nm wavelength, even the offcurrent is minimum for APT2, the use of HfO2 as a second insulating layer gives higher on-current
Summary
Amorphous silicon thin film transistor (a-Si:H TFT) technology is receiving more consideration due its wider applications. The utilization of amorphous silicon TFT is dictated by some advantages like simple fabrication process, high charge transfer rate, low capacitance, high photo-sensitivity and low noise [1]-[3]. In digital radiography, this technology allowed the at panel detectors (FPDs) to be commercially available for many kinds of medical imaging detectors. An amorphous silicon photo TFT (APT) with Si3N4/Al2O3 or HfO2 double layered insulator for digital imaging applications is investigated in order to optimize detectors characteristics. The paper is organized as follows: Section II describes the adopted APTs structures, Section III illustrates the obtained results, while Section IV concludes the paper
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