Theoretical and Experimental Analysis of Amorphous Silicon Image Sensor
- PDF / 832,536 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 6 Downloads / 232 Views
THEORETICAL AND EXPERIMENTAL ANALYSIS OF AMORPHOUS SILICON IMAGE SENSOR Chih-Yuang Su, Ying-Wen Su and Huey-Liang Hwang Department of Electrical Engineering, National Tsing Hua University, Hsinchu, Taiwan 30043, R. 0. C. Abstract The experimental results for different structures of contact image sensor are reported in this paper, which includes Schottky barrier, p-i junction, p-i-n junction, and MIS structures. The J-Vcharacteristics of p-i-n a-Si: H contact image sensor under dark and illuminated conditions have been simulated by solving the Poisson's equation and the continuity equations, and the results are correlated with the experiments. The dependence of the dark and photo currents on the parameters such as the density of states in the gap, intrinsic layer width, dopant concentrations of p+ layer and n+ layer are discussed. Introduction In the last few years much progress has been made with a-Si:H contact image sensor (CIS) . The technologies are now in mature state [1, 2], but the reports on detailed analysis have been lacked. The a-Si:H samples used in this study for different structures of CIS are prepared by RF glow-discharged decomposition of SiH4 , and they are doped with phosphorus or boron in different concentrations. Metal like Al, Cr, Ti are evaporated by an electron beam gun. The ITO layer is prepared by the CVD technique. The detailed experimental work has been reported elsewhere [3]. In our work the J-V characteristics of the p-i-n junction are analyzed by a numerical scheme and their dependence on the density of states in the energy gap, and the dopant concentrations are studied. The transport mechanism for p-i-n devices have been treated by a number of investigations [4-8]. Our simulation model is based on solving self-consistently the Poisson's equation and the continuity equations. 1.
2.
Experimental results
The Schottky barrier diode has the simplest structure. The blocking effect of this diode is mainly due to the potential barrier at the ITO and the photosensitive a-Si :H interface. It exhibits a photo-todark current ratio of approximating 103, as shown in Fig. 1(a) . The p-i (hetero) junction photodiode also has a simple structure. Because the blocking effect is due to the growing junction formed in the one pump down system, the sensor shows stable characteristics and has a photo-to-dark current ratio as high as 104, as shown in Fig. 1(b) . In the MIS photodiode, electron-hole pairs are generated near the interface between the Si 3 N4 and the i-a-Si: H layer, and are drifted by the applied voltage, and that passes through the blocking layer. The photo-to-dark current ratio is as high as 105, as shown in Fig. 1(d). This fact clearly indicates that the Si 3 N4 layer effectively blocks the holes injecting from the electrode. The p-i-n junction photodiode is the most stable structure. In this structure, junctions are grown for both the top and bottom contacts. However, its fabrication process is relatively complicated, because the highly conductive bottom n layer must be etched to divide t
Data Loading...
