Characterization of A-Si: H and A-SiGe: H Films in Liquid Crystal Light Valve
- PDF / 294,529 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 45 Downloads / 148 Views
CHARACTERIZATION OF A-Si: H AND A-SiGe: H FILMS IN LIQUID CRYSTAL LIGHT VALVE Jianmin QIAO. Gaorong HAN, Piyi DU, Weiqiang HAN, Wanquan Huang and Zishang DING Department of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, China ABSTRACT A-Si: H and a-Si: H/a-SiGe: H heterojunctions have been prepared as the photoconductors in the liquid crystal light valves. The impedance matching conditions of the a-Si: H and the heterojunction in the valves have been carefully analysed, which has shown that the adjustment for the capacitance of the photoconductor is the key procedure for the matching, but the low photocapacitance effect in the a-Si: H limits the further improvements on the matching. The formation of the a-Si: H/a-SiGe: H diode promotes the photocapacitance effect in the photoconductor, and the matching behavior in the valve is greatly improved. INTRODUCTION Hydrogenated amorphous silicon thin film (a-Si: H) has been proven to be an attractive material as a photoconductor in the liquid crystal light valve (LCLV)[1,2], in which the light modulation behaviors, such as the spatial resolution, time response and light sensitivity et al., are the main factors to influence the performance of the display system[3]. Great efforts to improve these parameters have been made during the past decade, which have shown the photoconductor in the LCLV played an important role in the device. Until now, the photoconductor has typically used the CdS/CdTe heterojunction[4), c-Si[5], a-Si: H[6] and a-Si: H PIN photodiode(7]. Although cadmium sulfide allows for a reasonable spatial resolution, it is relatively slow and has a narrow wavelength sensitivity, making its overall white light sensitivity low. C-Si has a better sensitivity and high speed but because of its inherent large thickness, its spatial resolution is low. A-Si: H has a high light absorption in the white region, which makes the photoconductor thinner, and keeps a high speed and sensitivity of c-Si. The good matching condition of a-Si: H in the LCLV makes it become a promising photoconductor. EXPERIMENTAL A-Si: H and a-SiGe: H films were deposited by RF glow discharge from the gas mixtures of 10% SiH4 in H2 and 10% GeH4 + 90N SiH4 diluted by additional 90% H2 in load-lock PCVD deposition system. The deposition process parameters were: pressure, 0.6- 2.0 torr; flow-rate, 10 sccm; substrate temperature, 200- 320"C; rf power. 5W. The composition quality of the deposited film was determined and controled from the measured IR transmittance data by an FTIR Spectrometer (5DX, Neclet). The optical energy gaps of the films. Eg(opt), were obtained by [a hv ]I/2- hv plots from the Visible-Ultraviolet Spectroscopy measurement ( UV-240, Shimadzu) . The photoconductivity was measured under AM-1 simulation at 100 mW/cm 2 . The capacitance of the film was measured at the frequency region of 0-105 Hz with an Au Schottky barrier on the film, by which we found that the capacitance of the photoconductor was not influenced by the surface barrier at the frequency above 1
Data Loading...
