Study And Preparation Of The Hydrogenated Amorphous Silicon Liquid Crystal Spatial Light Modulator

The liquid crystal spatial light modulator is a kind device which can modulate the light in optical field distribution. It can receive electrical signals or light signals and modulate the amplitude, phase, intensity of another kind optical signal. This device was widely used in spatial filtering, image processing, large-screen display and so on, which greatly facilitates the exchange and transmission of visual information.Therefore,the study of the nature of the function layers to improve the resolution and response speed is very necessary.This dissertation analyzed the principles of the liquid crystal spatial light modulator, and presented the requirements of function layers theoretically. The light and dark conductivity ratio of the photosensitive layer directly determines the performance of the device. The hydrogenated amorphous silicon was used as photosensitive layer in this dissertation. By adjusting different deposition parameters and using a variety of analytical test methods, this dissertation studied the gas temperature, RF power density, gas flow rate, deposition pressure and different doping ratio of the films to the influence on electro-optical properties of hydrogenated amorphous silicon films. Then according to the test results, we optimized the deposition parameters, prepared the photosensitive layer which is good in quality.Boron-doped a-Si:H thin film was fabricated by the Plasma Enhanced Chemical Vapor Deposition(PECVD) method on ITO glass, with high purity silane(SiH4) as the reaction gas and borane(B2H6) as the dopant. The influence of boron-doping amount on conductivity, refractive index, and extinction coefficient and band gap were measured. The results show that with the increasing concentration of boron doping amount, the dark conductivity of the films decreases and increases later on. The extinction coefficient and band gap increases and then decreases as the increasing boron doping amount. Without changing the experimental process conditions, we determined the optimum doing ratio (the maximum ration of the bright and dark conductivity) of the films, and fabricated the lightly doped hydrogenated amorphous silicon thin film which is suitable for the use of device-level photosensitive layer. Also, the absorbing layer and dielectric mirror was prepared.The light absorbing layer in the spatial light modulator mainly absorbed the remaining light to prevent light from entering the photosensitive layer. In this experiment, CdTe films were prepared by thermal evaporation. The UV-visible optical meter was used to test the transmittance of the films. On this basis, the transmittance of the hydrogenated amorphous silicon films and CdTe films was tested. Dielectric mirror in the device isolated the written light and reading light. Tests show that in central wavelength of 540 nm the reflectance of the dielectric mirror films can reach as much as 99.8%.In the preparation of the liquid crystal cell, first we discussed the working principle of the TN cell, then the problems we met and corresponding methods was discussed and tested the performance of the liquid crystal spatial light modulator. The test results show that the modulator prepared in this dissertation meet the basic requirements and achieve the goal of wavelength conversion.