The Research On The Properties Of Hydrogenation Amorphous/nanocrystalline Silicon Thin Films Prepared By PECVD

Compared with monocrystalline silicon, a-Si:H/nc-Si:H not only have high light absorption coefficient, but also have many other properties like adjustable optical band gap, electrical conductivity and low cost. They have been more and more used in the fields such as optical modulator, optical sensors, solar cells and thin film transistor and so on.The film-forming and doping mechanism of a-Si:H/nc-Si:H are complicated. A large number of experimental studies show that films’ microstructure and performance are highly affected by the preparation conditions. The academic research on these subject are still not very full, especially on heavily phosphorus and lightly boron doping in our country.The work in this paper was done to study the above problem. Intrinsic and doped a-Si:H was prepared by using RF-PECVD technique. Annealing experiment was done on intrinsic a-Si:H. The properties of films were studied systematically by using a variety of analysis methods. A complete liquid crystal spatial light modulator device with a boron doped hydrogenated amorphous silicon photosensitive layer was prepared in this paper. The main research contents and achievements include the following aspects:(1) Annealing experiments show that obvious crystallization phenomenon appear in the films when the temperature reached 900℃; The films annealed at 500 and 700 were all amorphous, and there crystal structure were complex; The film of annealing temperature of 700℃ emerges a large number of pinholes. The optical band gap and conductivity of the crystallized films were increased significantly.(2) Hydrogen has a certain role in promoting the crystallization of thin films using the hydrogen dilution and layer by layer with the preparation of hydrogenated silicon thin film. But high density hydrogen plasma etching will bring serious and a large number of voids defects on the film surface, which finally easily mark films serious oxy-genated.(3) Phosphorus doped silicon thin films were amorphous, and the structure factor R* were larger; Optical band gap of films had widened by Phosphorus incorporation, which reach to the maximum in 2.5% of the phosphine concentration. The conductivity of phosphorus doped a-Si:H films is about 5 orders of magnitude higher than undoped films, but photo-conductivity and dark-conductivity is almost no difference, the high concentration of the phosphorus doped lead to decreasing of the electric conductivity.(4) The right amount of boron doped can promote hydrogenated amorphous silicon to achieve "The eigenstate of electricity". Trace boron doping will affect optical properties and microstructure of the film; Boron doped a-Si:H thin film of certain parameters is applied to the photosensitive layer of the liquid crystal spatial light modulator, which has achieved good imaging effect.