The Effect Of Hydrogen On Deposition Rate, Thin Film Structure And Properties Of Silicon Based Films By Pecvd

As an important kind of optoelectronic function materials, Silicon based films have very important practical values in the high technology fields of new energy, information display and photo sensor because of its unique properties. Nowadays, hydrogenated amorphous silicon (a-Si:H) has already extensively been used in the fields of solar cells, liquid crystal display et al. However, because it contents lots of defect states (mainly dangling bonds), its application in practice has been confined in some ways. The main problem is the light-induced degradation (Staebler Wronski Effect). After a great deal of research work, scientistes all over the world have realized that hydrogen plays an important role in the structures and properties of Silicon based films. On the one hand, hydrogen incorporated as the form of monohydride (Si-H) can saturate dangling bonds in thin films. This reduces the defects state density of amorphous silicon enormously after been hydrogenated. As a result, it can satisfy the demand of device level materials. On the other hand, hydrogen incorporated as the form of polyhydride (Si-H2, Si-H3, (Si-H2)n,) can introduce new defects in thin films to increase the density of defects state of amorphous silicon. In the process of Silicon based films preparation, hydrogen has crucial effect on crystallization. On the contrary, crystallization affects the photoelectric properties of thin films. Therefore, it's very important to study the effect of hydrogen on Silicon based films.In this thesis, photoelectric properties of Silicon based films by PECVD have been studied. The research work contains four parts. First, Silicon based films of different structures and properties have been prepared by choosing different substrates and designing different process conditions. Secondary, hydrogen content and its integrating forms have been analyzed by the means of Fourier Transform infrared spectra (FTIR). Thirdly, optical properties of Silicon based films have been studied by the means of ultraviolet-visible (U-V) transmission spectra. Fourthly, electrical performances of Silicon based films have been studied by the means of electrometer. In the thesis, research work focus on the effect of hydrogen dilution ratio on growth rate of thin films, hydrogen content and the bonding forms of hydrogen-silicon. Research work also focuses on the effect of hydrogen content and of the hydrogen-silicon bonding forms on the photoelectric properties of thin films. At the same time, the effect of impurities of sodium, magnesium and calcium on the electric properties of Silicon based films have been discussed. Experimental results indicate that as the hydrogen dilution ratio, the growth rate of Silicon based films and the dark conductivity at room temperature will decrease, but the hydrogen content of thin films and the activation energy will increase and the photosensitiveness becomes better. When the hydrogen content of monohydride (Si-H) increased, the optical band gap would decrease. The hydrogen especially the hydrogen of monohydride (Si-H) will help to enhance the photoelectric properties of Silicon based films. Impurities such as sodium, magnesium and calcium can damage the photosensitiveness, decrease the activation energy and increase the dark conductivity at room temperature.