Studies On Properties And Mechanism Of Silicon-Based Films Deposited By CVD

Featured by wide band gap, high breakage electric field, high electron mobility, low dielectric constant, strong irradiation proof and excellent chemical stability, silicon carbide (SiC), viewed as one of the most promising wide band gap semiconductors, is widely utilized in optoelectronic devices, high frequency and large power, high temperature electronic devices. Hydrogenated amorphous silicon (a-Si:H) by virtue of its superior properties is increasingly playing an important role in the high-technology field, such as film solar cells, film transistor and flat display.In this study, β-SiC film was acquired, only with the aid of the catalyst's thermal radiation, utilizing self designed Cat-CVD system at an actual temperature below 300?C of the substrate unheated. Hence, not only did this progress extend new synthesis techniques, but also promoted low temperature CVD synthesis of β-SiC film to a new stage. Moreover, high quality nanocrystalline β-SiC film was attained with the integration of the pre-carbonization process and the substrate bias effect.In order to deposit device quality a-Si:H films, various preparation methods have been thoroughly studied. In view of its virtue of high degree of electron and ion generations, the microwave electron cyclotron resonance (MWECR) CVD method is expected to deposit device quality a-Si:H at high deposition rate. Thus, we have prepared a-Si:H films under diverse conditions using MWECR CVD. Moreover, we are concerned with hydrogen content in films and discuss its effect on photoelectricity of films.The dissertation mainly focuses on variation of the structure of a-Si:H as functions of the dilution ratio of H2/SiH4, substrate temperature and substrate position at low microwave power. We experimented by varying the dilution ratio of H2/SiH4 at different substrate position, and found that the optimum dilution ratio of H2/SiH4 ofsystem depends on substrate position. At the same time, we experimented by varying substrate temperature, and found that high substrate temperature is favorable to hydrogen elimination and thus improve the structure of films, but over high substrate temperature leads to the increase of dangling bonds.Hydrogen incorporated as monohydride (Si-H) saturates dangling bonds in films, and on the other hand, hydrogen incorporated as polyhydride (Si-H2,Si-H3, (Si-H2)n) introduces defect in films and thus increases the density of localized electronic states in band gap. We obtained hydrogen content and bonding configurations of films by analyzing the integrated absorbance of the wagging mode and stretching mode. We found that hydrogen content incorporated as monohydride maintains constant and hydrogen content incorporated as polyhydride gradually decreases with the increase of substrate temperature. At the same time, we also found optical band gap decreases and photosensitivity of a-Si:H films increases with the increase of substrate temperature. So, the decrease of optical band gap is the result of the decrease of hydrogen content, especially incorporated as polydride.