Microstructure and Optical Properties of Amorphous/Nanocrystalline Silicon Films
|Keywords||nc-Si optical band gap bonding configurations multilayer|
Amorphous and nanocrystalline silicon thin films had been deposited by HWP-CVD technique on single crystal silicon and corning glass substrates from SiH4 and H2 reactants. A variety of techniques, such as fourier transform infrared spectroscopy, ultraviolet-visible transmittance and reflection spectroscopy, atomic force microscopy are utilized to analyze the crystalline fraction, bonding configurations, surface morphology and optical gap of the deposited films. The effects of the experiment parameters such as hydrogen flow rates and film thickness on the structural and optical characteristics of the deposited films were studied. A multilayer nc-Si film was designed according to the preparation conditions for amorphous and nanocrystalline silicon. Furthermore, the relation between the microstructure and optical property were investigated as well.Nc-Si thin films were deposited through modulating the H2 reactant. Hydrogenated amorphous silicon films were deposited at the lower H2 reactant, while hydrogenated nanocrystalline silicon films were obtained at the higher H2 reactant. It has been shown that the optical band gap Eg and the disorder of the films were increased, but the hydrogen contents CH were decreased with increasing H2 flow rates.A varity of a-Si/nc-Si heterojunction thin films with different nc-Si thickness has been deposited by the HWP-CVD technique, in which a-Si:H films as the accubation layer. It had been shown that the optical band gap Eg and the disorder of the films were increased with increasing the thickness of the films. As the bulk layer increases small nanocrystals were nucleated. A multilayer structure has been designed in which the nanocrystallites Si layers are interbedded periodically in amorphous Si layer. It was shown that the multilayer films were in amorphous structrure. The microstructure order of the multilayer films could be well improved, while the optical band gap Eg was decreased with increasing the thickness of nanocrystallites Si layer.