Controlling On Defect Of Hydrogenated Nanocrystalline Silicon Thin Films

People are consuming more and more energy with the rapid development of science and technology. Over the past decade of this 21 st century, the process of industrialization is making the shortage of traditional energy and deterioration of environment become the major global crises threatening survival and development of human being.Therefore, exploitation of clean and renewable energy resources becomes the main focus of our society. As an equipment with the advancement of converting the inexhaustible and green energy of sunlight to electricity,solar cells are attracting more and more attention. The problem of the current crystalline silicon solar cells lies in its high-energy consuming and pollution of the environment during the producing process. The novel thin film solar cells have attracted great attention due to their advantages including simplified preparation method, low manufacturing cost, and low consuming of material as well as energy. As the main material of the new generation thin film solar cells, hydrogenated nanocrystalline silicon(nc-Si:H) shows great promise due to good features such as a tunablebandgap, strong optical absorption, high carrier mobility, and good stability against light soaking.This mixed-phase material consists of nanometer grains embedded in an amorphous matrix, which on the other hand determines that defect structures such as grain boundaries and nanometer-sized voids also exist in the films. There are a lot of unsaturated silicon dangling bonds in these areas, which are the source of defect density of this material. On the other hand, these defect struture can afford incorporation location for the oxygen impurities out of post-deposition oxidation. These oxygen impurities can further form the Si-O/Si defect in the films. Therefore, the controlling of the defect density as well as the oxygen impurities becomes the main focusing point for this material.A series of samples were deposited under different H dilution profiling, and these samples were characterized by Raman, x-ray diffraction, transmission electron microscope and optical transmission measurements. Based on further analysis on the information from the infrared absorption spectrum, we gave a dicussion on the influence of the hydrogen’s behavier on the evolution of the samples’ structure and the mechanism of the way oxygen impurities incorperate in the materials.Moreover, we made another series of nc-Si:H samples by applying an extra substrate bias on the plasma enhanced chemical vapor deposition system. The results of electron spin-resonance spectroscopy and minoritycarrier lifetime measurement gave us the conclusion that the bias has an effective passivating effect on the samples, and can improve the theie density as well. Based on the analysis of infrared absorption spectrum results, we made a detailed discussion on the mechanism of the substrate bias’ passivating effect on the materials. Finally, we deposited a series of P doped nc-Si:H samples by applying substrate bias, and based on the measurements of infrared absorption spectrum, secondary ion mass spectroscopy as well as x-ray photoelectron spectroscopy we can conclude that the applied substrate bias can effectively improve the dopping efficiency of the p doped nc-Si:H thin films.All the works in this dissertation were supported by National Major Basic Research Project(2012CB934302), and Natural Science Foundation of China(11174202 and 61234005).