Fabrication And Optoelectronic Properties Of High Quality Hydrogenated Amorphous SiC Thin Fihns And Nanocrystalline Si/SiC Structures

It becomes a popular issue to develop the clean energy such as solar energy for the purpose of solving the energy-short problem. High performance semiconductor solar cell materials especially for the silicon-based materials have important significance in both fundamental research and application interesting, which have attracted much attention in the worldwide range.In this thesis, hydrogenated amorphous silicon carbon thin films (a-SiC:H) were prepared in conventional plasma enhanced chemical vapor deposition system with various gas ratio R=[CH4]/[SiH4] and their microstructures, optical and carrier transport properties were investigated. Furthermore, we applied layer-by-layer hydrogen plasma treatment technique to obtain the high quality silicon carbon thin films with high photosensitivity. On the other hand, the nc-Si embedded in amorphous SiC network and nc-Si/SiC multilayer films were fabricated by post annealing treatment and the change of the microstructures and optical, electrical properties of the according films were studied. Finally, we tried to prepare the novel solar cell device structures based on the nc-Si/SiC multilayers and observed the photovoltaic properties.The main content and the results of this thesis are listed as following:1. A series of Si-rich amorphous silicon carbide (a-SiC:H) thin films were deposited in conventional plasma enhanced chemical vapor deposition system with various gas ratio R=[CH4]/[SiH4]. The microstructural, optical and electronic properties of as-deposited films were investigated. It was demonstrated that the optical band gap is linearly proportional to the carbon content in the films and it can be controlled in a range of1.8-2.4eV by changing the gas ratio R. Moreover, the absorption of the samples is decreased with the carbon content increasing. Both the room-temperature dark and photo conductivities were decreased with increasing the carbon content in the films and the photosensitivity reaches as high as103for the film with the optical band gap of2.0eV.2. Hydrogenated amorphous silicon carbide thin films (a-SiC:H) were fabricated using the layer-by-layer hydrogenated treatment technique by controlling the hydrogen plasma annealing-time. The changes of microstructures and compositions were characterized by Raman、FTIR and XPS spectra. It is found that the photo-conductivity for the hydrogenated samples was improved obviously after hydrogen plasma annealing, which can be attributed to the formation of dense and ordered films due to hydrogen annealing as well as hydrogen passivation effect, The photo-sensitivity can be reached to a high value of106for the prepared hydrogenated silicon carbon thin films.3. Nanocrystalline Si (nc-Si) embedded in amorphous SiC host matrix was obtained after annealing the single layer amorphous SiC films. Room temperature electroluminescence located at about650nm can be observed. It is demonstrated that the intensity of the electroluminescence was improved with increasing the injection current. Moreover, nc-Si/SiC multilayers were further fabricated by annealing a-Si/SiC stacked structures and the change of the microstructures was characterized by the TEM and Raman spectra. It is found that the nano-Si Quantum Dots were formed after annealing, and the absorption peak was red-shift with the increasing of the thickness of the silicon layer, which was consistent with the Quantum Confined Effect. Moreover, we also design the novel solar cell device based on nc-Si/SiC multilayers and graded-size multilayered structures, which has the photo-electric conversion efficiency of6.18%.