Deposition And Properties Of Hydrogenated Polycrystalline Silicon Films By HWCVD And RF-PECVD Composite Technology

The increasing in energy consumption causes a severe shortage of traditional energies. In the case of global energy crisis, the development of new energy has been taken top of the agenda by many countries in the world. Solar cells made from semiconductor materials can transform luminous into electric energy. Silicon is one of the important semiconductors with non-toxicity. harmlessness and abundant. Silicon photovoltaic materials possess great potential in photovoltaic devices (solar cells) and thin film transistors (TFTs).It is uncomplicated to deposit hydrogenated amorphous silicon (a-Si:H) on large area substrates with good photosensitivity via radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD). During the deposition process, however, the growth films will be bombarded by high-energy ions in the plasmas, which can result in hindering the crystallization of the films. On the other hand, the hot-wire chemical vapor deposition (HWCVD) method for the preparation of μc-Si films has attracted considerable attention because of the simple setup and the possibilities of high deposition rate. A large number of hydrogen atoms prompt structural relaxation and then crystallization of the deposited films due to the complete decomposition of reactant mixtures by high temperature hot wire. Nevertheless, too fast growth rate will result in incompact and the films are prone to be oxidized in the air. A combination deposition technique of HWCVD with RF inductively coupled plasma (ICP) should be able to overcome their respective disadvantages. In this article, μc-Si films were deposited by the composite technique of HWCVD and ICP on the glass slides or the ploymide substrates. The microstructure, growth rate and optical properties of the films were investigated.The deposition parameters, including the distance between the hot wire and the substrate, the power of radio frequency and the flow rate of the hydrogen, were changed to prepare a series of silicon films. The effects of these deposition parameters on the crystallization rate, the crystalline structure, the energy gaps, the bonding structure of the silicon films were systematically investigated by Raman Spectroscopy, X-ray diffraction analysis(XRD), UV-visible spectrometer, and FT-IR spectra, respectively. The results demonstrate that the crystalline volume fraction increases, the energy gap decreases and the preferred orientation changes from (111) to (220) with the decrease of the distance between the hot wire and substrate. The introduction of RF-PECVD is helpful for the growth of lattice plane (220). The increase of RF power contributes to the crystallization of the films, but the crystallization of the films decrease and the roughness increase when the RF power is above200W. As the hydrogen content increasing, the crystallization of the films increases, hydrogen content in the bonding states reduces, the defects of the film also reduce but the band gap first increases and the decreases.