Deposition And Optical Properties Of Doped Nano-silicon Carbide Thin Films

Nanocrystalline 3C silicon carbide (3C-SiC) and nanocrystalline 6H-SiC thin films doped with nitrogen have been deposited by helicon wave plasma enhanced chemical vapor deposition (HWP-CVD) on single crystalline silicon wafer and Corning 7059 glass substrates. A variety of techniques, including Fourier transform infrared spectroscopy, X-ray diffraction, ultraviolet-visible transmittance and reflection spectroscopy, scan electron microscopy, atomic force microscopy, X-ray energy electron spectroscopy, photoluminescence (PL) spectra and photoluminescence excitation (PLE) spectra are utilized to analyze the crystalline fraction, bonding configurations, morphology, optical gap, the PL property and luminescence mechanism of the films. The effects of the nitrogen doping on the structural and optical characteristics of the films are studied respectively. Furthermore, it is also investigated for the hydrogen flow rates affecting the structural and optical characteristics of the N-doped 6H-SiC films. the primary results are included as follows.Nanocrystalline 3C-SiC thin films can be deposited by the HWP-CVD at a relatively low substrate temperature. At lower N doping, the doping mechanism is C being substituted by nitrogen. With increasing the N doping, the size of nanocrystalline SiC grains decreases, while a reverse trend is obtained for the concentration of Si-N bond, which make the bandgap of the films become widen. The PL analysis shows that nitrogen incorporating in the film will result in the increase of Si defect density, the PL of N doped nanocrystalline 3C-SiC thin films mainly origin from the quantum confinement effect and Si defect luminescent centers. At moderate N doping, The bandgap of films is narrowed with increasing the density of the impurity state and the luminescence mainly related with the radiate carrier recombination between impurity state and value band. At higher N doping, the decrease of the Nanocrystalline SiC grains and increase of Si-N bonds result in wider band gap. The PL is interpreted by the model of interface state defect luminescence.Nanocrystalline 6H-SiC film with high crystalline volume fraction can been deposited at higher substrate temperature. The deposition rate increases and their crystallization degree decreases with the increase of N doping. The growth terminating effect of N impurity cause the nanocrystalline size reduced and the Eu energy of the films decreased. The optical band gap increase initially and then decrease, which is determined by the increase of quantum size effect of nanocrystalline SiC and that of N impurity density of states. At the same time, the wavelength photoluminescence is blueshifted and their full width half maximum becomes narrowed.At fixed N doping content, the etch effect of the active hydrogen enhance the deposition rate and N content in the films decrease, the crystallinity and the size of the nanocrystalline SiC increase with H2 flow rate increasing. The analysis of optical absorption properties indicates that the optical gap of thin films decreases and the microstructure order degree enhanced.