Characterization of Undoped, N- and P-Type Hydrogenated Nanocrystalline Silicon Carbide Films Deposited by Hot-Wire Chemical Vapor Deposition at Low Temperatures

摘要

Undoped, n- and p-type hydrogenated nanocrystalline cubic silicon carbide (nc-3C-SiC:H) films were successfully deposited on glass and silicon substrates at a low substrate temperature of about 300℃ by hot-wire chemical vapor deposition. The structural, optical, and electrical properties of the films were investigated by X-ray diffraction (XRD), Fourier transform infrared absorption (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry, photothermal deflection spectroscopy (PDS), and conductivity measurements. The XRD and FTIR measurements revealed a clear correlation between the average grain size and width of the SiC stretching mode vibration of the films. The dark conductivity of the films was increased from 5.8 x 10~(-11) to 6.2 x 10~(-6) S/cm with increasing the grain size from 6.4 to 16.6 nm. The detailed analysis of the dark conductivity indicates that the Fermi level position is affected by the grain size of the films. Spectroscopic ellipsometry measurements showed that the dielectric functions of the films are strongly affected by the grain size. The n- and p-type nc-3C-SiC:H films were also successfully deposited using phosphine, hexamethyldisilazane, and dimethylaluminumhydride as dopants. For the n- and p-type films, the dark conductivities of 5.32 x 10~(-0) and 7.67 x 10~(-4) S/cm were achieved, respectively. The optical absorption spectra of the doped films indicate that p-type doping significantly affects absorption coefficients above the bandgap of nc-3C-SiC:H compared with n-type doping. For the n-type films, the absorption coefficients below the bandgap are affected by free carrier absorption as well as by localized states within the bandgap.