AbstractHall experiments on a series of microcrystalline, microcrystalline-amorphous, amorphous and crystalline silicon samples with varying defect densities are presented and discussed. Normal Hall effect signatures on boron and phosphorus doped hydrogenated amorphous silicon are detected. We interpret these results to be due to a small volume fraction of nanocrystalline Si, which falls below the detection limits of Raman experiments. Hydrogenated amorphous silicon, prepared under conditions far away from microcrystalline growth, shows the known double sign anomaly, Sign reversals in c-Si, where the disorder is increased by Si implantation up to very high levels, could not be detected.
AbstractWe used polarized attenuated total reflection (ATR) measurements together with Fourier transform infrared (FTIR) spectroscopy to investigate the vibrational spectra of hydrogenated amorphous silicon (a-SiHx) films 0.5-1.0 microns in thickness. We deposited the films using hot-wire or plasma-enhanced chemical vapor deposition methods (HWCVD or PECVD, respectively) on crystalline silicon and cadmium telluride substrates. Our ATR technique gave a spectral range from 2100-400 cm-1, although the Si-H wagging mode absorption band at 640 cm-1 was somewhat distorted in the a-SiHx/Si samples by impurity and lattice absorption in the silicon ATR substrates. We report the identification of a Si-O-C impurity band with maximum intensity at 1240-1230 cm-1. The assignment of this band to a Si-O-C vibration is supported by secondary-ion mass spectrometry (SIMS) measurements. Our polarized FTIR-ATR spectra of HWCVD and PECVD a-SiHx films on <111> Si ATR substrates show that the impurity dipoles are oriented strongly parallel to the film growth direction. The wagging mode absorbance band is more intense in the film plane. This trend is less pronounced for the Si-H stretching vibrations. These observations are consistent with some degree of anisotropy or medium-range order in the films. The anisotropy in the Si-H bands may be related to residual stress in the films. Our scanning electron microscopy (SEM) analyses of the samples offer additional evidence of bulk structural anisotropy in the a-SiHx/Si films. However, the Si-O-C impurity band was not observed in the polarized ATR-FTIR spectra of the a-SiHx/CdTe samples, thus indicating that the Si substrates influence formation of the impurity in the a-SiHx/Si films.
ABSTRACTHydrogenated amorphous silicon-carbon alloys, a-Si:C:H, have been deposited as thin films (d=0.1-0.5 micron) on crystalline silicon substrates from a capacitively coupled rf discharge in silane-propane mixtures. Variations in the stoichiometry of the films were achieved by altering the ratio of SiH4 to C3H8 flow rates at a sbstrate temperature in the range 240-260°C and total pressure between 30-70 mtorr. The silicon to carbon ratios were established by X-ray photoelectron spectroscopy, XPS, and the hydrogen content and distribution by infra-red spectroscopy.
High quality crystalline silicon surface passivation by combined intrinsic and n-type hydrogenated amorphous silicon