Liu Xiangna

Cubic Silicon Carbite Film Growth and Characterization by Hot Filament Chemical Vapor Deposition

Cubic silicon carbide films (β-SiC) have been successfully grown on monocrystalline silicon wafers by hot filament chemical vapor deposition (HFCVD) at temperatures ranging from 500 to 650°C, fulfilled by a two step process. Raman spectrum of the HFCVD-grown β-SiC films shows a characteristic peak at 975 cm-1 with a full width at half maximum (FWHM) of 76 cm-1. At room temperature, the films emit visible photoluminescence at 580 nm with an FWHM of 0.4 eV. X-ray diffraction and x-ray photoelectron spectroscopy investigations reveal that the epitaxial films are of good quality.

Photoabsorption Spectra of Nano-Crystalline Silicon Films

The photoabsorption spectra of nano-crystalline silicon (nc-Si:H) films were measured by means of constant photoconductivity method. We investigated the changes of absorption spectra with the increasing of crystallinity as the deposited films are amorphous, microcrystalline and nano-crystalline. We found that in nc-Si:H the transition processes in the interfacial region between the grains predominate the whole range of the absorption spectra. We related the phenomenon to the structural changes in the material.

Investigation of nitrogen content influence on electron spin resonance in a-Si:H/a-SiNx:H mulatlatyers

Influence of nitrogen content on electron spin resonance (ESR) in a-Si:H/a-SiNx:H multilayers is studied, associated with infrared absorption analysis. The spin density decreases rapidly in the region x 0.7 and approaches a saturated value, which is much less than common assumption. The results are explained in terms of the structure relaxation due to the increase of N-H bonds with increasing x and the transfer doping across interfaces.

The Staebler-Wronski effect in microcrystalline silicon films

Light-induced dark- and photoconductivity changes (so-called SWE) have been investigated on GD undoped microcrystalline Si:H(μc-Si:H). The SWE decreases and reaches vanishing as the grain size increases. An interpretation for the two-phase structure and the contribution of grain boundary defects is given.

Photoluminescence properties of nano-size crystalline silicon films

Photoluminescence (PL) at low temperature is reported for nc-Si:H films grown by PECVD. A characteristic luminescence peak was observed in the wavelength range of 1.1-1.2 μm. The temperature dependence of PL has been studied in the temperature range of 4.2-180 K. The PL mechanism of nc-Si:H films is discussed. The emission peak at 1.1-1.2 μm is attributed to the interface atoms between grains, and the emission peak around 0.9 μm is due to a little amount of amorphous component.

Deposition of high quality amorphous silicon films with strong hydrogen diluted silane as reactant gas source

By using strongly hydrogen diluted silane as a reactant gas source [C(=SiH4/(SiH4+H2))<5%] in a conventional diode PECVD system, we have deposited high quality a-Si:H films which exhibit almost no Steable-Wronski (S-W) effect. The [H] radical in rf plasma erodes the growing surface and eliminates the weak Si-Si bonds, thus reducing the density of metastable defects of a-Si:H films and causing the amorphous network to be more perfect. Our results show that as C value decreases from 5.4% to 0.8%, the peak location of TO mode in Raman spectra changes from 480 to 500 cm-1, the average distortion of bond angles Δθ, which is calculated from the width of half full height of TO peaks, reduces from 9.0° to 3.8°. The hydrogen content CH of the samples which show almost no S-W effect is less than 10 at%.

Interfacial Properties of a-Si:H/a-SiNx:H Multilayers Studied by electroabsorption Spectroscopy

By using electroabsorption method, we find that the built-in field (similar 105 V?cm-1) in the a-Si sublayers of a-Si:H/a-SiNx:H multilayers points towards the sample surfaces. We ascribe the internal field to the asymmetric distribution of defect states which exist primarily in the silicon side of the silicon-on-nitride interfaces, owing to the large repellent lattice stress there. We also find that the built-in potential depends strongly on x, with a maximum value near x = 1.0. We intend to explain it as a result of structural softening as more N atoms are introduced into Si networks in the range of x > 1.0.