The deposition processes and the properties of a-SiC:H and a-SiGe:H films in 55 kHz glow discharge were investigated. The analysis of deposition rate and RBS measurements showed that the chemical reactions between SiHn spices and CH4 control the incorporation of C in a-SiC:H films. High deposition rates of a-SiC:H and a-SiGe:H films fabricated by 55 kHz PECVD is caused by the increase of radical fluxes to the growth surface. The specific features of a-SiC:H and a-SiGe:H microstructure were revealed by IR and AFM analysis. In a-SiC:H films the islands of low size were distinguished on the surfaces of large islands. The large variation of the total hydrogen content in a-SiGe:H did not affect the optical bandgap, while the hydrogen related microstructure controlled the electronic properties such as dark conductivity, 11p.r product, defect density and Urbach slope.The results of optoelectronic properties and SW effect measurements of 55 kHz a-SiC:H and a-SiGe:H films demonstrated the increased stability in comparison with a-Si:H.
In this work, a-Si:H films with good electronic properties in spite of an inhomogeneous structure were prepared by the 55 kHz plasma enhanced chemical vapor high-rate deposition technique. The structural analysis using infrared spectroscopy and atomic force microscopy has shown that these films possess two dominant types of microstructural inhomogeneities, which differ by size. To analyze the influence of a 55 kHz plasma on the properties of intrinsic a-Si:H film, the density of states in the a-Si:H mobility gap was estimated by modeling of the temperature dependence of the photoconductivity and from electron paramagnetic resonance measurements. Investigated capacitance-voltage characteristics showed that a-Si:H/c-Si heterostructures have low interface density of states and can be considered as an ideal abrupt heterojunction.
In this work the mechanism of hydrogen incorporation and structural stability of a-Si:H films deposited by LF 55 kHz glow discharge in a wide range of technological parameters have been investigated. The analysis of plasma emission spectra and microstructure of films measured by IR spectroscopy and atomic force microscopy were carried out. It was shown that hydrogen desorption controls the growth rate in a wide range of substrate temperature (40–325°C ) and at low values of LF power (50–200W). At the same time the abnormal increase of hydrogen content due to ion-molecule surface reactions with the increase of substrate temperature was observed. The kinetics of hydrogen diffusion and thermodynamics of defect formation in a-SiH films were determined from modeling of differential scanning calorimetry data. It is concluded that the mechanism of hydrogen incorporation leads to formation of strong Sill bonds in the material bulk and to increase of structural stability with the increase of substrate temperature despite of the increase of hydrogen content.
The 55 kHz GD technique allowed the high-rate deposition of a-Si:H films (up to 30 A/s) with good electronic properties in spite of inhomogeneous structure. In this work, we investigated the growth mechanisms and the correlation between plasma parameters and film structure. The electrical parameters of discharge, the properties of plasma and of the films were investigated with using of wide range of methods (optical emission spectroscopy, mass-spectrometry, IR-spectroscopy, atomic force microscopy).The films were deposited in an industrial reactor of diode type with both non-grounded electrodes used as substrate holders. The deposition mechanism in this case includes the alternation of growth phases when the negatively charged particles reach the anode (at a moment) during the first half-period of an oscillation of electric field, and the improvement of growing surface under the influence of the bombardment by positive ions during the second half-period. It is shown that the increase of the power increases the ionic flux leading to the increase of the size of structural inhomogeneities. The pressure influences the energy of positive ions, and, therefore, the hydrogen content and its bonding form on the growing surface.
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