Showing papers by "Joydeep Dutta published in 1989"

Comparison of the properties of hydrogenated microcrystalline silicon films deposited by photo–chemical‐vapor deposition and glow‐discharge deposition processes

Abstract: Hydrogenated microcrystalline silicon (μc‐Si:H) films were prepared by mercury‐sensitized photo–chemical‐vapor deposition (photo‐CVD) and glow‐discharge (GD) processes from a mixture of silane and hydrogen. The variation of the growth rate, crystallinity, conductivity, and absorption coefficient with the substrate temperature, chamber pressure, and power density were studied. Highly conducting films having dark conductivity (σD)∼1×10−3 S cm−1 and ∼8.7×10−3 S cm−1 were obtained by the photo‐CVD and GD deposition processes, respectively. The merits of the photo‐CVD method over the GD process for the deposition of μc‐Si:H films for solar‐cell application are highlighted.

Radiofrequency-plasma-deposited hydrogenated fluorinated silicon-carbon alloy films

Abstract: Properties of ${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{C}}_{\mathrm{x}}$:F:H films prepared from silicon tetrafluoride\char21{}carbon tetrafluoride\char21{}hydrogen gas mixtures by radiofrequency-plasma-enhanced chemical-vapor deposition are reported. The dark conductivity and its activation energy are found to be very sensitive to the proportion of hydrogen. The infrared absorption spectra suggest a microcrystalline structure in films prepared at low hydrogen dilution. This has been confirmed by the transmission electron microscopy. At larger hydrogen dilution, photosensitive, amorphous material is formed. The constant photocurrent spectra and space-charge-limited current studies combine to reveal a low density of shallow as well as deep defects. The photoconductivities of these films are found to be superior to those prepared without fluorine for band gaps larger than 1.85 eV. The material properties may be understood in terms of the relative concentrations of ionic and atomic hydrogen and fluorine in the plasma and at the growth surface.

Effect of ultraviolet irradiation on the white light degraded electronic properties of hydrogenated amorphous silicon films

Abstract: The electronic properties of hydrogenated amorphous silicon (a‐Si:H) thin films are known to undergo metastable light‐induced changes that can be reversed by annealing at elevated temperatures. We have observed for the first time that annealing of the light‐induced changes in the dark conductivity and photoconductivity of a‐Si:H thin films can also be achieved by ultraviolet (UV) irradiation (wavelength ∼254 nm) of the films at room temperature. It has been shown that the bulk photoconductivity changes in spite of the fact that UV radiation is mostly absorbed near the top surface of the films. A simple explanation of the observed phenomena has been proposed involving a nonequilibrium distribution of phonons generated by absorption of high‐energy photons in the material.