R. Thangaraj

The preparation, properties and applications of silicon nitride thin films deposited by plasma-enhanced chemical vapor deposition

Abstract The purpose of this paper is to review the preparation and characterization of thin films of silicon nitride deposited by the technique of plasma-enhanced chemical vapor deposition. The applications of silicon nitride thin films in integrated circuit technology are also reviewed. The paper also introduces the modifications to the plasma chemical vapor deposition system used to avoid plasma bombardment of the substrate and to reduce hydrogen incorporation in the layers in the form of Si-H and N-H bonds. The effect on film properties of post-deposition annealing at a temperature higher than the deposition temperature is reported.

Structural and optical properties of sprayed CuInS2 films

Abstract CuInS2 thin films were prepared by spray pyrolysis. The films were characterized by X-ray diffraction, transmission and scanning electron microscopy, optical transmission and electrical measurements. They were found to exhibit p-type conductivity with a preferred orientation of (112) parallel to the substrate.

Totally sprayed CuInSe2/Cd(Zn)S and CuInS2/Cd(Zn)S solar cells

Abstract Low resistivity (0.1 – 1 Ω cm) p-type CuInSe2 and CuInS2 thin films were prepared by pyrolytic decomposition. The films had a predominantly chalcopyrite structure with a (112) orientation suitable for CdS/CuInX2 solar cells. X-ray photoelectron spectroscopy studies showed that the CuInSe2 films were free from binaries such as Cu2Se, In2O3 and In2Se3. Thin film solar cells of CuInSe2/Cd(Zn)S and CuInS2/Cd(Zn)S with efficiencies of about 3% and 2.6% respectively were fabricated.

Structural and optical properties of sprayed CuInSe2 films

p-CuInSe2 thin films with the chalcopyrite structure were prepared by spray pyrolysis. The films were characterized by X-ray diffraction, optical transmission, transmission and scanning electron microscopy and electrical measurements. They were found to have a preferred orientation with (112) parallel to the substrate. The resistivity of these films was varied from 0.1 to about 100 ω cm by varying the Cu:In ratio from 1.2 to unity.

Structural, optical and photoconducting properties of sprayed CdSe films

Abstract CdSe films were grown by the pyrolytic decomposition of a mixture of aqueous solutions of selenourea (NH 2 CSeNH 2 ) and CdCl 2 ·5H 2 O. The effect of changes in the selenium-to-cadmium ion ratio on the photoconductivity was examined. The as-grown films had low resistance and showed poor photoconductivity gain. When the films were annealed in air the resistance as well as the gain increased appreciably. These changes have been attributed to chemisorption of oxygen. The samples with one part CdCl 2 ·5H 2 O and one part NH 2 CSeNH 2 were found to be the most photosensitive, the ratio of dark resistance to light resistance being of the order of 10 5 . The spectral response of the resistance of these films shows a dip in the region of 690 nm, which is in close agreement with the band gap determined from optical absorption measurements.

Characterization of fluorine-doped SnO2 films prepared by chemical vapour deposition

Abstract Low resistance (6ω/□) and highly transparent (83%) fluorine-doped SnO2 films were prepared by chemical vapour deposition and by optimizing the substrate temperature (about 350 °C), the oxygen flow rate (about 2.51 min-1) and the fluorine doping concentration (1.02 wt.%). The direct and indirect band gaps determined from the optical data were 4.29 eV and 2.74 eV respectively. X-ray diffraction patterns and scanning electron micrographs showed that the films have good crystallinity and do not show preferred orientation. These properties make the films suitable for application as top conducting layers in semiconductor/insulator/ semiconductor solar cells.

The effect of tin additions on indium oxide selective coatings

The effects of adding up to 50 mole.% of tin to pyrolytic In2O3 selective coatings were investigated. Up to 10% doping the resistivity is found to decrease with the corresponding increase of carrier concentration. Further additions increase the resistivity and decrease the carrier concentration. X-ray diffraction and electron microscope observations indicated that (400) is the strongest peak. The tin additions cause the lattice parameter to decrease indicating that the decrease in resistivity is caused due to the replacement of In3+ ions by Sn4+ ions. The increase of resistivity at higher tin additions is due to poor crystallinity. The films with low resistivities had very low activation energies for electrical conduction.

Structural, optical and photoluminescence properties of electron beam evaporated CdSe1−xTex films

Abstract CdSe 1−x Te x (0 ⩽ x ⩽ 1) films have been prepared by electron beam evaporation using pellets made by mixing CdSe and CdTe powder in appropriate ratios. For the films prepared at 200°C substrate temperatyre, the XRD pattern of CdTe ( x = 1 ) showed the presence of free Te while films of all other compositions were single phase in nature. The effect of composition and substrate temperature on transmission spectra was studied. The photoluminescence studies showed sub-band-gap luminescence throughout the composition range. Annealed CdSe0.8Te0.2 films showed better photoluminescence efficiency as compared to as-grown films. The refractive index was found to increase with substrate temperature for CdSe0.8Te0.2 films.

Thickness dependence of the electrical and structural properties of In2O3:Sn films

Films of In2O3:Sn (10 wt.% Sn) of various thicknesses were deposited onto heated glass substrates (450 °C) by spray pyrolysis. The electrical and structural properties were studied for different thicknesses, and the scattering mechanism is discussed. Hall measurements showed that thicker films (about 500 mm) have relatively higher Hall mobilities compared with those of thinner films. The electrical resistivity of a film about 600 nm thick was found to be about 2.66 x 10-6 ωm at room temperature, and the average transmission in the visible range was found to be 86%. The high carrier concentration (6.49 × 1026 m-3) and the negligible dependence of the electrical properties on temperature show that the films are degenerate. The relationship between carrier concentration and Hall mobility revealed that the ionized impurity scattering centres were the dominant cause of scattering.

Ni-Al2O3 selective cermet coatings for photothermal conversion up to 500°C

Spectrally selective Ni-Al2O3 composite films were prepared by r.f. planar magnetron sputtering using hot-pressed targets of two different compositions. The composition of the films were varied by co-sputtering the target with additional nickel pellets distributed uniformly on the target. The composition of the films were analysed by energy-dispersive X-ray analysis. Optical simulations were carried out with the experimentally measured n and k and the published n and k of the metallic substrate. R.f.-sputtered SiO2 and Al2O3 were used as antireflection coatings. From the computer optimization studies we found that α = 0.94 and e(100°C) = 0.07 could be obtained with 650 A of Ni-Al2O3 (f = 0.61) antireflected with 780 A SiO2 on a nickel-coated glass substrate. When molybdenum-coated nickel-plated stainless steel substrates were used, the films were found to be stable up to 500°C in air.