Electrosynthesis and photoelectroactivity of polycrystallinep-zinc selenide

The photoelectroactivity of polycrystalline zinc selenide films prepared by electrochemical codeposition in zinc sulphate solutions of different concentrations containing theI ⁻/I ₂ redox couple has been investigated. Measured photopotentials, photocurrents and the initial rate of build-up of photopotentials indicate a significant enhancement in photoelectro-convertibility with increase in concentration, in spite of practically no change in the flat band potentials. The photoelectroactivity of ap-n heterojunction photoelectrochemical cell using cadmium selenide along with zinc selenide has also been studied.     

The structure and semiconducting properties of cadmium selenide films

CdSe films about 1 μm thick were vacuum deposited on unheated glass substrates. Reflection electron diffraction studies showed the growth of a one-dimensional {00.1} texture orientation of the hexagonal phase. Films of lower resistivity were characterized by a larger grain size and better ordering, whilst films of higher resistivity contained amorphous regions and were less ordered. A study of the carrier type, the concentration, the Hall mobility and the variation in the bond length u along the hexagonal c axis of “as-deposited” and heat-treated films showed that the lower resistivity films incorporated a small cadmium excess, which increased with heat treatment, resulting in higher carrier concentrations and a further lowering of the resistivity. Large increases in the resistivities of films deposited at high rates were attributed to the depletion of the small individual grains.     

Space-charge-limited conductivity in evaporated cadmium selenide thin films

We have studied the basic d.c. electrical properties of evaporated CdSe films in the context of the development of inexpensive solar cells. Earlier measurements have shown significant variations, which depend on the preparation and previous treatment of the films. In the present work Al---CdSe---Al sandwich structures were studied, with the CdSe thickness in the range 0.1–1.0 (μm. D.c. capacitance varied inversely with film thickness, yielding a permittivity of 7.82 × 10⁻¹¹ F m⁻¹ (relative permittivity 8.83). Current density was proportional to applied voltage at low voltage levels, but followed a power law at higher voltages with exponent typically 2.5; the transitional voltage was directly proportional to the square of the film thickness. The results were interpreted as ohmic conduction at low voltages and space-charge-limited conductivity (SCLC) dominated by an exponential trap distribution, at higher voltage levels. Measurements of current density as a function of inverse temperature for different applied voltages in the SCLC region enabled the derivation of typical mobilities in the range of ( 7.65–10.15) × 10⁻⁵ m² V⁻¹ s⁻¹ using the results of our existing theory. This value of mobility and the derived trapping parameters were in general agreement with some earlier measurements.     

Successively pulse plated cadmium selenide films and their photoelectrochemical behaviour

In successive pulse plating, the pulse deposition is repeated after a definite duration of plating preceded by a mild cleaning of the electrode and with a fresh deposition bath for the same duration. In this study, CdSe films were deposited on Ti substrates by successive pulse plating from a bath containing CdSO₄ and SeO₂ at a current density of 80 mA cm⁻² and a duty cycle of 3·3% for a duration of 30 min. The films heat-treated to 550°C for 20 min in argon atmosphere, were polycrystalline with a hexagonal structure. At an illumination of 60 mW cm⁻², a conversion efficiency of 4·5% for the photoetched film and 1·7% for the chemically etched one were determined.     

Structural and optical characterizations of chemically deposited cadmium selenide thin films

Synthesis of cadmium selenide thin films by CBD method has been presented. The deposited film samples were subjected to XRD, SEM, UV-vis-NIR and TEP characterization. X-ray diffraction analysis showed that CdSe film sample crystallized in zinc blende or cubic phase structure. SEM studies reveal that the grains are spherical in shape and uniformly distributed all over the surface of the substrates. The optical band gap energy of as deposited film sample was found to be in the order of 1.8 eV. The electrical conductivity of the film sample was found to be 10⁻⁶ (Ω cm)⁻¹ with n-type of conduction mechanism.     

Photosensitivity and spectra of deep local states in sintered films of cadmium selenide and cadmium telluride alloys

The photoconductive and luminescence properties of non-intentionally doped and copper-doped CdSe_xTe_1−x (x=0−1) films were studied. The films were prepared by spraying an aqueous suspension of mixtures with varying composition onto ceramic substrate. Both the energy gaps determined using photoconductivity spectra and the maxima of the luminescence bands as functions of the film composition x were obtained. The correlation of the luminescence intensity and the photoconductivity with x was established. Using the decay curves of photocurrent excited under “light impact” conditions the electron capture cross-sections of the recombination centres in the films under investigation were estimated. The nature of the recombination centres in CdSe_xTe_1−x (x=0–1) films both copper free and copper doped are discussed.     

Electronic and adsorption properties of the real surface of cadmium selenide films containing indium whiskers

An investigation is made to determine how surface doping of thin semiconducting cadmium selenide films with heavy metal atoms influences their binding energy and their absorption sensitivity to oxygen. Under certain doping conditions, indium atom whiskers are formed on the surface of the films. These samples show an appreciable reduction in the oxygen binding energy with the surface and a reversible response in the interaction with oxygen at 353 K. Pis’ma Zh. Tekh. Fiz. 23, 13–17 (August 12, 1997)     

X-ray topographic studies of cadmium selenide

The perfection of single crystal platelets of cadmium selenide, as grown from the vapour phase, has been investigated by X-ray projection topography. Individual dislocations, stacking faults, fringe patterns, curvature of the lattice planes, and the effects of precipitates, have been detected. Dislocations have been identified having Burgers vectors 1/31 1¯20 and 0 0 01 with screw, edge, mixed and 60° configurations.     

Growth of cadmium selenide layers by electrodeposition

Cadmium selenide (CdSe) films have been electrodeposited from a bath containing CdSO₄ and SeO₂. The pH of the bath was around 2. The deposition was done by short circuiting different substrates like Indium Tin Oxide ITO, molybdenum, sodium selenosulphite etc. to an easily oxidizable electrode (such as Al/Cd) in an electrolytic bath. The temperature of the deposition bath was varied in the range 60 to 85 ° C. The as-grown films were characterized by X-ray diffraction and scanning electron microscopy. Electrical characterization of the ITO/ CdSe/In structure was made by studying the current-voltage characteristics. Optical absorption measurements yielded a direct band gap around 1.65eV.     

Electrochemical deposition of zinc selenide and cadmium selenide onto porous silicon from aqueous acidic solutions

An electrochemical deposition process of ZnSe and CdSe compound semiconductors from aqueous acidic solutions onto silicon substrates with porous silicon layers formed on their surfaces was studied by the voltammetry method. The experimental data obtained were compared with the deposition data onto metal and silicon substrates, and the optimal conditions for the binary compound deposition onto porous silicon were determined. Semiconductor films deposited were studied by scanning electron microscopy, X-ray diffractometry, and X-ray microanalysis. The films are shown to have the crystalline structure and a nearly stoichiometric composition with a minor Se excess. Further annealing in air for 15 min allowed the Se concentration to be decreased.     

Synthesis and characterization of poly(N-vinylpyrrolidine)-silica hybrid shell coated cadmium selenide / cadmium sulphide and cadmium selenide / zinc sulfide nanoparticles

Poly(N-vinylpyrrolidine)-silica hybrid shell coated cadmium selenide / cadmium sulphide and cadmium selenide / zinc sulfide nanoparticles were synthesized by combining the organometallic and single “step” modified Stober method. The synthesized nanoparticles were characterized by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, and a spectrofluorometer. Concluding, this report has provided important insights into the design of new water-soluble polymer silica hybrid shell coated quantum dots nanoparticles for biomedical, analytical and catalytic applications.     

Growth and characterization of lead selenide thin films

Growth of lead selenide thin films has been carried out electrochemically on indium doped tin oxide coated conducting glass substrates from an aqueous acidic bath consists of Pb(CH₃COO)₂ and SeO₂. X-ray diffraction analysis has been carried out to determine the crystal structure and phases of the deposited films. Microstructural parameters such as crystallite size, strain and dislocation density which have been evaluated from X-ray diffraction data. Surface morphology and film composition have been analyzed using scanning electron microscopy and energy dispersive analysis by X-rays. The effect of bath temperature on structural, microstructural, morphological and compositional properties of the films are studied and the results are discussed. Optical absorption measurements shows that the deposited films possess a direct band gap value of 0.38?eV.     

Electrosynthesis of the molybdenum disulphide thin films and characterization

Thin films of molybdenum disulphide have been prepared by electrodeposition from an aqueous bath by using molybdenum trioxide and sodium thiosulphate as Mo⁺ ion and S⁻² ion sources, respectively. The films deposited onto stainless steel and fluorine doped tin oxide (FTO) glass substrates were adherent to the substrate. X-ray diffraction studies show that films are polycrystalline. SEM shows films are continuos and uniform. Optical absorption gives a bandgap energy of 1.7 eV.     

High-temperature edge luminescence from cubic cadmium selenide layers

High-temperature electrical and luminescent properties of β-CdSe layers synthesized by the solid-state substitution reaction were studied. In the temperature interval from 290 to 450 K, the edge emission band related to the annihilation of free excitons inelastically scattered from free charge carriers dominates in the photoluminescence spectrum. The binding energies of the excitons and optical phonons were measured. The bandgap width and the temperature coefficient of its variation were determined.