Cadmium Sulfide Crystals Research Articles

SAW image scanner using transverse acoustoelectric effect in photoconductive CdS

Optical image scanning utilizing the transverse acoustoelectric effect induced by surface acoustic waves propagating on a basal plane of photoconductive cadmium sulfide is experimentally demonstrated. ’’Positive’’ high sensitivity is obtained by using a cadmium sulfide crystal known well to be an excellent photoconductor as well as a good piezoelectric material.

Hologram recording in cadmium and copper doped cadmium sulphide

Photoinduced changes in the optical absorption of large crystals of cadmium sulphide doped with cadmium and copper, are used to store Bragg-angle holograms by means of a He-Ne laser. The recordings are stable in the dark at room temperature and can be erased either optically or thermally. Diffraction efficiencies of over 1% at a write energy of about 1J/cm 2 are obtained.

Laser screen made of bulk cadmium sulfide and selenide single crystals

Plates cut from cadmium sulfide and selenide ingots were used as laser screens. The laser threshold was reduced considerably by chemomechanical polishing.

Excitation of cadmium sulfide crystals by electron impact in an atmospheric pulse discharge

Cadmium sulfide optical resonators were pumped at atmospheric pressure by an electron flux generated in nanosecond gas discharges. The resonators were excited at –40°C, –50°C, and at room temperature. The emission maximum was located in the region of 521 nm and its halfwidth was 1.5 nm. This pumping method could be used in the end-resonator and radiating-mirror configurations. The method could be used in nonevacuated electron-impact excited semiconductor lasers of size approaching injection lasers but capable of emitting considerably higher powers than injection lasers.

The influence of heat treatment and ambient atmosphere on the In-CdS junction photovoltage

Measurements of the conductivity, photoconductivity and photovoltage have been made on photoconducting cadmium sulphide crystals with evaporated indium contacts. Changes in the electrical properties of this system due to mild heat treatment are ascribed to changes in the contact resistance and the accompanied change in the effective value of the surface recombination velocity at the metal-photoconductor interface. A model is presented to account for the observed reversal in the sign of the photovoltage following heat treatment and to explain the sensitivity of the photovoltage to the ambient atmosphere.

Radioluminescence in large single crystals of cadmium sulphide doped with tellurium

The growth of large single crystals of cadmium sulphide doped with tellurium, CdS: Te, is reported. These crystals have a high luminescence efficiency for electron-hole recombination at isoelectronic tellurium traps. Their properties are very similar to those of platelet crystals grown in a continuous flow process. Single-photon counting techniques have been used to measure the decay of the luminescence excited by 5·5 MeV α-particles. Thermal quenching is also discussed. It is shown that a combination of a CdS: Te crystal and a silicon photodiode provides a new scintillation counter for γ ray spectroscopy.

Photoluminescence and gain of CdS and CdSe single crystals under electron-beam excitation conditions

An investigation was made of the photoluminescence spectra of cadmium sulfide and selenide single crystals (77 and 4.2°K) and of the spectra of the gain α(ħω) during excitation of the same crystals with electron beams of 20 keV energy (77°K). The experimental and calculated gain profiles were compared on the assumption of the exciton–phonon interaction between carriers. A correlation was found between the photoluminescence and gain spectra. Gains up to 70 cm–7 were obtained for CdS crystals whose 77°K photoluminescence spectra included a strong (compared with the edge luminescence) band due to A free excitons, and there was clear evidence of transitions assisted by one or two longitudinal optical phonons. In the case of CdSe crystals grown by the sublimation of a powder in an argon stream the maximum gain and full agreement between the experimental and calculated gain profiles were obtained when these crystals were grown in the temperature range 800–900°C.

The formation of cuprous sulphide on single crystals of cadmium sulphide

The rate at which a layer of cuprous sulphide is formed on single crystals of cadmium sulphide immersed in an aqueous solution containing cuprous ions has been monitored. Crystals doped with indium, gallium or copper have been studied. The growth of cuprous sulphide on crystals containing indium or gallium is governed by two parabolic laws, whereas a single parabolic law can be used to describe the rate of growth on copper-doped crystals.

Halogen impurities in CdS and ZnSe single crystals by thermal neutron activation

Halogen donors (chlorine, bromine and iodine) in cadmium sulfide and zinc selenide single crystals (vapor grown platelets with and without halogen dopants) were determined by thermal neutron activation analysis. This approach proved to be simple, rapid and highly selective. The analyzed impurity contents range from 100 ppb to several ppm. Radionuclides used for identification of chlorine, bromide and iodine were 38Cl ( t 1/2 ≈ 25 min), 82Br ( t 1/2 ≈35·1 hr) and 128I ( t 1/2 ≈ 25 min), respectively; these nuclides were radiochemically isolated and measured by gamma scintillation spectrometry. The levels of the impurities measured by this method were then used to identify new types of donor-acceptor pair line spectra and two-electron transitions accociated with chlorine, bromine or iodine impurities. The results were all in good agreement with the suspected lines, and accordingly well characterized.

EPR Spectra of Transition Element Impurities with 3d2 Configuration in Hexagonal CdS and CdSe Single Crystals

AbstractElectron paramagnetic resonance has been studied for divalent titanium with 3d2 configuration substituting for Cd in hexagonal single crystals of cadmium sulphide and cadmium selenide. The parameters of the spin‐Hamiltonian have been determined at T = 27 and 77 K. It is found that the symmetry of the centre is axial, corresponding to the C3V symmetry of an isolated impurity on normal lattice sites in wurtzite.

Current oscillations associated with impurity breakdown in photosensitive cadmium sulphide crystals

Abstract A model is proposed to explain the generation of current oscillations in CdS samples due to impurity breakdown. Some of the rules obeyed by such breakdown and current oscillations accompanying it were investigated.

Free exciton motion and exciton-phonon interaction studies using cathodoluminescence

The exciton emission spectrum of single crystals of cadmium sulphide under electron excitation has been studied and the broadening of the free exciton lines (first LO and second LO phonon assisted replicas of the n = 1 ( Γ 9− Γ 7) emission) has been interpreted in terms of free exciton motion. Observation of the variation of the half-widths of these lines with lattice temperature indicates that the effective temperature to be assigned to the excitons is distinctly higher than the lattice temperature. This phenomenon is interpreted using a perturbation theory approach within the language of second quantization and is shown to depend basically on the mode of excitation employed.

The electrical properties and growth conditions of CdS crystals

Large crystals of cadmium sulphide have been grown in various partial pressures of cadmium and sulphur vapour. The concentration and ionisation energy of the shallow donors in the different crystals have been determined by measuring the Hall coefficient and electrical conductivity of semiconducting samples, and by comparing the magnitudes of the drift and Hall mobilities in photoconducting (semi-insulating) samples. The variation of the donor and acceptor content can be explained in broad terms in relation to the parameters of crystal growth. Hall measurements indicate that the ionisation energy of the shallow donors is 0·021 ± 0·002eV. The drift mobility experiment suggests that two shallow traps are present with energy depths of 0·015 and 0·037 eV. The variation of Hall mobility with temperature over the range 30–300°K can be explained in terms of polar optical mode, piezoelectric and ionised impurity scattering. The best value of effective mass obtained was 0·19m.

The growth of group II–VI crystals in gels

Experiments relating to the gel-growth of selected group II–VI semiconductor compounds in single crystal form are described. Single lead sulphide crystals with relatively low etch pits density and a size of 1-1.5 mm have been grown in silica gels. α-mercuric sulphide crystals, 0.1-0.15 mm in size have been successfully grown in polyacrylamide gels. The growth of cadmium sulphide crystals has resulted in either spherulites or dendrites depending mainly upon the cadmium ion source used. The experimental problems associated with the successful growth of cadmium, zinc, lead and copper selenides and tellurides are discussed, and the specific proposed solutions are described. Experiments on the growth of selenides have resulted in excessive nucleation and the successful growth of these crystals, therefore, depends on a better control of supersaturation in the growth systems. Attempts to grow single telluride crystals of Cd, Zn, and Pb were unsuccessful.

Luminescence in copper-doped CdS crystals

Attempts have been made to incorporate copper into cadmium sulphide crystals during growth, which has been carried out either in an excess partial pressure of cadmium or sulphur vapour. The intensities of the four major photoluminescence bands at 0.71–0.78, 1.02, 1.57 and 1.87 μm have been studied in relation to the conditions under which the crystals were grown. It is also demonstrated that the intensities of the various bands, as measured at 85°K, depend on whether the samples have previously been illuminated at temperatures in the range 160–400°K. It is concluded that two complex centres (a self activated centre and a high energy copper centre) are responsible for the 0.71–0.78 μm emission, and that a different defect (which is either a substitutional copper ion or a complex association of copper ions and cadmium vacancies) is responsible for the remaining three luminescence bands.

Changes in the energy spectrum of trapping centres in crystals of cadmium sulphide subjected to electron bombardment: R V Grigorev et al, Uch Zap LGU, No 354, 1970, 91–96 ( in Russian)

Changes in the energy spectrum of trapping centres in crystals of cadmium sulphide subjected to electron bombardment: R V Grigorev et al, Uch Zap LGU, No 354, 1970, 91–96 ( in Russian)

Growth of single crystals of cadmium sulphide in evacuated ampoules

Large single crystals of cadmium sulphide have been grown in vacuum at comparatively lower temperatures ∽ 1025–1060 °C. A substantial rate of transport of the material to the crystal growth site has been made possible by using good stoichiometry and high purity initial charge in self-sealing ampoules. The nature of the free growing surfaces of the grown crystals have also been discussed.

Edge Emission Bands in High-Purity Cadmium Sulfide

It is shown that there are nine clearly defined series of low-temperature phonon-assisted edge emission bands in pure cadmium sulfide crystals. Of these nine series, four have not been previously discussed. It is shown that eight of the series can be explained as arising from transitions involving a band model with two donor levels and three acceptor levels.

Space-charge-limited currents in hollow crystals of cadmium sulphide

(1971). Space-charge-limited currents in hollow crystals of cadmium sulphide. International Journal of Electronics: Vol. 30, No. 3, pp. 287-289.

Anti-Stokes excited edge emission in cadmium sulphide

A detailed study has been made of the variations in the structure of the blue and green edge emission of doped and undoped crystals of cadmium sulphide under Stokes and anti-Stokes excitation. A model to explain the results is proposed, in which the key feature is the state of ionization of the centre which makes the anti-Stokes excitation process possible. The model implies that this centre is the same as that which leads to the green edge emission and to deep centre luminescence during recombination.