Cadmium Sulfide Crystals Research Articles

The role of dissociation in the growth of cadmium sulphide crystals

Growth and atomic absorption experiments are reported. It is shown that when CdS is sublimed in an atmosphere of nitrogen, small proportion of the vapour consists of undissociated material. The growth of CdS crystals occurs from this undissociated, molecular component.

Field effect and the role of excitons in the photoconductivity of CdS

For many crystals of cadmium sulfide, the photoconductivity spectrum contains a great deal of structure due to excitons. In particular, two types of spectra have been found: type I, wherein photoconductivity maxima correspond to absorption maxima, and type II, wherein photoconductivity minima correspond to absorption maxima. Various methods have been used to change one type of response into the other, among them, heat treatment, mechanical surface treatment, electron bombardment, and ultraviolet irradiation. The evidence presented in this paper supports the view that the common denominator in all these treatments is the change in the electric field near the surface. The surface field is a sensitive function of defect concentration, adsorbed oxygen, and free carrier concentration.

Intensity Relations in Laue Case Reflections of Perfect Crystals Containing Nearly Monochromatic Lattice Vibrations

AbstractA dynamical theory for the intensity relation of Laue case X‐ray reflections in the presence of nearly monochromatic lattice vibrations is developed. The results are compared with intensities diffracted from vibrating cadmium sulphide crystals excited by the acousto‐electric effect. A good agreement is obtained so that a useful method can be proposed for the measurement of vibration amplitudes.

Acoustoelectric interaction and the drift mobility of holes in CdS

A second saturation in the current-voltage characteristics of crystals of cadmium sulphide under conditions of i.r. quenching of photoconductivity is attributed to the acoustoelectric interaction of free holes and the piezoelectric lattice modes. This leads to a value of hole mobility of 48 cm2V-1 sec-1. On a observé que pendant l'amortissement de la photoconductivité par lumière infra-rouge, les caractéristiques courant-tension des cristaux du souffre du cadmium montrent une deuxième saturation qui est expliquée par un interaction entre les trous libres et les modes piézoéléctriques du réseau. On a déduit une valeur de 48 cm2c-1 sec-1 pour la mobilité des trous.

Amplification of Rayleigh Waves in cadmium sulphide crystals: Vikorov, I.A., Soviet Physics—Acoustics, Vol 14, No 3 (January–March 1969) pp 392–394

Amplification of Rayleigh Waves in cadmium sulphide crystals: Vikorov, I.A., Soviet Physics—Acoustics, Vol 14, No 3 (January–March 1969) pp 392–394

Excitation and Detection of Surface Elastic Waves in Piezoelectric Crystals

The amplitude of the surface elastic wave produced by the application of an alternating voltage to an interdigital arrangement of electrodes on the surface of a piezoelectric medium is determined. The electric field produced by the surface electrodes is calculated subject to the assumption that the piezoelectric coupling of the material can be neglected. This electric field acts as the forcing term for the inhomogeneous elastic equation, which is then solved to obtain the amplitude of the surface wave generated by the transducer. A reciprocal relationship between the excitation and detection problems is used to obtain the power extracted from the surface wave by an interdigital arrangement of surface electrodes. Measurements made on single crystals of quartz and cadmium sulfide are found to be in good agreement with theoretical predictions. The maximum value of the product (efficiency×fractional bandwidth) for a surface-wave transducer is calculated. For an interdigital surface-wave transducer on the basal plane of CdS, the maximum value of this product is found to be 7.8×10−2. It is shown that one can connect linear pairs of surface electrodes in an appropriate binary code so as to obtain high efficiency and large bandwidth transducers.

The structure and growth of hollow conical single crystals of cadmium sulphide

Single crystals of CdS were grown from the vapour phase under varied conditions to detect the presence of growth faults and polytypic structures analogous to those exhibited by ZnS. No polytypism was found as all crystals displayed only the 2H structure. The addition of a little CdI 2 as impurity during crystal growth resulted in the formation of hollow conical single crystals with no change in the structure. The possible mechanism for growth of these crystals is discussed.

Edge Emission Bands in Cadmium Sulfide

It is shown that there are five clearly defined series of edge emission bands in pure cadmium sulfide crystals. These series have their zero phonon peaks at 5128, 5140, 5163, 5179, and 5234 A at 4.2°K. The temperature dependence of the peak wavelengths and intensities of these series is discussed and a band model presented.

Impurity Conduction in Cadmium Sulfide at Low Temperatures

Impurity conduction has been investigated in three types of cadmium sulfide crystals, that is, Cl-doped cadmium sulfide, undoped cadmium sulfide grown from the vapour phase, and undoped cadmium sulfide grown by the melt. The crystals of Cl-doped cadmium sulfide exhibit the characteristics of impurity conduction at low temperatures which are similar to those of n -type germanium and n -type silicon: A metallic impurity conduction occurs above the excess donor concentration of 2×10 18 cm -3 . The concentration range between 4×10 16 cm -3 and 2×10 18 cm -3 is intermediate between metallic type and non-metallic one. A negative magnetoresistance effect is observed at the excess donor concentrations above 2×10 18 cm -3 in the temperature range from 1.5°K to 4.2°K.

Dynamic behavior of indium contacts with single crystals of cadmium sulfide above room temperature

Dark-current relaxation is observed with single crystals of cadmium sulfide after voltage has been applied. The kinetics of this reaction have been measured with respect to voltage and temperature. The observations are explained from the viewpoint of filling and emptying of electron traps in the contact regions of the crystals.

Optically Active Lattice Vibrations in Wurtzite-Type Crystals of Zinc Oxide and Cadmium Sulfide

By the use of a set of equations previously derived by Tsuboi and a set of Raman data recently published by Damen, Porto, and Tell, a set of reasonable values of force constants in the wurtzite-type ZnO and CdS crystals has been obtained. It was shown that, in the infrared-active A1- and E1-type vibrations, an appreciable amount of electrostatic force is involved besides the short-range interatomic forces through the chemical bonds. Such an electrostatic force is considered to be caused by a macroscopic polarization due to an in-phase displacement of the ions in the crystal in question, and this should not be involved in the infrared-inactive E2-type vibrations. The amount of this particular electrostatic force has also been estimated.

Growth of single crystals of cadmium sulphide

A method is described in which CdS crystals can be grown in controlled atmospheres of the constituent elements. The growth rate and growth direction are strongly influenced by the atmosphere, as is the incidence of macroscopic voids and internal strain in the crystals. These and other problems are discussed. The photoconductive and luminescent properties of the crystals are described briefly. It is shown that although growth in high partial pressures of sulphur introduces numerous acceptor levels ∼0.16 eV above the valence band, they are automatically compensated by the introduction of an equivalent concentration of shallow donors.

Growth of cadmium sulphide crystals from reacting solutions

The growth of small crystals of cadmium sulphide from reacting solutions, i.e. homogeneous precipitation, mainly at room temperature using various substrates and seed crystals is described. The influence of the cadmium salt anion is discussed in relation to the nature of the crystals obtained and also with respect to the formation of cubic or hexagonal cadmium sulphide. The hypothesis that the crystal phase precipitated is determined by the nature of the cadmium containing ion present is proposed.

Electrical Conductivity of Cadmium Sulfide under High Pressure and High Temperature

The electrical resistance of a single crystal of cadmium sulfide was measured at pressures up to 40kbar and at temperatures up to 700°C in a cubic compact anvil high pressure apparatus.The electrical conductivity of CdS of either the atmospheric wurtzite phase or the high-pressure rock salt phase is semiconductive. In the high-resistivity samples used in the present experiment the electrical resistance increased with pressure in either phases, the wurtzite or the rock salt. From the measurements of electrical resistance as a function of temperature, it is found that a band gap of CdS of the wurtzite phase is about 2.5eV. For the CdS of the rock salt phase a band gap of about 0.8eV is obtained.

The growth of homogeneous mixed crystals of zinc cadmium sulfide

Homogeneous mixed crystals of zinc cadmium sulfide have been grown from the vapor phase using the self-sealing method of Piper and Polich. Single crystals of approximately 25mm 3 in volume have been obtained, for zinc to cadmium ratios from about 0.4 to 0.7. The optimum growth parameters are given and interpreted in terms of the corresponding parameters for undoped zinc sulfide.

PHOTOLUMINESCENCE EFFICIENCY AND PHOTOCONDUCTIVITY IN CADMIUM SULFIDE

The photoluminescence efficiency and photoconductivity response of high-purity cadmium sulfide crystals were measured and interpreted in terms of a simple model involving only the donor and acceptor levels previously established, an effective surface recombination velocity, and a bulk nonradiative recombination rate. The measurements at 64 and 78 °K included the effects on the photoluminescence efficiency of varying the excitation intensity and the wavelength of the excitation light, applying electric fields, removing chemically adsorbed oxygen ions from the surface, and of different acceptor concentrations. It was established that the surface does play an important role in reducing the photoluminescence efficiency and photoconductive response, and that the photogenerated carriers do not diffuse significantly into the interior of the crystal.

Dislocations and their origin in cadmium sulfide crystals grown from the vapour phase

The type and arrangement of dislocations have been studied by means of X-ray topography. The majority of the crystals contain edge dislocations with Burgers vectors of the type b = 〈0001〉 in densities of 0 to 100 cm -2. Higher defect densities have been found in crystals which grow together with neighbouring ones. Besides the typical edge dislocations numerous dislocations occur which have Burgers vectors parallel to the basal plane. In this case there is evidence that the defects are due to plastic deformation, caused by stresses which arise between the joints during the cooling phase. Dislocations in crystals without regions of inter-growth seem to be generated by internal stresses around segregations of impurities. A multiplication process is discussed, based on combined climb and glide, presumably in the presence of a surplus of cadmium. No indications for a stimulation of the growth process by dislocations have been found.

Relaxation Type Oscillations in a High Conductive Cadmium Sulfide Crystal

Relaxation Type Oscillations in a High Conductive Cadmium Sulfide Crystal

Kinetics of the Vapor Growth of II-VI Compounds Crystals

Theoretical and experimental studies have been made of the vapor growth of the II-VI compound crystals by a modified Piper method. As a typical example, single crystals of cadmium sulphide have been grown and the growth rates observed on various conditions. It has been found that the rate is approximately proportional to the inverse of argon pressure in its atmosphere and considerably suppressed by an excess vapor of the constituent element, in particular, cadmium. Growth kinetics for the II-VI compound crystals has been developed on the basis of the mechanism that the growth proceeds via three steps: vaporization of the source material, diffusion of the vaporized species, and condensation onto the crystal surface. The theoretical formulas thus obtained have quantitatively well reproduced the experimental results. It has been concluded that the rate-determining step is the diffusion of the vaporized species. An examination of the vapor pressure has revealed that this condition is necessary for the growth of large single crystals, together with a temperature profile sublinear along the crucible axis.

Generation and amplification of an ultrasonic signal in cadmium sulphide crystals with a depletion layer

Generation and amplification of an ultrasonic signal in cadmium sulphide crystals with a depletion layer