On the properties of real cadmium telluride surfaces

Optical and electrical properties of lapped, mechanically polished, and etched cadmium telluride surfaces have been studied by ellipsometry, infrared transmission, reflectivity, and sheet resistance measurements. They have been related to the characteristics of Schottky barriers realized by deposition of gold on these surfaces. These experiments indicate that the electrical behaviour of devices made of cadmium telluride critically depends on the surface damages produced during the sample preparation: while good diodes can be made when bromine in methanol etching is used, lapping and polishing produce a disturbed layer of poor electrical and optical properties whose thickness is related to the size of the abrasive powder used during the preparation.     

Study of rectifying and photoelectric properties of barrier structures based on vanadium-doped cadmium telluride

Structures similar to Schottky diodes are prepared by the thermal evaporation of chromium on high-resistivity cadmium telluride substrates doped by vanadium (CdTe: V) to a concentration of 5×10¹⁸ cm⁻³. The current-voltage and spectral characteristics of the Cr/CdTe: V barrier structures are studied, and their rectifying properties are evaluated.     

Optical properties of zinc telluride with cadmium telluride submonolayers

Reflection, luminescence, and Raman spectra of epitaxial ZnTe layers nominally incorporating double CdTe submonolayers were studied. The band of an exciton localized at the potential produced by narrow-gap planar inclusions dominated the luminescence of these heterostructures. The emission parameters of localized excitons (specifically, the ratio of integral emission intensity to localization energy) were determined, and it was found that excitons interact with longitudinal optical phonons of the layer enriched with cadmium. Giant amplification of the Stokes component resonant with the localized exciton level was observed in Raman scattering.     

Optical and structural properties of fullerene films doped with cadmium telluride

Composite thin-film structures based on C₆₀/CdTe were prepared by discrete vacuum evaporation in a quasi-closed volume and by vacuum evaporation from a Knudsen cell. The synthesized fullerene samples contained cadmium telluride with a content ranging from 1 to 50 wt %. The morphology and composition of the films were controlled using scanning electron microscopy and energy-dispersive X-ray analysis. The optimum geometry, the total energy, and the spectrum of excited states of the fullerene-cadmium telluride molecular complex were calculated by quantum-chemical methods. The spectral dependences of the photo-luminescence, Raman scattering, extinction coefficient, and refractive index were measured for different compositions. It was found that, in contrast to the spectra of pure fullerene, the luminescence and absorption spectra of the fullerene doped with cadmium telluride exhibit an additional peak in the wavelength range of 600–620 nm. These data were interpreted as the existence of dipole-allowed transitions in the spectrum of excited singlet states of the fullerene due to the interaction with cadmium telluride. The composite films had an increased resistance to degradation under the action of oxygen and water vapor.     

Preparation and electrical properties of copper-doped cadmium telluride single crystals

Preparation and the electrical properties of copper-doped cadmium telluride single crystals prepared by directional freezing and by diffusion of copper from a layer of Cu₂ Te are described in this paper. The dependence of electrical properties on the preparation mode is followed. In the enclosed infra-red spectra it is proved that samples suitable for optical measurements can be prepared by both described techniques.     

Preparation and photoelectric properties of cadmium sulfide quantum dots

Cadmium sulfide quantum dots(CdS QDs) are widely used in solar cells, light emitting diodes, photocatalysis, and biological imaging because of their unique optical and electrical properties. However, there are some drawbacks in existing preparation techniques for CdS QDs, such as protection of inert gas, lengthy reaction time, high reaction temperature, poor crystallinity, and non-uniform particle size distribution. In this study, we prepared CdS QDs by liquid phase synthesis under ambient room temperature and atmospheric pressure using sodium alkyl sulfonate, CdCl_2, and Na_2S as capping agent, cadmium, and sulfur sources respectively. This technique offers facile preparation, efficient reaction, low-cost, and controllable particle size. The as-prepared CdS QDs exhibited good crystallinity, excellent monodispersity, and uniform particle size. The responsivity of CdS QDs-based photodetector is greater than 0.3 μA/W, which makes them suitable for use as ultra-violet(UV) detectors.     

Effect of annealing on the structural properties of arsenic-implanted mercury cadmium telluride

Effect of annealing on the structural properties of arsenic-implanted mercury cadmium telluride film grown by molecular beam epitaxy was studied with the use of transmission electron microscopy and optical reflection. Strong influence of the graded-gap surface layer grown on top of the film on the behaviour of implantation-induced defects under arsenic activation annealing was revealed and interpreted.     

Semiinsulating layers of cadmium telluride

Tin diffusion into cadmium telluride substrates having different types and values of conductivity is used to fabricate layers with a resistivity of ∼10¹⁰ Ω cm at 300 K.     

Electrical and thermoelectric properties of antimony telluride and cadmium sulfide films

Films of p-type Sb₂Te₃ and of n-type CdS have been examined for Hall effect, electrical conductivity, and differential thermo-emf; concentration, mobility, and activation energy are derived. The mobility in CdS is increased by indium doping.     

Study of molecular beam epitaxy of cadmium telluride on sapphire

The effect of thermal treatment of (0001) sapphire substrates on the structure of cadmium telluride films grown by molecular beam epitaxy was investigated. The growth process was carried out on a laboratory facility equipped with a mass spectrometer and electron diffractometer. It was established that no annealing or annealing in vacuum (P < 0.13 Pa) results in the growth of polycrystalline CdTe films. Epitaxial CdTe films with a cubic structure of the sphalerite type oriented with the (111) plane parallel to the substrate grow on the substrates annealed in air at T > 1000°C. Electron diffraction patterns showed that they have a mosaic structure and contain twins with the 〈111〉 twinning axis. Atomic-force microscopic images revealed CdTe crystallites with lateral sizes of ∼50 nm arranged along the steps on the sapphire substrate surface. These results allowed the conclusion to be drawn that the growth of CdTe on sapphire substrates can occur by the formation of the three-dimensional nucleation centers according to the Volmer-Weber mechanism.     

Current carrier mobility in manganese-doped cadmium telluride

The possibility of substantial influence of a manganese impurity on the magnetic and optical properties of CdTe, which is explained by the state and interaction of the Mn 3d⁵-electron spins in the CdTe crystal lattice, is shown in [1–3]. An investigation of the influence of the Mn impurity on current carrier scattering in this material is of interest. To this end, the temperature dependence of the Hall mobility of electrons in CdTe-Mn single crystals is investigated in this paper in the temperature range 77–435°K.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 24–28, April, 1982.     

Compensating effect of Sn impurity in cadmium telluride

The equilibrium characteristics of CdTe:Sn crystals grown by the Bridgman method are investigated. The impurity content in the samples was in the range N_Sn=10¹⁶-10¹⁸ cm^–3. It is established that for a specific (critical) Sn concentration (N_cr) a sharp increase in the resistivity occurs and the material becomes semi-insulating with n-type conductivity. The value of N_cr is determined (7·.10¹⁶ cm^–3). No correlation is noted between the properties of the semi-insulating CdTe:Sn samples and the impurity content. The effect of heat treatment (800°C, P_Cd=min) on the properties of the semi-insulating CdTe:Sn samples is studied, and it is established that the equilibrium characteristics of the crystals (mobility, carrier concentration) are practically unchanged.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 66–69, April, 1986.     

The effect of crystal structure on the photoelectric properties of thin cadmium sulfide layers

The results presented are of an investigation into the photoelectric properties of polycrystalline cadmium sulfide layers obtained by thermal evaporation in vacuum. In producing the layers the substrate temperature was varied over the range 80 °–500 ° C, and in addition the layers were heated in air. It was found that the spectral distribution of the photocurrent, the absolute and relative phbtosensitivity, and the relaxation time depend to a marked extent on the substrate temperature. These differences are connected with a change in the degree of defectiveness and phase compositions of the polycrystalline cadmium sulfide layers.     

Electrophysical characteristics of epitaxial cadmium telluride films

Equilibrium electrophysical characteristics of epitaxial CdTe films grown by the thermal screen method and the quasiclosed volume method are investigated. It is established that the films in both cases are semiconductors with inhomogeneous potential relief of the band to whose formation the main contribution is from barriers on the boundaries of the growth patterns. It is shown that jump conductivity with a variable jump length due to inhomogeneity of the potential relief of the bands and the high states density at the Fermi level is observed in CdTe films synthesized by the quasiclosed volume method for relatively high temperatures.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 72–76, March, 1990.     

The influence of copper oxidation on the photoelectric properties of Cu-activated polycrystalline cadmium selenide

The photoelectric properties of Cu-activated polycrystalline CdSe are studied. It is shown that during the heat treatment of the cadmium selenide with copper, cuprous oxide may be formed in intercrystalline layers, which significantly affects the spectral distribution of the photoconductivity, the integral sensitivity, and the time constant of the sample. When the copper is introduced by way of CuCl₂ solution, however, the polycrystalline CdSe is activated with no noticeable formation of cuprous oxide.     

Laser induced damage studies in mercury cadmium telluride

We have investigated laser induced damage at laser wavelength in diamond paste polished (mirror finish) and carborundum polished Hg_0.8Cd_0.2Te (MCT) samples with increasing fluence as well as number of pulses. Evolution of damage morphology in two types of samples is quite different. In case of diamond paste polished samples, evolution of damage morphological features is consistent with Hg evaporation with transport of Cd/Te globules towards the periphery of the molten region. Cd/Te globules get accumulated with successive laser pulses at the periphery indicating an accumulation effect. Real time reflectivity (RTR) measurement has been done to understand melt pool dynamics. RTR measurements along with the thermal profile of the melt pool are in good agreement with thermal melting model of laser irradiated MCT samples. In case of carborundum polished samples, laser damage threshold is significantly reduced. Damage morphological features are significantly influenced by surface microstructural condition. From comparison of the morphological features in the two cases, it can be inferred that laser processing of MCT for device applications depends significantly on surface preparation conditions.