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.     

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.     

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.     

Irradiation induced intrinsic excitonic luminescence in cadmium telluride

Four new, sharp excitonic lines (B₁ to B₄) dominate the luminescence of CdTe, after low temperature electron irradiation. We show that they are of intrinsic nature. Two thresholds (195 keV, 280 keV) are attributed to Cd displacement and to formation of close Frenkel pairs with different configurations. Another higher threshold (480 keV) is associated with the formation of a more complex defect. All the lines disappear completely in three annealing stages at 50 K, 70 K, 140 K. The dominant lines B₁, B₂ are tentatively related to excitons bound to isoelectronic Cd vacancy/Cd interstitial close pairs.     

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.     

Thermostimulated currents in p-type cadmium telluride single crystals

Ssveral samples of CdTe were measured in a temperature range of –190C to 100C. The activation energies of the levels and their cross-section were determined. With some samples it was found that for more rapid heating the maxima of the curves of thermostimulated currents are shifted towards lower temperatures. Altogether three trap levels were found.     

Mode-locked fiber laser with a manganese-doped cadmium selenide saturable absorber

We demonstrate the generation of mode-locked pulses in an erbium-doped fiber laser(EDFL) by using a new manganese-doped cadmium selenide quantum-dots-based saturable absorber. The laser produces a soliton pulse train operating at 1561.1 nm with a repetition rate of 1 MHz, as the pump power is varied from 113 to 250 m W.At the maximum pump power, we obtain the pulse duration of 459 ns with a signal-to-noise ratio of 50 dB.     

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.     

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.     

Passivation of high-resistivity cadmium telluride by hydrogen implantation

Cadmium telluride crystals grown by the Travelling Heater Method (THM) technique have been implanted with hydrogen using protons from 2 keV to 3 MeV.Electrical measurements indicate drastic changes in the concentration of defects, especially in the 0.15–0.20 and 0.45–0.60 eV bands. However, the modification induced by hydrogen depends on the starting material, implantation and annealing conditions.Furthermore, resistivity and carrier lifetime are also strongly affected by this treatment.     

Pulse plated cadmium telluride films and their characteristics

Cadmium telluride thin films were deposited on conducting glass and titanium substrates by the pulse plating technique at different duty cycles in the range 10–50%. The films were characterised by X-ray diffraction and were found to possess single phase cubic structure. Optical studies indicated a direct band gap of 1.45 eV. Surface morphology of the films indicated that the crystallite size increases with increase of duty cycle. X-ray photoelectron spectroscopy studies confirmed the formation of CdTe. Electron-dispersive X-ray studies were made to estimate the composition. Cross-plane resistivity measurements indicated that the resistivity decreases with increase of duty cycle.     

Free carrier concentration and conductivity in chlorine doped lead telluride

Plasma resonance in the IR reflection spectra is used to measure the concentration and relaxation time of free charge carriers along with the conductivity in PbTe_{1 − x} Cl _x solid solutions. It is found that with increasing the chlorine concentration, the electron concentration and conductivity increase and reach saturation at x = 0.03 (n = 5.5 × 10¹⁹ cm⁻³, σ = 3750 Ohm⁻¹ · cm⁻¹). The relaxation time decreases with increasing the chlorine concentration and reaches the minimum value of 2.2 × 10⁻¹⁴ s at x = 0.03; then, it almost does not change.     

A mechanism for the anomalous photovoltaic effect in cadmium telluride

The anomalous photovoltaic effect has been studied in CdTe films and the results related to surface photovoltage measurements on cleaved crystals. A new model, based on surface photovoltages in angled microcrystallites is presented and accounts for the observed effects.     

The localised modes due to P defects in cadmium telluride

Dutt and Spitzer experimentally observed the localised vibrational modes related to the phosphorus defects in CdTe andr eported that P would go either to substitutional or interstitial site. In this paper we have theoretically investigated the P defect behaviour in CdTe for those two possible sites by Green’s function technique and we believe from our calculations that P goes interstitially rather than substitutionally.     

Magneto-Luminescence of excitons bound to neutral acceptor in cadmium telluride

The radiative recombination of excitons bound to neutral acceptor (A⁰, X) in high-purity CdTe has been investigated in magnetic fields up to 100 KG. A doublet structure observed in (A⁰, X) emission line is explained by considering the j-j coupling between two holes and an electron. Zeeman splittings in emission lines originate from the transition between J = 1/2 and 3/2 states in bound-exciton complex, and the acceptor-ground state. It is supposed that the acceptor which binds excitons is due to certain complex having C_3υ symmetry which is lower than the host lattice.