Tellurium Substrate Research Articles

Structural properties of cadmium–zinc–tellurium substrates for growth of mercury–cadmiumtellurium solid solutions

Experimental results of the investigation and analysis of structural properties of cadmium–zinc–tellurium (CZT) substrates intended for the cadmium–mercury–tellurium (MCT) epitaxy by the methods of X-ray diffraction, selective etching, and infrared (IR) microscopy are considered. A relation between the shape and the full width at half-maximum (FWHM) of the rocking curve with structural defects, which are present in the material, is demonstrated. Precipitates and inclusions of the second phase, which are present in the substrate material in the amount of 102–104 cm–2, do not affect values of the FWHM of the rocking curve. Broadening of the rocking curve is caused by either high density of dislocations (>8 × 105) or the cellular property of their distribution. Maps of the FWHM distribution of the rocking curve for determination of structural perfection throughout the entire areas of the samples allowing evaluation of the suitability of wafers for subsequent technological process have been made.

Photoconductivity in Magnetic Field of р-Type Cadmium – Mercury – Tellurium Films Grown by Liquid Phase Epitaxy

Photoconductivity in a magnetic field is studied for Faraday geometry on the p-type cadmium – mercury –tellurium films grown by liquid-phase epitaxy on cadmium – zinc – tellurium substrates. From the magnetic-field dependence of the photoconductivity signal under the film illumination from the side of the substrate or from the side of free surface, different values of mobility of minority carriers (electrons) are obtained. It is shown that for the mathematical description of the photoconductivity signal in a magnetic field, two types of electrons – “fast” and “slow” electrons, as well as “heavy” holes can be used.

Novel optical properties of MoS2 on monolayer zinc tellurium substrate

The electronic structure and optical properties of the MoS2/ZnTe monolayer have been investigated through first-principles calculations. According to the different atoms’ parallelism, we have discussed five interface growth configurations: Te–Mo, Te–S, Hollow, Zn–Mo, and Zn–S systems. It has been shown that the monolayer MoS2/ZnTe exhibits semiconducting behavior and the band gap of MoS2 can be effectively tuned to 1.60 or 1.28 eV in MoS2 and ZnTe heterobilayer. An unexpected direct–indirect band gap transition is also observed, which is dependent on the stacking pattern and interlayer spacing on MoS2. The optical properties of MoS2/ZnTe heterobilayer reflect the phenomenon of red shift. The absorption edge of pure monolayer molybdenum disulfide is 0.8 eV, while the absorption edges of Te–Mo, Te–S, Hollow, Zn–Mo, and Zn–S systems become 0 eV. As a potential material, these provide a possible way to design effective FETs out of MoS2 on a ZnTe monolayer.

Epitaxial growth of tellurium by electrodeposition

Thin films of tellurium with a thickness up to 4 μm have been grown on monocrystalline tellurium substrates by an electro-deposition method. X-ray diffraction showed that the films deposited at 90°C with a current density of 0.5 mA/cm 2 or less were monocrystalline. Films with a blade-like structure were produced as the deposition current density was increased to 1 mA/cm 2.

Voltammetric studies of tellurium film and hydrogen telluride formation in acidic tellurite solution

The cathodic formation of highly active tellurium deposits and of hydrogen telluride in acidic tellurite solution were studied voltammetrically at gold and tellurium rotating disk electrodes with gold or silver rings. Both generation and detection of H 2Te are dependent on the activity of the tellurium substrate and the presence of Te(IV) in the solution. Electrodeposited Te in perchloric acid solution produces a very rough surface which affects the hydrodynamics of the electrode and leads to the electrochemical activity. This substrate is highly useful in the electrosynthesis of metal tellurides.

Cathodic generation of CdSe xTe 1− x at Te film electrodes

CdSe x Te 1− x films have been electrodeposited by the co-reduction of a tellurium substrate (to telluride) and soluble SeSO −2 3 (to selenide) in the presence of cadmium complexes. The tellurium film is itself initially electroplated in acidic media from tellurite. The necessary sequence of electrode reactions to allow CdSe x Te 1− x compositions to be formed is regulated by the potentials maintained in the pH 9.6 ammonia buffer-ethylene diamine tetraacetic acid solution. Photoelectrochemical spectroscopy and X-ray diffraction of annealed films were used to characterize the products. In the absence of cadmium ion, the method allows generation of known fluxes of telluride and selenide downstream of the generating electrode surface for other synthetic purposes.

Autoepitaxy of tellurium using vacuum deposition

High purity tellurium was deposited by vacuum evaporation on monocrystalline tellurium substrates obtained from Czochralski-grown single crystal ingots. Laue X-ray and SEM photographs indicated improved epitaxy with increase of substrate temperature from 90 to 190°C for Te-films deposited on (10 1 0), ( 1 2 1 0) and (0001) planes. Two types of defect were observed in the grown films. One was an absence of growth in localized regions producing pits in the film and the other clusters of blade-like needles growing radially through the overgrowth. The clusters were very numerous and appeared to be nucleated from the original substrate surface from microcontamination spots or, in the case of cleaved (10 1 0) planes, from the main cleavage steps.

Fabrication and characteristics of A Te-Se-CdO structure

A Te-Se-CdO layer structure has been fabricated by epitaxial growth of a selenium film on a monocrystalline tellurium substrate, followed by deposition of the counterelectrode by reactive sputtering from a cadmium target in the presence of a trace of air. Examination by RHEED has shown the counterelectrode to be CdO in polycrystalline form and the selenium film to be monocrystalline. The structures were found to give a maximum photovoltaic responsivity near 550 nm, at which wavelength the quantum efficiency was around 60% for a CdO thickness of 0.2 micron. The responsivity was affected by the CdO film thickness and the contacts to it but was insensitive to conditions relating to the selenium film, with variations in the thickness up to 10 microns, in the orientation between the (0001) and\((10\overline 1 0)\) planes and in the polishing conditions of the tellurium stustrate. Values of equivalent series and shunt resistance were determined from output current-voltage results by curve fitting and the shunt resistance was found to vary inversely with illuminance.

Selenium films epitaxially grown on tellurium substrates

The crystallinity of vacuum-deposited selenium films on clean surfaces of single crystal tellurium has been studied by reflection high energy electron diffraction (RHEED). Abrasive polishing of tellurium substrates was found to produce microscopically rough surfaces with polycrystallinity superimposed in some cases on a monocrystalline background, as indicated by RHEED patterns. Chemically prepared surfaces in the (1010) and (0001) planes, obtained by solvent cutting and polishing with chromic acid mixtures, followed by treatment with dilute hydrochloric acid, were found to be essentially free of contamination and of good crystallinity. Prolonged exposure of such surfaces to air produced a layer of contamination, but this was readily removed by heat treatment at 130°C in vacuum. Deposition of selenium under controlled conditions on the (1010) planes produced microscopically smooth monocrystalline films. For selenium deposited on (0001) substrates, good monocrystallinity was also observed but the outer surface was found to be surface faceted, giving rise to transmission type electron diffraction patterns. Scanning electron microscope examination of what appear to be “microcrack” patterns on (0001) selenium films has shown them to consist either of lines of triangular etch pits or of true microcracks.

Single Crystal Growth of Se-Te Alloys onto Tellurium from the Melts

The method to obtain single crystals of Se-Te alloys is developed. In this method, it is possible to grow a single crystal of an alloy from the melt, using a single crystal of tellurium as a seed for a Bridgmanlike method. The crystal is grown epitaxially onto tellurium. The obtained crystals is homogeneous except the layer of a few mm thick on the substrate. Single crystal growth at reasonable rates is limited to the alloys containing less than about 30% tellurium because of constitutional supercooling problem. The cross area of an ingot obtained by this method is the same as that of a tellurium substrate, whose large crystal is prepared comparatively easily, and 30 mm long alloy crystals of 12×15 mm2 cross area are obtained easily.

Crystalline Morphology and Electrical Properties of Selenium Epitaxilly Grown on Tellurium

Trigonal selenium single crystal was grown epitaxially on (0001) and (101̄0) tellurium substrates by evaporation. The dependence of the crystalline morphology on the substrate temperature and the growth rate has been studied. In the case of (0001) substrate, four kinds of selenium film were obtained: of amorphous, polycrystal of large grain, polycrystal of small grain, and single crystal. The electrical properties of single crystal formed by this method depend on the growth condition. In the best sample obtained in this experiment, the conductivity is 1.5×10-5 Ω-1 cm-1, acceptor density 5×1014 cm-3, and mobility 0.2 cm2 V-1 sec-1. These values are almost equal to those of single crystals grown from vapor or liquid phase. This paper also describes the result of study of the effects of doped bromine and thallium on the crystal growth and electrical properties.

Crystal growth phenomena in the selenium-tellurium system

Crystal growth from the liquid and from the vapor phase has been investigated over the full range of the Se-Te system. Viscosity measurements indicate that single crystal growth should be possible at reasonable growth rates only at the high tellurium end of the system. Constitutional supercooling calculations show that this limits single crystal growth at reasonable growth rates to the high selenium (∼95%) (percentages refer to atomic percentage throughout) and high tellurium (∼95%) concentrations. Experimentally it was found that single crystals could be grown at 1 mm/hr with 0 to 5% selenium before cell growth became important. Further increases in selenium concentration lead first to dendritic growth and massive segregation, and then to spherulitic growth from about 70% to 100% selenium. Single crystals could, however, be grown at 96 to 100% selenium by doping the melt with specific impurities to reduce the viscosity. Single crystal films were grown over the whole concentration range by epitaxial growth on a (10 1 ¯ 0) tellurium substrate. Electron microscopy showed that all the single crystals were homogeneous and no microsegregation or superlattice formation was present.