Crystalline Tellurides

Commercially available PV systems most often include modules made from single-crystal or poly-ciystalline silicon or from thin layers of amoiphous (non-crystalline) silicon. The thin-filni modules use considerably less semiconductor material but have lower efficiencies for converting sunlight to direct-current electricity. Cells and modules made from other thin-filni PV materials such as coppcr-indiuni-diselenide and cadmium telluride are under active development and are beginning to enter the market. 

Antimony telluride films have been grown from antimony(III) and tellurium(IV) oxides.167 Antimony telluride films were stoichimetric and consisted of nanoscale particles of the size 100 nm. The films had a good crystallinity.167 Indium selenide films were grown from indium sulphate and selenium oxide precursors.168 The films consisted of large particles, 70 to 200 nm in diameter. The band gap was 1.73 eV.168... 

Diaryltellurium dihalides (general procedure) The diaryl telluride dissolved in a small amount of benzene or CHCI3 is treated dropwise, while cooling (ice bath) and stirring, with a solution of an equimolar amount of SO2CI2, Br2 or I2 in the same solvent (in the case of SO2CI2, evolution of SO2 is observed). By addition of a large excess of petroleum ether at 30-60°C (50 mL for 1 mmol) the dihalide precipitates as a crystalline solid (the dichlorides are colourless, the dibromides yellow and the diiodides red). The yields are quantitative. 

Various inorganic semiconductors (p-type and/or n-type nonoxide semiconducting materials) sucb as amorphous or crystalline silicon (a-Si or c-Si), gallium arsenide (GaAs), cadmium telluride (CdTe), gallium phosphide (GaP), indium phosphide (InP), copper... 

Reaction with tellurium powder in alkaline solution yields red crystalline zinc telluride, ZnTe. 

Another group of methods involves the conversion of the tellurium into some compound, inorganic or organic, which can be purified and then made to regenerate the element. Hydrogen telluride,7 crystalline telluric acid,8 basic tellurium nitrate 9 and diphenyl telluride 10 have all been made use of. 

Crystalline Tellurium. — Molten tellurium solidifies to a brittle, silvery, crystalline mass, which is easily powdered. The crystalline modification can also be obtained by sublimation of the element or by its slow formation, for example in the gradual decomposition of hydrogen telluride5 or in the slow atmospheric oxidation of an aqueous solution of an alkali telluride.6 When obtained of appreciable size the crystals are generally found to be prismatic, of the trigonal system, and isomorphous with metallic selenium (a c=l 1-3298 a=86-8°).7... 

HESSITE. A mineral telluride of silver. AgyTe. with some gold, crystallizing in the monoclinic syslem at normal temperatures isometric system above I49.5F (65.3 C). Crystalline form not ohvious at normal temperatures. Hardness. 2-3 specific gravity. 8.24-8.45 color, gray with metallic luster opaque. Named after G.H. Hess (1802— 1850). 

Elemental tellurium and methylene iodide yield di-iodomethyl tellurium di-iodide, M.pt. 131 C., which may be reduced by potassium metabisulphite to di-iodomethyl telluride, a yellow crystalline substance which changes to an orange polymeride at temperatures above 75° C. 

Diphenyl benzyl tellurium bromide,1 (CeH5)2(C6H5.CH2)TeBr, from diphenyl telluride dissolved in benzyl bromide, forms a crystalline mass, M.pt. 90° to 91° C., converted by silver hydroxide into the corresponding hydroxide, a yellow oil, very soluble in water, and yielding a sparingly soluble picrate on treatment with picric acid. 

The lattice mismatch between silicon and mercury cadmium telluride makes it difficult to grow an epitaxial crystalline layer of mercury cadmium telluride on silicon. In EP-A-0343738 an imager is formed by growing mercury cadmium telluride on a sapphire substrate at openings formed in a silicon layer which has been grown on the sapphire substrate (silicon-on-sapphire, SOS) at an earlier stage. 

The diaryl or aryl alkyl tellurides are dense yellow oils or crystalline solids, which are easier to handle than the dialkyl tellurides of similar molecular weight. Some of the diaryl derivatives are almost odorless solids. The same comments are valid for the diorganoditellurides 4, which are dark red oils (aliphatic derivatives) and dark red solids (aromatic derivatives). It is recommended that solutions of tellurides or ditellurides should not be kept in contact with air, since an amorphous white solid will form after some time. For some compounds, this reaction with oxygen is very fast. Aliphatic derivatives are more air sensitive than the aromatic ones. In view of this fact, it is recommended to bubble nitrogen into the solutions while a column or thin-layer chromatographic separation is performed. Evaporation of the solvent, however, minimizes the air oxidation. Pure liquids or solids can be handled in air with no need for special precautions, but prolonged exposure to air and to ambient light should be avoided. 

Cobalt Sesquitelluride is obtained in the hydrated form, Co2Te3.4H20, as a black precipitate when a solution of sodium telluride is added to one of cobalt acetate in dilute aqueous acetic acid.1 Hydrochloric and sulphuric acids are without action upon it, but nitric acid effects its oxidation. At 200° C. it loses water, and at red heat, tellurium if heated till no further loss in weight occurs, Cobalt Mono-telluride, CoTe, is obtained as a grey, crystalline substance of metallic lustre.2... 

Platinum Ditelluride, PtTe2, results on heating an intimate mixture of finely divided platinum with a slight excess of tellurium above that theoretically required.1 The product is treated with concentrated potash solution to remove excess of tellurium, and the telluride remains as a grey, crystalline, insoluble powder. 

Potassium tellurides.—The monotelluride, K2Te, was originally produced by Davy12 by direct combination of the elements. At 250° C. the reaction is even more energetic than that between sodium and tellurium. When prepared in an atmosphere of hydrogen, the product has a crystalline structure, and a dark iridescent-purple colour. With water it yields a purple solution, being reprecipitated by alcohol in the form of small, ill-defined crystals.18... 

Iron combines with tellurium when the two elements are heated together in an inert atmosphere, yielding ferrous telluride,2 FeTe, as a hard grey crystalline mass. Stable in moist air, it is but slowly attacked by acids in the cold, although bromine water readily effects its solution.3... 

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