Silicon tellurides

Monolayers can be transferred onto many different substrates. Most LB depositions have been perfonned onto hydrophilic substrates, where monolayers are transferred when pulling tire substrate out from tire subphase. Transparent hydrophilic substrates such as glass [18,19] or quartz [20] allow spectra to be recorded in transmission mode. Examples of otlier hydrophilic substrates are aluminium [21, 22, 23 and 24], cliromium [9, 25] or tin [26], all in their oxidized state. The substrate most often used today is silicon wafer. Gold does not establish an oxide layer and is tlierefore used chiefly for reflection studies. Also used are silver [27], gallium arsenide [27, 28] or cadmium telluride wafer [28] following special treatment. 

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. 

Fisher JM, Berlouis LEA, Sawers LJM, MacDonald SM, Affrosman S, Diskett DJ, Astles MG (1994) Growth and characterization of electrodeposited films of cadmium telluride on silicon. J Cryst Growth 138 86-93... 

Jackson F, Berlouis LEA, Rocabois P (1996) Layer-by-layer electrodeposition of cadmium telluride onto silicon. J Cryst Growth 159 200-204... 

Zinc telluride, ZnTe, was deposited on quartz, silicon, InAs, and GaSb substrates using Zn[TeSi(SiMe3)3]2 at temperatures between 250 °C and 350 °C. On InAs (orientation not specified) a cubic ZnTe layer was obtained. Problems of stoichiometry are encountered at temperatures below 325 °C because decomposition of the precursor is incomplete, while at higher temperatures (above 350 °C) the deposited ZnTe decomposes into Zn (which evaporates) and involatile elemental tellurium which remains. The results with the analogous cadmium precursor (1.4 torr, 290 °C) indicate that the CdTe films may be of better stoichiometry than those of ZnTe, with XRD results indicating that on a Si substrate the hexagonal phase is predominantly... 

Copper table, in silicon casting, 22 507 Copper telluride, 24 409 Copper thiocyanate, molecular formula and uses, 7 778t Copper-tin alloys, 24 796... 

A number of companies are currently involved in thin-fllm photovoltaics [17], and low-cost multilayer thin-fllm amorphous silicon and CdTe (cadmium telluride) systems have already been installed in large numbers with efficiencies of the order of 10% and of about 80% output after 25 years of operation. Large-scale plants have been announced for the so-called CIS (cadmium indium selenide) and CGIS (copper gallium indium diselenide), technologies with production efficiencies in the range 12-13% and laboratory measurements up to 19.9% [18]. 

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... 

Still another method used to produce PV cells is provided by thin-film technologies. Thin films are made by depositing semiconductor materials on a solid substrate such as glass or metal sheet. Among the wide variety of thin-film materials under development are amorphous silicon, polycrystalline silicon, copper indium diselenide, and cadmium telluride. Additionally, development of multijunction thin-film PV cells is being explored. These cells use multiple layers of thin-film silicon alloys or other semiconductors tailored to respond to specific portions of the light spectrum. 

Consequently, the bond is fully saturated for A sp = 0 with a bond order of 1, but it is only partially saturated by the time the gap closes for AEap/2 h = 1 (cf eqn (7.92)) when the bond order equals 0.76. This simple second moment model has been extended to include the compound semiconductors. The resultant values of the bond order are given in Table 7.2. We see that the bonds in tetrahedral carbon and silicon are almost fully saturated, but those in zinc selenide and cadmium telluride are only about 75% saturated due partly to the mismatch in the sp orbitals between chemically distinct atoms. 

Although conventional solar cells based on silicon are produced from abundant raw materials, the high-temperature fabrication routes to single-crystal and polycrystalline silicon are energy intensive and expensive. The search for alternative solar cells has therefore focused on thin films composed of amorphous silicon and on other semiconductor heterojunction cells (e.g., cadmium telluride and copper indium... 

On the basis of the expected charges on the monatomic ions, give the chemical formula of each of the following compounds (a) manganese(II) telluride (b) barium arsenide (c) silicon nitride (d) lithium bismuthide (e) zirconium(IV) chloride. 

Grooves 5 are formed in a substrate 1 of either cadmium telluride, cadmium zinc telluride, gallium arsenic, silicon or sapphire. A layer 4 of Hgi.yCd,Te is formed at the bottom and at the sides of the grooves. Next, the whole structure is covered by a p-type Hgi.xCd,Te layer (y < x), in which n-type regions 3 are formed. 

An imager having an element packing density of 90% is disclosed in US-A-4104674. Infrared photovoltaic detectors of mercury cadmium telluride are mounted on a silicon substrate. Electrical contacts are made by thin-film metallizations. 

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. 

A problem which arises when a read-out chip of for example silicon is attached to a detector chip of mercury cadmium telluride is the mechanical damage which may occur when the array is cooled to cryogenic temperatures for operation. The stress is due to a mismatch in the coefficients of thermal expansion between the two materials. 

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