Optical indium compounds

The supplanting of germanium-based semiconductor devices by shicon devices has almost eliminated the use of indium in the related ahoy junction (see Semiconductors). Indium, however, is finding increased use in III—V compound semiconductors such as indium phosphide [22398-80-7] for laser diodes used in fiber optic communication systems (see Electronic materials Fiber optics Light generation). Other important indium-containing semiconductors include indium arsenide [1303-11-3] indium antimonide [1312-41 -0] and copper—indium—diselenide [12018-95-0]. 

Extensive structural, optical, and electronic studies on the chalcopyrite semiconductors have been stimulated by the promising photovoltaic and photoelectrochem-ical properties of the copper-indium diselenide, CuInSe2, having a direct gap of about 1.0 eV, viz. close to optimal for terrestrial photovoltaics, and a high absorption coefficient which exceeds 10 cm . The physical properties of this and the other compounds of the family can be modulated to some extent by a slight deviation from stoichiometry. Thus, both anion and cation deficiencies may be tolerated, inducing, respectively, n- and p-type conductivities a p-type behavior would associate to either selenium excess or copper deficiency. 

Indium-promoted reaction of l,4-dibromo-2-butyne with carbonyl compounds gives 1,3-butadiene derivatives via the allenic indium intermediates (Scheme 56).220 Similar indium-mediated l,3-butadien-2-ylation reactions of optically pure azetidine-2,3-diones have been investigated in aqueous media, offering a convenient asymmetric entry to the 3-substituted 3-hydroxy-/ -lactam moiety (Equation (40)). The diastereoselectivity of the addition reaction is controlled by the bulky chiral auxiliary at Q4 221 222... 

ICP thin films were used as driving electrodes for polymer-Dispersed Liquid-Crystals (PDLC) display devices. Liquid-crystalline-based display devices, which are commonly made of a liquid-crystal compound sandwiched between two substrates coated with a conducting layer of indium tin oxide (ITO), whose substitution with ICP electrodes could improve the optical and mechanical properties of the display devices. On the way to all-organic displays, PDLC sandwiched between two plastic substrates coated with ICP layers are promising devices for paper-like displays for electronic books which require flexibility, lightness, and low-power consumption. The electro-optical characteristics (transmission properties, drive voltages and switching times) of the PDLC devices depend on the nature of the ICP substrate used [13]. 

The choice of a suitable counter-electrode for a successful EW is not easy since only a few compounds fulfil the desired operational requirements which call for an uncommon combination of electrochemical and optical properties. The most promising, and, thus far, the mostly used materials are indium tin oxide, nickel oxide, iridium oxide and cobalt oxide among the inorganic ECMs, and polyaniline (PANI) among the organic ECMs. The electrochromic properties of indium tin oxide and PANI have been described in Chapter 7. Therefore, here attention will be mainly focused on transition metal oxide counter-electrodes. 

Indium Phosphide (InP). Indium phosphide is a direct-gap semiconductor. The conduction band minimum is situated at F. Higher conduction band minima at L and X have been detected in optical experiments. The X-band minima show no camel s back structure, in contrast to most other III-V compounds with the zinc blende structure. The valence band has the structure common to all zinc blende-type semiconductors (Fig. 4.1-113). 

Warren and co-workers have reported remarkable data on molten indium dihalides/ " In the solid state these are typical class I compounds, In(I)In(III)X4, but in molten InCl2 the optical band for In(III)---In(I)- In(II) In(II) is found at 17,000 cm" and from In NMR the nuclear relaxation rates above 400°C are interpreted in terms of the mechanism in equation (11) ... 

Semiconductors are also used in many optical devices. These tend to be so-called compound semiconductors, such as gallium arsenide (GaAs) or indium phosphide (InP) which can both emit light (as lasers and light-emitting diodes) or sense it (as photodetectors). 

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