Semiconductor molten

This work attempts to model a semiconductor/molten salt electrolyte interphase, in the absence of illumination, in terms of its basic circuit elements. Measurement of the equivalent electrical properties has been achieved using a newly developed technique of automated admittance measurements and some progress has been made toward identification of the frequency dependent device components (1 ). The system chosen for studying the semiconductor/ molten salt interphase has the configuration n-GaAs/AlCl3 1-... 

Molten silicon is not a semiconductor, and has no commercial use, although because of the high heat of fusion, it has been considered as a heat storage medium. The Hquid (molten) siUcon properties summarized in Table 6 are nevertheless of importance because these affect single-crystal growth, an operation through which essentially all semiconductor-grade siUcon must pass. 

Tellurium Selenides. TeUurium selenides or selenium teUurides are unknown. The molten elements are miscible in aU proportions. The mixtures are not simple soUd solutions but have a complex stmcture. Like the sulfides, the selenides exhibit semiconductor properties. 

It is pmdent to perform zone melting in a dry inert atmosphere. Oxygen causes most organic melts to oxidize slowly. Oxygen and moisture not only oxidize metals and semiconductors, but often enhance sticking to the container. Molten salts attack sUica more rapidly in the presence of moisture. Oxygen and water are considered impurities in some inorganic compounds. 

Molten sulphides are almost invariably semiconductors, and so their conductivities are typically larger than Arose of the average molten electrolyte. For example, the specific conductairce of molten AgaS can be described, as a function of temperature by the equation... 

Arsenic and antimony are metalloids. They have been known in the pure state since ancient times because they are easily obtained from their ores (Fig. 15.3). In the elemental state, they are used primarily in the semiconductor industry and in the lead alloys used as electrodes in storage batteries. Gallium arsenide is used in lasers, including the lasers used in CD players. Metallic bismuth, with its large, weakly bonded atoms, has a low melting point and is used in alloys that serve as fire detectors in sprinkler systems the alloy melts when a fire breaks out nearby, and the sprinkler system is activated. Like ice, solid bismuth is less dense than the liquid. As a result, molten bismuth does not shrink when it solidifies in molds, and so it is used to make low-temperature castings. 

Low-temperature solvents are not readily available for many refractory compounds and semiconductors of interest. Molten salt electrolysis is utilized in many instances, as for the synthesis and deposition of elemental materials such as Al, Si, and also a wide variety of binary and ternary compounds such as borides, carbides, silicides, phosphides, arsenides, and sulfides, and the semiconductors SiC, GaAs, and GaP and InP [16], A few available reports regarding the metal chalcogenides examined in this chapter will be addressed in the respective sections. Let us note here that halide fluxes provide a good reaction medium for the crystal growth of refractory compounds. A wide spectrum of alkali and alkaline earth halides provides... 

Water is involved in most of the photodecomposition reactions. Hence, nonaqueous electrolytes such as methanol, ethanol, N,N-d i methyl forma mide, acetonitrile, propylene carbonate, ethylene glycol, tetrahydrofuran, nitromethane, benzonitrile, and molten salts such as A1C13-butyl pyridium chloride are chosen. The efficiency of early cells prepared with nonaqueous solvents such as methanol and acetonitrile were low because of the high resistivity of the electrolyte, limited solubility of the redox species, and poor bulk and surface properties of the semiconductor. Recently, reasonably efficient and fairly stable cells have been prepared with nonaqueous electrolytes with a proper design of the electrolyte redox couple and by careful control of the material and surface properties [7], Results with single-crystal semiconductor electrodes can be obtained from table 2 in Ref. 15. Unfortunately, the efficiencies and stabilities achieved cannot justify the use of singlecrystal materials. Table 2 in Ref. 15 summarizes the results of liquid junction solar cells prepared with polycrystalline and thin-film semiconductors [15]. As can be seen the efficiencies are fair. Thin films provide several advantages over bulk materials. Despite these possibilities, the actual efficiencies of solid-state polycrystalline thin-film PV solar cells exceed those obtained with electrochemical PV cells [22,23]. 

Metals and semiconductors are common examples of electronic conductors, and under certain circumstances even insulators can be made electronically conducting, for example by photoexcitation. Electrolyte solutions, molten salts, and solid electrolytes are ionic conductors. Some materials have appreciable electronic and ionic conductivities,... 

With metals, semiconductors, and insulators as possible electrode materials, and solutions, molten salts, and solid electrolytes as ionic conductors, there is a fair number of different classes of electrochemical interfaces. However, not all of these are equally important The majority of contemporary electrochemical investigations is carried out at metal-solution or at semiconductor-solution interfaces. We shall focus on these two cases, and consider some of the others briefly. 

Zone refining is a technique for decreasing the level of impurities in some metals, alloys, semiconductors, and other materials this is particularly so for doped semiconductors, in which the amount of an impurity must be known and carefully controlled. The technique relies on the impurities being more soluble in a molten sample (like oxygen in water, as noted above) than in the solid state. 

Databases, generally available for a fee, often together with software packages, have been prepared for several types of materials and systems. Typical examples are a database developed for Fe-rich alloys containing data for up to 15 components, and 55 types of phases or similar databases for Mg-rich, Al-rich, Ni-rich, Ti-rich alloys. Other databases are available for different types of materials semiconductors, solder alloys, ceramic systems, slag, molten salts, etc. 

Once germanium is recovered and formed into blocks, it is further refined by the manufacturer of semiconductors. It is melted, and the small amounts of impurities such as arsenic, gallium, or antimony, are added. They act as either electron donors or acceptors that are infused (doped) into the mix. Then small amounts of the molten material are removed and used to grow crystals of germanium that are formed into semiconducting transistors on a germanium chip. The device can now carry variable amounts of electricity because it can act as both an insulator and a conductor of electrons, which is the basis of modern computers. 

Fig. 3.10 Mott-Schottky plot for n-type and p-type semiconductor of GaAs in AlCls/n-butylpyridinium chloride molten-salt electrolyte [79],...

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