Device Physics of Narrow Gap Semiconductors
Narrow gap semiconductors obey the general rules of semiconductor science, but often exhibit extreme features of these rules because of the same properties that produce their narrow gaps. Consequently these materials provide sensitive tests of theory, and
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Impurities and Defects
Investigating impurities and defects for any semiconductor material is an important topic. Much research has been devoted to impurity and defect states in wide-gap semiconductor materials. For the pseudobinary semiconductor alloy HgCdTe (mercury cadmium tellurium (MCT)), which is a good material for preparing infrared detectors, the investigation of its defects has a special significance. The behavior of impurities and defects in HgCdTe has been discussed in many papers in recent years. However, the research on impurities and defects of HgCdTe has encountered considerably more complexity and difficulty than that encountered in other semiconductors because of its narrow band gap, the low conduction band effective mass, the ease with which Hg vacancies are formed, and complex with other native point defects and impurities. Despite these difficulties, research in recent years have provided a basic description of impurities and defects, and their diffusion and photoelectric behavior in HgCdTe. For the narrow gap semiconductor material HgCdTe, we need to know which kind of impurities and defects exist in the material, their chemical composition and electrical activity, if they are p-type or n-type, the magnitude of the impurity concentration, the ionization energies of these defects, their impact on electrical and optical properties, how to experimentally observe their properties, and how to theoretically analyze their properties.
2.1 Conductivity and Ionization Energies of Impurities and Native Point Defects 2.1.1 Defects One of the major differences between real crystals and ideal crystals is that, in a real crystal, there are many defective areas where the regular arrangement of atoms has been destroyed. Defects result from many factors such as impurity atoms, growth aberrations, e.g., dislocations or planar defects, point defects resulting in an excess or a deficiency of some elements in the compound. The primary defects in an HgCdTe (Swink and Brau 1970; Yu 1976; Bye 1979; Mirsky and Shechtman 1980; J. Chu and A. Sher, Device Physics of Narrow Gap Semiconductors, Microdevices, c Springer Science+Business Media, LLC 2010 DOI 10.1007/978-1-4419-1040-0 2,
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2 Impurities and Defects
Wang et al. 1984; Cheung 1985; Cole et al. 1985; Bubulac et al. 1985; Cai 1986; Kurilo and Kuchma 1982; Datsenko et al. 1985; Rosemeier 1983; Petrov and Gareeva 1988; Schaake 1988; Yu et al. 1990; Chen 1990; Dean et al. 1991; Shin et al. 1991; Wang et al. 1992; Yang 1988) mainly derive from (1) intrinsic point defects, e.g., vacancies, interstitial atoms, antisites, and complexes of these defects; (2) impurities; (3) multidimensional structural defects, such as dislocation, grain boundaries, and strains. Thus the geometry of lattice defects includes point, line, planar and bulk defects. Because of a Maxwell distribution of atomic kinetic energies during crystal growth, some atoms always have a sufficient kinetic energy to leave lattice sites and be excited into “interstitial” positions to create a “vacancy–
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