Semiconductors interatomic interaction

The magnitude of the nonlinearity in this case is determined by the absorption coefficient of the semiconductor, a0, as well as the electron effective mass, me. The effective mass is determined by the transfer (or resonance) integral between atoms or molecules in the framework of the Hiickel model [15]. Stronger interatomic interaction gives a larger transfer integral, smaller effective mass, and steeper curvature in the energy band... 

INTERATOMIC INTERACTION OF IMPURITIES IN HEAVILY DOPED SEMICONDUCTORS ... 

Metropolis Monte Carlo (MC) simulations (Allen and Tildesley 1987 Frenkel and Smit 2002) have been used to predict the structural and thermodynamic properties of mixtures of elemental semiconductors as also compound semiconductors. MC simulations have been conducted using both the VFF and Tersoff potential models to describe the interatomic interactions. The structural properties determined include lattice constants, thermal expansion coefQdents and bond lengths. The temperature versus composition miscibility diagram of ternary alloys at a given pressure, and the miscibility envelope for quaternary alloys at given temperature and pressure conditions have been determined using the transition matrix Monte C arlo (TMMC) method. 

It is traditional for quantmn theory of molecular systems (molecular quantum chemistry) to describe the properties of a many-atom system on the grounds of interatomic interactions applying the hnear combination of atomic orbitals (LCAO) approximation in the electronic-structure calculations. The basis of the theory of the electronic structure of solids is the periodicity of the crystalline potential and Bloch-type one-electron states, in the majority of cases approximated by a linear combination of plane waves (LCPW). In a quantmn chemistry of solids the LCAO approach is extended to periodic systems and modified in such a way that the periodicity of the potential is correctly taken into account, but the language traditional for chemistry is used when the interatomic interaction is analyzed to explain the properties of the crystalhne sohds. At first, the quantum chemistry of solids was considered simply as the energy-band theory [2] or the theory of the chemical bond in tetrahedral semiconductors [3]. From the beginning of the 1970s the use of powerful computer codes has become a common practice in molecular quantum chemistry to predict many properties of molecules in the first-principles LCAO calculations. In the condensed-matter studies the accurate description of the system at an atomic scale was much less advanced [4]. 

Tab. 11.1. Tight-binding parameters obtained from the least-square-error fit to LMTO band dispersions for the nine ll-VI semiconductors in the sp d basis with the A-B and B-B interactions. The first row lists the interatomic spacings in A, the next eight rows contain the onsite energies for all the orbitals, e.g. the row for dc t2) lists the entries for the t2cl orbital onsite energies for the cation. The subscript a denotes the anion. The last fifteen rows list the Slater Koster parameters. The last column shows the average value of the Slater Koster parameters multiplied by the square of the cation-anion distance, d. ...

When temperature is lowered, the band gaps usually increase [15]. There again, a few materials like lead sulphides or some copper halides are exceptions with a band gap increasing with temperature [96]. A quantitative analysis of the temperature dependence of the energy gaps must consider the electron-phonon interaction, which is the predominant contribution, and the thermal expansion effect. The effect of thermal expansion can be understood intuitively on the basis of the decrease of the interatomic distances when the temperature is decreased. A quantitative analysis of the electron-phonon contributions is more difficult, and most calculations have been performed for direct band-gap structures [75], Multi-parameter calculations of the temperature dependence of band gaps in semiconductors can be found in [81],... 

The electrical properties of semiconductors depend on the perfection of the crystal structure and the nature of the impurities it contains. However, the decisive factor responsible for semiconductor properties is the short-range order. By this is meant the symmetry of the electron shells, the valence an es, the interatomic distances, etc., i.e., the nature of the forces of the chemical interaction between the atoms. This is indicated by the fact that the semiconducting properties of many crystalline semiconductors are retained after melting [1] and also by the existence of a large number of liquid, amorphous, and glassy semiconductors. 

Of all the physical characteristics of solids, the dynamical properties give a rather complete description of various aspects of the electronic ground state elasticity, phonon frequencies, dispersion, phase transformations, anharmonicity - they are all derived from the properties of interatomic bonds. Therefore it seems only natural to attempt to trace the origins of semiconductor dynamics back to the behavior of electrons, which ultimately reduces to electron - electron and electron - nuclei interactions. These are the starting point of "ab initio" theories. 

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