Tight binding theory of semiconductors

An extension of Harrison's theory of the two-center bond to the multicenter bond is applied to Zn3P2 and elemental boron. The theory predicts experimentally measurable properties with essentially the same accuracy as Harrison's theory predicts properties of tetrahedrally coordinated semiconductors. The second chapter uses the experimental elastic constants as a vehicle to test various aspects of Harrison's theory. It is found that the two central premises of the theory, the universal matrix elements and the Bond Orbital Approximation, are both remarkably good approximations to more elaborate theories. Harrison's repulsive interaction V sub 0 that stabilizes the crystal at its equilibrium spacing was found to be missing a significant contribution, one arising from the orthogonalization of valence wave functions to neighboring cores. The contribution is of sufficient magnitude to account for the rather severe underestimate of the bulk modulus. In the third chapter, tight-binding theory is used as a framework to calculate the configuration dependence of the Coulomb electron-electron interaction in pseudobinary alloys of semiconductors of the form A(0.5)B(0.5)C. It is found that there is a considerable configuration dependence of this interaction: random configurations have a higher internal energy than ordered ones. The Coulomb contribution to the mixing enthalpy is discussed, and is observed to be comparable to the strain contribution customarily considered.