NONPARAMETRIZED TIGHT-BINDING METHOD FOR LOCAL AND EXTENDED DEFECTS IN HOMOPOLAR SEMICONDUCTORS

A general nonparametrized tight-binding method for the calculation of the electronic structure of defects in infinite and semi-infinite homopolar semiconductor crystals is presented. Atomic orbitals are used as the basis set. The electronic charge densities, charge distributions, occupation numbers, etc. are calculated by means of the appropriate Green's-function matrix elements between the atomic orbitals. The Hamiltonian matrix elements involved in the calculations are obtained from complete Hartree-Fock calculations in finite clusters of atoms with the same chemical environment as that of the considered defects. The correct treatment of the nonorthogonal basis set is found to be essential, and it is performed by means of the concept of dual basis. As a test of the method, bulk silicon is studied, and possible improvements of the approximations made are explored. Interstitial oxygen and the substitutional complex B-H in bulk silicon, arsenic-passivated (111)-1 x 1, and (100)-2 x 1 silicon surfaces, and a Si-H complex replacing an arsenic atom in the Si(111)-1 x 1:As surface are all analyzed in detail. Spin-polarization possibilities are explored and used to analyze the Si(100)-2 x 1 reconstructed surface and the substitution of an As atom by a Si atom in the previously studied Si(111)-1 x 1: As passivated surface.