Electronic band-edge structure, effective masses, and optical absorption of Si1-xGex using an extended FPLAPW/VCA/LDA+U computational method

Abstract

Electronic band-edge structure and optical properties of Si1-xGex are investigated theoretically emloying a full-potential linearized augmented plane wave (FPLAPW) method. The exchange-correlation potential in the local density approximation (LDA) is corrected by an on-site Coulomb potential (i.e., within the LDA+USIC approach) acting asymmetrically on the atomic-like orbitals in the muffin-tin spheres. The electronic structure of the Si1-xGex is calculated self-consistently, assuming a Td symmetrized Hamiltonian and a linear behavior of the valence-band eigenfunctions for Si, SiGe, and Ge with respect to Ge composition x, assuming randomly alloyed crystal structure. i.e., a "virtual-crystal like" approximation (VCA). We show that this approach yields accurate band-gap energies, effective masses, dielectric function, and optical properties of Si1-xGex. We perform absorption measurements showing the band-gap energy for x < 0.25.