Papers by Keyword: GW Calculations

Abstract: Recently, polytypism has been observed in nanowires in materials, for which normally only one crystal structure is stable. For example, GaAs, nanowires can have wurtzite or mixed zincblende/wurtzite. Here we provide band structure parameters for wurzite and 4H GaAs and use them for modeling the nanowire electronic states. The band gap, crystal field splitting, and its strain dependence, as well as the effective mass parameters are calculated using the quasiparticle self-consistent GW method. The nanowire electronic states are obtained in the envelope function approximation within a simplified cylindrical model. The crystal field splitting of the wurtzite GaAs valence band is found to be 180 meV while in 4H-GaAs it is less than half 69 meV, suggesting a downward bowing as function of hexagonality. The conduction band minimum at Γ changes symmetry character under strain. We discuss the consequences for nanowires and determine the conditions under which a polarization reversal of photoluminescence can occur from mostly perpendicular to parallel to the wire.

Abstract: First-principles calculations are presented for CdGeN2 and ZnGe0.5Sn0.5N2 compounds with the orthorhombic structure derived from wurtzite. Lattice constants and internal parameters are obtained from local density approximation full-potential linearized muffin-tin orbital calculations and the quasiparticle self-consistent GW method is used to calculate the band structures. Corrections for zero-point motion and exciton binding energy are included. Both approaches lead to gaps in the blue-green region.

Abstract: Single Crystalline Langatate (La₃Ta_0.5Ga_5.5O₁₄, LTG) Has Been Widely Used in Piezoelectric Sensors for High Temperature Applications because of its Structural Stability at High Temperature. however, in the Recent Experiment, an Increase of Electrical Conductivity Has Been Also Observed at the Intermediate Temperature Region Ranges from 300 to 700°C. Also, in Theoretical Calculations, Penta-Valent Ta Vacancy Can Be Easily Generated and Influence Resistivity Degradation of the Crystal. In this Study, to Elucidate the Ta Vacancy Effects on Electrical Conductivity of LTG and Recently Proposed Ba-Based P321 Crystal such as BTGS and BTAS, Electrical Conductivity of those Materials Were Calculated and Compared by Utilizing Boltzmann Transport Theory. The Calculated GW Band Gaps of Perfect BTGS and BTAS (5.94 Ev and 6.69 Ev, Respectivily) Were much Larger than that of LTG (5.36 Ev). Also, at Intermediate Temperature (1000K), the Calculated Electrical Conductivity of LTG with V'''''Ta (in Kröger-Vink Notation [13]) Was around Twelve Times Higher than the Conductivity of BTGS and BTAS with Ta Vacancy.