1,878,321 research outputs found
Giant birefringence in zinc-blende-based artificial semiconductors
No full textWe use extended-basis empirical tight-binding calculations and examine the anisotropy of the refractive index in ultrashort-period superlattices of materials sharing no common atom. We find that a strong birefringence can be engineered in these articial semiconductors, allowing phase matching for frequency difference generation. The prominent role of epitaxial constraint and bond-length alternation is evidenced
Atomistic spin-orbit coupling and k center dot p parameters in III-V semiconductors
No full textThe most accurate description of spin splittings in semiconductor nanostructures has been obtained from a 14-band k center dot p model, but the historical way in which it has developed from the 8-band Kane model has endorsed somewhat arbitrary values of the momentum and spin-orbit matrix elements. We have systematically determined the 14-band k center dot p parameters for III-V semiconductors from a 40-band tight-binding model. Significant changes with respect to previously accepted values were found even for GaAs. For all materials investigated, the resulting Dresselhaus spin-orbit coupling parameter is in good agreement with experimental values. The atomistic background of the present parametrization allows new insight into the spin-orbit coupling Delta(-) between bonding and antibonding orbitals and its dependence on ionicity
Full-band tunneling in high-kappa oxide MOS structures
No full textIn this paper, we investigate the tunneling properties of ZrO2 and HfO2 high-kappa oxides, by applying quantum mechanical methods that include the full-band structure of Si and oxide materials. Semiempirical sp(3)s*d tight-binding parameters have been determined to reproduce ab-initio band dispersions. Transmission coefficients and tunneling currents have been calculated for Si/ZrO2/Si and Si/HfO2/Si MOS structures, showing a very low gate leakage current in comparison to SiO2-based structures with the same equivalent oxide thickness. The complex band structures of ZrO2 and HfO2 have been calculated and used to develop an energy-dependent effective tunneling mass model. We show that effective mass calculations based on this model yield tunneling currents in close agreement with full-band results
Giant spin splittings in GaSb/AlSb L-valley quantum wells
No full textFor GaSb/AlSb heterostructures with the absolute conduction minimum deriving from the L point of the bulk Brillouin zone, we predict zero-field spin splittings well exceeding 10 meV, about one order of magnitude larger than typical values resulting from the Dresselhaus and Rashba spin-orbit coupling terms near the zone center. Electronic structure calculations are performed within an improved tight-binding model and the main results can be reproduced in a 4x4 k.p Hamiltonian including band parameters and k-linear spin splittings derived from the GaSb bulk. Our results provide direct insight into L-valley heterostructures, indicating a promising direction for future research on spintronics
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