Reversible Modulation of Spontaneous Emission by Strain in Silicon Nanowires

We computationally study the effect of uniaxial strain in modulating the spontaneous emission of photons in silicon nanowires. Our main finding is that a one to two orders of magnitude change in spontaneous emission time occurs due to two distinct mechanisms: (A) Change in wave function symmetry, where within the direct bandgap regime, strain changes the symmetry of wave functions, which in turn leads to a large change of optical dipole matrix element. (B) Direct to indirect bandgap transition which makes the spontaneous photon emission to be of a slow second order process mediated by phonons. This feature uniquely occurs in silicon nanowires while in bulk silicon there is no change of optical properties under any reasonable amount of strain. These results promise new applications of silicon nanowires as optoelectronic devices including a mechanism for lasing. Our results are verifiable using existing experimental techniques of applying strain to nanowires

Giant birefringence in zinc-blende-based artificial semiconductors

We 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

The 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

Giant spin splittings in GaSb/AlSb L-valley quantum wells

For 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

Tunneling properties of MOS systems based on high-k oxides

In this work, we show full-band calculations of the tunneling properties of ZrO2 and HfO2 high-kappa oxides. First, we have determined serniernpirical sp(3)s*d tight-binding (TB) parameters which reproduce ab-initio band dispersions of the high-kappa oxides; then we have calculated transmission coefficients and tunneling currents for Si/ZrO2/Si and Si/HfO2/Si MOS structures. Results show 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; based on them we develop an energy dependent effective tunneling mass model. It is shown that this model can be used to obtain effective mass tunneling currents close to full band results

Tunneling properties of MOS systems based on high-k oxides

In this work, we show full-band calculations of the tunneling properties of ZrO2 and HfO2 high-kappa oxides. First, we have determined serniernpirical sp(3)s*d tight-binding (TB) parameters which reproduce ab-initio band dispersions of the high-kappa oxides; then we have calculated transmission coefficients and tunneling currents for Si/ZrO2/Si and Si/HfO2/Si MOS structures. Results show 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; based on them we develop an energy dependent effective tunneling mass model. It is shown that this model can be used to obtain effective mass tunneling currents close to full band results