An elastic model for the In-In correlations in In(x)Ga(1-x)As semiconductor alloys

Deviations from randomicity in In(x)Ga(1-x) As semiconductor alloys induced by elastic effects are investigated within the Keating potential. Our model is based on Monte Carlo simulations on large (4096 atoms) supercells, performed with two types of boundary conditions: Fully periodic boundary conditions represent the bulk, while periodic boundary conditions along the x and y directions and a free surface in the z direction simulate the epitaxial growth environment. We show that In-In correlations identified in the bulk tend to be enhanced in the epitaxially grown samples.Comment: 13 pages, 1 figure, published in Solid State Communication

Electric Field Control of Shallow Donor Impurities in Silicon

We present a tight-binding study of donor impurities in Si, demonstrating the adequacy of this approach for this problem by comparison with effective mass theory and experimental results. We consider the response of the system to an applied electric field: donors near a barrier material and in the presence of an uniform electric field may undergo two different ionization regimes according to the distance of the impurity to the Si/barrier interface. We show that for impurities ~ 5 nm below the barrier, adiabatic ionization is possible within switching times of the order of one picosecond, while for impurities ~ 10 nm or more below the barrier, no adiabatic ionization may be carried out by an external uniform electric field. Our results are discussed in connection with proposed Si:P quantum computer architectures.Comment: 18 pages, 6 figures, submitted to PR

Carbon antisite clusters in SiC: a possible pathway to the D_{II} center

The photoluminescence center D_{II} is a persistent intrinsic defect which is common in all SiC polytypes. Its fingerprints are the characteristic phonon replicas in luminescence spectra. We perform ab-initio calculations of vibrational spectra for various defect complexes and find that carbon antisite clusters exhibit vibrational modes in the frequency range of the D_{II} spectrum. The clusters possess very high binding energies which guarantee their thermal stability--a known feature of the D_{II} center. The di-carbon antisite (C_{2})_{Si} (two carbon atoms sharing a silicon site) is an important building block of these clusters.Comment: RevTeX 4, 6 pages, 3 figures Changes in version 2: Section headings, footnote included in text, vibrational data now given for neutral split-interstitial, extended discussion of the [(C_2)_Si]_2 defect incl. figure Changes version 3: Correction of binding energy for 3rd and 4th carbon atom at antisite; correction of typo

Tight-binding study of the influence of the strain on the electronic properties of InAs/GaAs quantum dots

We present an atomistic investigation of the influence of strain on the electronic properties of quantum dots (QD's) within the empirical $s p^{3} s^{*}$ tight-binding (ETB) model with interactions up to 2nd nearest neighbors and spin-orbit coupling. Results for the model system of capped pyramid-shaped InAs QD's in GaAs, with supercells containing $10^{5}$ atoms are presented and compared with previous empirical pseudopotential results. The good agreement shows that ETB is a reliable alternative for an atomistic treatment. The strain is incorporated through the atomistic valence force field model. The ETB treatment allows for the effects of bond length and bond angle deviations from the ideal InAs and GaAs zincblende structure to be selectively removed from the electronic-structure calculation, giving quantitative information on the importance of strain effects on the bound state energies and on the physical origin of the spatial elongation of the wave functions. Effects of dot-dot coupling have also been examined to determine the relative weight of both strain field and wave function overlap.Comment: 22 pages, 7 figures, submitted to Phys. Rev. B (in press) In the latest version, added Figs. 3 and 4, modified Fig. 5, Tables I and II,.and added new reference

Electric-Field Effects on the Band-Edge States of GaAs/AlAs Coupled Quantum Wells

“Judge Alexander R. Tiffany, its author, put out the first edition of this work in 1849. In the years 1851, 1858 and 1866, he put out the second, third and fourth editions, respectively. The fifth edition was published in 1873 with Judge Andrew Howell as its editor and he edited the succeeding editions to the ninth inclusive …. “The editorship of the present edition has been undertaken at the request of the family of Judge Tiffany, and while the editor is persuaded that better can be done, yet it is hoped that the present edition may share the favor so long shown to this work by the bench and bar of Michigan… “The citations of cases have been brought down to the 100th Northwestern Reporter and to the 132nd Michigan Reports. The Reporter citations are added for all cases since the beginning of the Reporter system. “Citations to statutes are to the Compiled Laws of 1897 and to the Session Laws of 1899, 1901 and 1903…”https://repository.law.umich.edu/books/1096/thumbnail.jp

Tight binding study of the influence of the strain on the electronic properties of InAs GaAs quantum dots

We presented an atomistic investigation of the influence of strain on the electronic properties of quantum dots QD s within the empirical sp3s tight binding ETB model with interactions up to second nearest neighbors and spin orbit coupling. Results for the model system of capped pyramid shaped InAs QD s in GaAs, with supercells containing 105 atoms are presented and compared with previous empirical pseudopotential results. The good agreement shows that the ETB is a reliable alternative for an atomistic treatment. The strain is incorporated through the atomic valence force field model. The ETB treatment allows for the effects of bond length and bond angle deviations from the ideal InAs and GaAs zinc blende structure to be selectively removed from the electronic structure calculation, giving quantitative information on the importance of strain effects on the bound state energies and on the physical origin of the spatial elongation of the wave function. Effects of dot dot coupling have also been examined to determine the relative weight of both strain field and wavefunction overla

Exciton distribution on single-walled carbon nanotube

In this paper we calculate the binding energy of an exciton using the tight-binding model and discuss the exciton distribution in detail. We analytically explain the dependence of the distribution direction of exciton on the chiral angle, and the distribution localization along the tube axis and oscillating along the tube circumference. The size of exciton is estimated to be slightly larger than the diameter of the nanotube and it shows two family patterns versus the inverse of tube diameter as similar as in the exciton binding energy