452 research outputs found
Floating bonds and gap states in a-Si and a-Si:H from first principles calculations
We study in detail by means of ab-initio pseudopotential calculations the
electronic structure of five-fold coordinated (T_5) defects in a-Si and a-Si:H,
also during their formation and their evolution upon hydrogenation. The
atom-projected densities of states (DOS) and an accurate analysis of the
valence charge distribution clearly indicate the fundamental contribution of
T_5 defects in originating gap states through their nearest neighbors. The
interaction with hydrogen can reduce the DOS in the gap annihilating T_5
defects.Comment: To appear in Europhysics Let
Indented Barrier Resonant Tunneling Rectifiers
This article concerns a novel negative-conductance device consisting of a series of N laterally indented barriers which exhibits resonant tunneling under one bias polarity and simple tunneling under the opposite one, thus acting as a rectifier. Electrons undergo resonant tunneling when the bias creates a band profile with N triangular wells which can each contain a resonant state. From 1 to N the addition of each indentation can be used to increase the current density and the rectification ratio, calculated at the current-peak bias at resonance, provided that at a given bias all the states in the triangular wells align each other with the emitter Fermi energy in order to form a resonance along the structure. © 1996 American Institute of Physics.80741744176Chang, L.L., Esaki, L., Tsu, R., (1974) Appl. Phys. Lett., 24, p. 593Sollner, T.C.L.G., Goodhue, W.D., Tannenwald, P.E., Parker, C.D., Peck, D.D., (1983) Appl. Phys. Lett., 43, p. 588Sollner, T.C.L.G., Tannenwald, P.E., Goodhue, W.D., Peck, D.D., (1984) Appl. Phys. Lett., 45, p. 1319Ricco, B., Azbel, M.Ya., (1984) Phys. Rev. B, 29, p. 1970Pötz, W., (1989) J. Appl. Phys., 66, p. 2458Frensley, W.R., (1990) Rev. Mod. Phys., 62, p. 745Chevoir, F., Vinter, B., (1993) Phys. Rev. B, 47, p. 7260Chang, L.L., Mendez, E.E., Tejedor, C., (1991) Resonant Tunneling in Semiconductors: Physics and Applications, , Plenum, New YorkSollner, T.C.L.G., Brown, E.R., Goodhue, W.C., Microwave and Milimeter-Wave Resonant Tunneling Diodes (1987) Picosecond Electronics and Optoelectronics Technical Digest, 87 (1), pp. 143-145. , Optical Society of America, Washington, D.CLiu, H.C., Coon, D.D., (1987) Appl. Phys. Lett., 50, p. 1669Schulz, P.A., Da Silva, G., (1988) Appl. Phys. Lett., 52, p. 960Papp, G., Di Ventra, M., Coluzza, C., Baldereschi, A., Margaritondo, G., (1995) Superlattices Microstruct., 17, p. 273Di Ventra, M., Papp, G., Coluzza, C., Baldereschi, A., (1994) Proceedings of the 22nd International Conference on the Physics of Semiconductors, p. 1600. , edited by D. J. Lockwood World Scientific, SingaporeVassel, M.O., Lee, J., Lockwood, H.F., (1983) J. Appl. Phys., 54, p. 5206Papp, C., Coluzza, C., Di Ventra, M., Baldereschi, A., Margaritondo, G., Gu, B.-Y., (1995) Superlattices Microstruct., 17, p. 117Adachi, S., (1985) J. Appl. Phys., 58, pp. R1Rossmanith, M., Syassen, K., Böckenhoff, E., Ploog, K., Von Klitzing, K., (1991) Phys. Rev. B, 44, p. 3168Ohno, H., Mendez, E.E., Wang, W.I., (1990) Appl. Phys. Lett., 56, p. 1793Guéret, P., Rossel, C., Marclay, E., Meier, H., (1989) J. Appl. Phys., 66, p. 278Guéret, P., Rossel, C., Schulp, W., Meier, H., (1989) J. Appl. Phys., 66, p. 431
Effective Hamiltonian for Ga_{1-x}Mn_xAs in the Dilute Limit
We derive an effective Hamiltonian for in
the dilute limit, where can be described in
terms of spin polarons hopping between the {\rm Mn} sites and coupled
to the local {\rm Mn} spins. We determine the parameters of our model from
microscopic calculations. Our approach treats the large Coulomb interaction in
a non-perturbative way, captures the effects of spin-orbit coupling and
disorder, and is appropriate for other p-doped magnetic semiconductors. Our
model applies to uncompensated {\rm Mn} concentrations up to .Comment: 4 pages, 4 figures, Version to appear in Phys. Rev. Let
Multiband theory of quantum-dot quantum wells: Dark excitons, bright excitons, and charge separation in heteronanostructures
Electron, hole, and exciton states of multishell CdS/HgS/CdS quantum-dot
quantum well nanocrystals are determined by use of a multiband theory that
includes valence-band mixing, modeled with a 6-band Luttinger-Kohn Hamiltonian,
and nonparabolicity of the conduction band. The multiband theory correctly
describes the recently observed dark-exciton ground state and the lowest,
optically active, bright-exciton states. Charge separation in pair states is
identified. Previous single-band theories could not describe these states or
account for charge separation.Comment: 10 pages of ReVTex, 6 ps figures, submitted to Phys. Rev.
Dynamical-charge neutrality at a crystal surface
For both molecules and periodic solids, the ionic dynamical charge tensors
which govern the infrared activity are known to obey a dynamical neutrality
condition. This condition enforces their sum to vanish (over the whole finite
system, or over the crystal cell, respectively). We extend this sum rule to the
non trivial case of the surface of a semiinfinite solid and show that, in the
case of a polar surface of an insulator, the surface ions cannot have the same
dynamical charges as in the bulk. The sum rule is demonstrated through
calculations for the Si-terminated SiC(001) surface.Comment: 4 pages, latex file, 1 postscript figure automatically include
Coupling of electron rotation with spin in semiconductors
Account of an intrinsic spin-orbit coupling in the valence bands of common
semiconductors yields the scalar spin-orbit-rotation term in the effective-mass
Hamiltonian of the conduction-band electron. This result is obtained within the
multiband envelope function approximation. Fundamentally, the
spin-orbit-rotation coupling can be described in purely geometric terms as a
consequence of the difference in the Berry phase acquired by the components of
the spin-orbitally mixed Kramers-doublet during its cyclic evolution in the
reciprocal momentum space.Comment: Will appear in Phys. Lett.
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