Luminescent Amorphous Silicon Layers

1997 ◽  
Vol 486 ◽  
Author(s):  
G. Allan ◽  
C. Delerue ◽  
M. Lannoo
Keyword(s):  
Electronic Structure ◽  
Amorphous Silicon ◽  
Radiative Recombination ◽  
Crystalline Silicon ◽  
Tight Binding ◽  
Blue Shift ◽  
Localized States ◽  
Structure Model ◽  
Radiative Recombination Rate ◽  
Tight Binding Approximation

AbstractThe electronic structure of amorphous silicon layers has been calculated within the empirical tight binding approximation using the Wooten-Winer-Weaire atomic structure model. We predict an important blue shift due to the confinement for layer thickness below 3 nm and we compare with crystalline silicon layers. The radiative recombination rate is enhanced by the disorder and the confinement but remains quite small. The comparison of our results with experimental results shows that the density of defects and localized states in the studied samples must be quite small.

Electronic Structure of Amorphous Silicon

1997 ◽  
Vol 491 ◽  
Author(s):  
G. Allan ◽  
C. Delerue ◽  
M. Lannoo
Keyword(s):  
Electronic Structure ◽  
Amorphous Silicon ◽  
Tight Binding ◽  
Localized States ◽  
Band Offset ◽  
Valence Band Offset ◽  
Tight Binding Approximation ◽  
Exponential Tails ◽  
Si Model ◽  
Hydrogenated Amorphous

ABSTRACTThe electronic structure of a continuous network model of tetrahedrally bonded amorphous silicon (a-Si) and of a model hydrogenated amorphous silicon (a-Si:H) that we have built from the a-Si model are calculated in the tight binding approximation. The band edges near the gap are characterized by exponential tails of localized states induced mainly by the variations in bond angles. The spatial localization of the states is compared between a-Si and a-Si:H. Valence band offset between the amorphous and the crystalline phases is calculated.

Local Electronic Structure and Short-Range Order in a Computer Simulated Amorphous Metal

1991 ◽  
Vol 02 (01) ◽  
pp. 232-237 ◽  
Author(s):  
A.Ya. BELENKII ◽  
M.A. FRADKIN
Keyword(s):  
Electronic Structure ◽  
Short Range ◽  
Short Range Order ◽  
Local Density ◽  
Tight Binding ◽  
Amorphous Metal ◽  
Range Order ◽  
Tight Binding Approximation ◽  
Electronic Parameters ◽  
Local Electronic Structure

The relationship between topological short-range order and a local electronic structure was analyzed in the computer model of an amorphous metal. The model, obtained by means of the original self-consistent cluster simulation procedure was studied with the use of Voronoi tesselation, the distribution of the atomic level stresses and the icosahedral order parameters. It was found that a marked correlation exists within 2 atomic parameter groups, one of which corresponds to the local dilatation and the other to the spherical symmetry distortion. The local density of electronic d-states (DOS) and the distribution of the electronic parameters was analyzed. The local electronic structure, calculated within the tight-binding approximation, appears to depend on the local atomic order by two-fold means: the interatomic distances decrease leads to the increase of the local bandwidth, and the icosahedral configuration distortion reduces the DOS at the Fermi level. The study of the local configurations stability shows, that the most stable configurations are the slightly distorted icosahedra.

SIMPLE QUANTUM CONFINEMENT THEORY FOR EXCITON IN INDIRECT GAP NANOSTRUCTURES

2000 ◽  
Vol 14 (15) ◽  
pp. 1559-1566 ◽  
Author(s):  
NGUYEN THI VAN OANH ◽  
NGUYEN AI VIET
Keyword(s):  
Optical Properties ◽  
Simple Model ◽  
Quantum Confinement ◽  
Tight Binding ◽  
Blue Shift ◽  
Analytic Solutions ◽  
Silicon Nanostructures ◽  
Tight Binding Approximation ◽  
Mass Approximation ◽  
Simple Quantum

We propose in this work a simple quantum confinement theory for excitons based on the effective mass approximation, for investigation of optical properties of indirect gap nanostructures. We show that using this simple model, we can get the analytic solutions and reobtain the main tight-binding approximation numerical results of Hill et al.1 for silicon nanostructures: blue shift of band gap and increase overlap between the states at the band edges when the nanostructures size in decreased.

Theory of Pressure Effects on Silicon Nanocrystallites

1996 ◽  
Vol 452 ◽  
Author(s):  
G. Allan ◽  
C. Delerue ◽  
M. Lannoo
Keyword(s):  
Quantum Confinement ◽  
Radiative Recombination ◽  
Local Density ◽  
Tight Binding ◽  
Pressure Effects ◽  
Radiative Recombination Rate ◽  
Electron Hole ◽  
Silicon Nanocrystallites ◽  
Semi Empirical ◽  
Confinement Model

AbstractPressure effects on silicon nanocrystallites are calculated using semi-empirical tight-binding and ab-initio local density calculations. Using the confinement model in porous silicon a red shift of the luminescence energy with increasing pressure is obtained. Quantum confinement in BC8 phase silicon nanocrystallites obtained after release of high pressure are also studied. It increases the cluster gap and also enhances the electron-hole radiative recombination rate.

Electronic Structure of Si/InAs Composite Channels

2007 ◽  
Vol 995 ◽  
Author(s):  
Marta Prada ◽  
Neerav Kharche ◽  
Gerhard Klimeck
Keyword(s):  
Electronic Structure ◽  
Quantum Well ◽  
Effective Mass ◽  
Tight Binding ◽  
Localized States ◽  
Equivalent Thickness ◽  
Binding Model ◽  
Direct Bandgap ◽  
Effective Masses ◽  
Composite Channels

AbstractElectronic structure calculations on composite channels, consisting of indium arsenide grown on the technologically relevant (001), (011) and (112)-orientated silicon surfaces are reported. The calculations are performed with NEMO 3-D, where atoms are represented explicitly in the sp3d5s* tight-binding model. The Valence Force Field (VFF) method is employed to minimize the strain. NEMO 3-D enables the calculation of localized states in the quantum well (QW) and their dispersion in the quantum well plane. From this dispersion, the bandgap, its direct or indirect in character, and the associated effective masses of the valence and conduction band can be determined. Such composite bandstructure calculations are demonstrated here for the first time. The numerical results presented here can then be included in empirical device models to estimate device performance. Pure InAs QWs create a direct bandgap material, with a relatively small gap and effective masses of about one order of magnitude smaller than for pure Si QW of equivalent thickness. Si, on the other hand, has a larger bandgap, superior thermal and mechanical properties, and a heavily invested industry. Thus heteroepitaxy of both components is expected to yield a highly optimized overall system. For samples grown along the (001) direction, Si is a direct bandgap material, and deposition of an InAs 3nm layer reduces substantially the hole effective mass and slightly the electronic mass, decreasing the magnitude of the gap. Along the (011) and (112)-growth direction, Si QWs are indirect bandgap material, and deposition of a few InAs layers suffies to make the new material a direct-bandgap heterostructure, decreasing significantly the electronic effective mass. (011) and (112) are the experimentally most relevant growth directions since they prevent heterointerface dipoles.

Electronic Structure of CBN Ball Within Tight-Binding Approximation

1992 ◽  
Vol 9 (11) ◽  
pp. 581-584 ◽  
Author(s):  
Liu Jingnan ◽  
Huang Mingwei ◽  
Gu Binglin
Keyword(s):  
Electronic Structure ◽  
Tight Binding ◽  
Tight Binding Approximation

Orbitals and bands at metal surfaces: photoemission from the {110} surface of tungsten

1981 ◽  
Vol 376 (1767) ◽  
pp. 565-583 ◽  
Keyword(s):  
Electronic Structure ◽  
Band Structure ◽  
Surface State ◽  
Photon Emission ◽  
Tight Binding ◽  
Tight Binding Approximation ◽  
The Third ◽  
Surface Brillouin Zone ◽  
Orbital Character ◽  
Bulk Band

The electronic structure of the {110} surface of tungsten has been investigated by using angle-resolved photoemission. A surface state has been identified and characterized throughout the surface Brillouin zone (s. B. z.). Its dispersion is found to correlate with the projected band gap between the third and fourth bands of the tungsten bulk band structure. It is identified by comparison with Inglesfield’s calculation as having predominantly m = 1 d-orbital character. With photon energies of 21.2 and 40.8 eV, intense photoemission from the surface state is only observed after surface Umklapp, whereas, with 16.8 eV, photon emission is observed in both the first and second s. B. zs. The applicability of the tight-binding approximation to the elucidation of the electronic structure of a metal surface is examined with particular reference to this surface state. A qualitative analysis of the observed photoemission intensities is consistent with emission from a tungsten e g orbital that is hybridized with e g orbitals on neighbouring atoms.

Structural Relaxation of Vacancies in Amorphous Silicon

1997 ◽  
Vol 467 ◽  
Author(s):  
Eunja Kim ◽  
Young Hee Lee ◽  
Changfeng Chen ◽  
Tao Pang
Keyword(s):  
Amorphous Silicon ◽  
Structural Relaxation ◽  
Crystalline Silicon ◽  
Defect Density ◽  
Tight Binding ◽  
Unusual Behavior ◽  
High Defect Density ◽  
Significant Difference ◽  
Gap States ◽  
Dynamics Method

ABSTRACTWe have studied the structural relaxation of vacancies in amorphous silicon (a-Si) using a tight-binding molecular-dynamics method. The most significant difference between vacancies in a-Si and those in crystalline silicon (c-Si) is that the deep gap states do not show up in a-Si. This difference is explained through the unusual behavior of the structural relaxation near the vacancies in a-Si, which enhances the sp2 + p bonding near the band edges. We have also observed that the vacancies do not migrate below 450 K although some of them can still be annihilated, particularly at high defect density due to large structural relaxation.

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