Valence (chemistry)

About: Valence (chemistry) is a research topic. Over the lifetime, 24937 publications have been published within this topic receiving 645252 citations. The topic is also known as: valency.

Electronic bands of III-V semiconductor polytypes and their alignment

Abstract: The quasiparticle band structures of four polytypes 3C, 6H, 4H, and 2H of GaP, GaAs, GaSb, InP, InAs, and InSb are computed with high accuracy including spin-orbit interaction applying a recently developed approximate calculation scheme, the LDA-1/2 method. The results are used to derive band offsets $\ensuremath{\Delta}{E}_{c}$ and $\ensuremath{\Delta}{E}_{v}$ for the conduction and valence bands between two polytypes. The alignment of the band structures is based on the branch-point energy ${E}_{\mathrm{BP}}$ for each polytype. The aligned electronic structures are used to explain properties of heterocrystalline but homomaterial junctions. The gaps and offsets allow to discuss spectroscopic results obtained recently for such junctions in III-V nanowires.

Bonding, energies, and band offsets of Si-ZrO2 and HfO2 gate oxide interfaces.

Abstract: New oxides with high dielectric constant are required for gate oxides. ZrO2 is a typical example with ionic bonding. We give the rules for bonding at interfaces between Si and ionic oxides, to satisfy valence requirements and give an insulating interface. Total energies and band offsets are calculated for various (100)Si:ZrO(2) and HfO2 interface structures. The oxygen-terminated interface is found to be favored for devices, because it has no gap states and has a band offset which is rather independent of interfacial bonding.

Band structure of carbonated amorphous silicon studied by optical, photoelectron, and x-ray spectroscopy

Abstract: Hydrogenated silicon-carbon films prepared by glow discharge from silane-methane mixtures at low power density are used as a model system for the analysis of optical properties and band structure of amorphous tetrahedral semiconductors. Between 0 and 20 at. % of carbon in the solid, the optical gap and the static refractive index can be varied over a wide range without changing the chemical structure of the solid and its good semiconducting properties. The optical constants are well described by a simple two-band model of optical transitions, and the information on the band structure in the solid is condensed into one parameter, the average gap ${E}_{M}$, which corresponds to the energy difference between the centers of gravity of the valence and conduction bands. This value is very close to the energy spacing of the maxima in the distributions of the conduction and valence band deduced from soft-x-ray spectra, and exhibits a similar increase with carbon content. Beyond a carbon concentration of about 20 at. %, we observe a change in the nature of the material. The average gap ${E}_{M}$ increases much more rapidly than the optical gap; x-ray photoelectron spectroscopy indicates an incorporation of carbon in the form of Si-C-Si units in a tetrahedral network, whereas for concentrations smaller than 20 at. % the carbon is mainly incorporated as methyl groups ${\mathrm{CH}}_{3}$.

The band-gap excitons in gallium selenide

Abstract: Absorption, and reflexion spectra of GaSe near the fundamental gap are interpreted in terms of pseudopotential band calculations. Selection rules for the direct optical valence-to-conduction band transitions are derived. Valence band mixing induced by spin-orbit coupling is invoked to explain the low observed probability for transitions in light polarized perpendicular to the crystal c-axis. The spectra of the excitons associated with the direct gap are discussed in the ellipsoidal effectivemass approximation. Corrective terms are added to account for the observed exchange splitting of the exciton ground state. Field-free spectra as well as spectra modified by the presence of magnetic fields parallel and perpendicular to c are considered. The magneto-Stark effect which gives rise to a mixing of the 2s and2py states and thus renders the2py state visible affords determination of the anisotropy parameter. The value of this parameter as well as those of the components parallel and perpendicular to c of the reduced effective masses show that the electronic states in GaSe are nearly isotropic. This is in good agreement with the results of the pseudopotential band calculations which clearly demonstrate the three-dimensional character of valence and conduction bands.