Effective mass-like states of the deep acceptor level of Au and Pt in silicon

In this note we report the absorption spectra associated with the acceptor level of Au and Pt in silicon. The structures observed are experimental evidence of effective mass-like states related with these centres. A symmetry lower than T_d is suggested for both centres.     

Resonant interaction of acceptor states and optical phonons in silicon

The resonance broadening of line 2 in the excitation spectrum of gallium acceptors in silicon due to near coincidence of its energy with that of the zone center optical phonons, $\text{h}\text{?}$ω₀, has been confirmed under significantly improved experimental conditions. An additional feature labeled X and line 2 are interpreted as mixed excitations of the bound-hole and the optical phonon. Under uniaxial stress, the stress induced components of line 2 which approach $\text{h}\text{?}$ω₀ become more phonon-like and get “pinned” while the components of X become bound-hole-like as they recede from $\text{h}\text{?}$ω₀, and exhibit a striking increase in intensity.     

Paramagnetic states in doped amorphous silicon and germanium

ESR-results for doped hydrogenated amorphous silicon and germanium are discussed. g-values and linewidths of the resonances as well as effective correlation energies of the corresponding energy states are compared for both materials. It is shown that the existing large differences of these quantities between a-Si : H and a-Ge : H can be explained by the differences of spin-orbit coupling and degree of localization.     

Correlation effects and the density of states in amorphous silicon

The evaluation of the density of gap states from the charge density measured in field-effect experiments is considered in terms of a model which incorporates electron correlation effects. Due to the positive Hubbard U a density of states is deduced which differs appreciably from the “field effect” densities published previously. Besides the lack of the E_x and E_y peaks the minimum density is found to be ～ 10¹⁵ ? 10¹⁶ cm^?3 eV^?1.     

The gold donor and acceptor level in p-type silicon

DLTS measurements on the gold donoe and acceptor level in p-type silicon and reported. From the experimental data it must be concluded that the gold donor and the acceptor level are caused by the same defect, that the acceptor level lying 0.546eV below the conduction band is temperature independently pinned to the conduction band and that the hole capture cross section of the acceptor level

_P^A is temperature independent in the measured range of 215 to 345 K.     

Photothermal detection of surface states in amorphous silicon films

A new method for the determination of surface states in amorphous silicon films is proposed. The method is based on the observation of enhancement of the interference fringe amplitude in photothermal deflection spectra, due to the presence of surface states.A theoretical approach is presented, together with the experimental results and an evaluation of the density of surface states. The method proves to be adequate, in most cases, to yield results in good agreement with those reported in literature.     

Density of phonon states in amorphous germanium and silicon

The density of phonon states in amorphous germanium and silicon is calculated by statistically averaging the crystalline phonon density of states according to the radial distribution function. A simple rigid ion model is used to calculate the density of phonon states at various lattice spacings. The appropriate model parameters are obtained from the pressure dependent elastic constants and the Raman frequency. The calculated results compare favorably to experimental data obtained by infrared and Raman scattering and the results of other theoretical calculations.     

Urbach edge and the density of states in hydrogenated amorphous silicon

Photoconductivity measurements of the optical absorption edge and time-of-flight measurements of the hole drift mobility, on the same amorphous silicon film, enable us to identify the origin of the Urbach edge in amorphous silicon with the density of states in the valence band tail.     

Evidence for an excited level of the neutral indium acceptor in silicon

On the basis of the dependence of the photoluminescence on pump power, indium concentration and temperature we have determined that an excited level of the neutral indium acceptor exists 4.1 ± 0.1 meV above the ground state.     

Effect of uniaxial stress on shallow acceptor states in silicon and germanium

Summary Energies and wave functions of shallow acceptor states under uniaxial stress have been computed in silicon and germanium. Calculations have been carried out up to high stress values within the effective-mass approximation. The full cubic crystal symmetry has been taken into account. The splittings of the ground state and of the odd-parity excited states, the relative intensities of optical transitions, as well as the energies of odd states for high stress values have been found to be in agreement with the results of optical measurements. However, results for even-parity excited states cannot as yet be compared with present experiments.

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Riassunto Le energie e le funzioni d'onda degli stati accettori poco prodondi sotto tensione uniassiale sono state calcolate per silicio e germanio. I calcoli sono stati fatti fino ad alti valori di tensione nell'approssimazione della massa efficace. è stata presa in considerazione la simmetria cubica completa del cristallo. Gli sdoppiamenti dello stato fondamentale, degli stati eccitati a parità dispari, le intensità relative delle transizioni ottiche, cosí come le energie degli stati dispari per alti valori di tensione sono in accordo con i risultati delle misurazioni ottiche. Tuttavia, i risultati per gli stati eccitati a parità pari non possono ancora essere confrontati con gli esperimenti attuali.

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Реэюме Вычисляются энергии и волновые функции мелких акцепторных состояний при одноосном напряжении в кремнии и германии. Вычисления проводятся в рамках приближения эффективной массы вплоть до больших значений напряжений. Учитывается полная кубическая симметрия кристалла. Получается, что расщепления основного состояния и нечетных возбужденных состояний, относительные интенсивности оптических переходов, а также энергии нечетных состояний при больших значениях напряжений согласуются с результатами оптических измерений. Однако, результаты для четных возбужденных состояний не могут быть еще сравнены с имеющимися экспериметами.

     

Density of states and charge distribution in hydrogenated amorphous silicon

The local density of states and the charge distribution in a cluster model of hydrogenated amorphous silicon is calculated using the recursion method. The results indicate an average charge transfer of 0.3 electrons from silicon to hydrogen. In addition Si-H dipoles carry small negative charges, which are neutralized by a positively charged bulk of silicon atoms. There are also static spatial charge fluctuations, which are due to the topological disorder.     

The density of states in the mobility gap of halogenated amorphous silicon

Summary The density of states in the mobility gap of halogenated amorphous silicon has been measured by the field effect technique. The results are discussed to shed light on the reality of a peak found in the DOS. A comparison is made with the DOS curves obtained by SCLC in the same material. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Experimental elucidation of hydrogen local density of states in hydrogenated amorphous silicon

Ultraviolet and X-ray photoemission spectroscopies (UPS and XPS) are used to study the valence band in device quality hydrogenated amorphous silicon films (s-Si:H). Their results are combined to obtain estimated information about the hydrogen local density of states (HLDOS). The monohydride bonding configuration and the occurence of interhydride bonding between H atoms are confirmed by the experimental data.     

Unraveling the symmetry of the hole states near the Fermi level in the MgB2 superconductor

We use x-ray absorption spectroscopy (XAS) and electron energy loss spectroscopy (EELS) to study the fine structure at the K edge of boron in MgB(2). We observe in XAS a peak of width 0.7 eV at the edge threshold, signaling a narrow energy region with empty boron p states near the Fermi level. The changes in the near edge structure observed in EELS with direction of the momentum transfer imply that these states have p(x)p(y) symmetry. Our observations are consistent with electronic structure calculations indicating a narrow energy window of empty p(x)p(y) states that falls to zero at 0.8 eV above the Fermi level. The disappearance of the p(x)p(y) feature in EELS at grain boundaries suggests that this signature may become powerful in probing superconductivity at nanoscale.