Y. Goldstein

Mechanism of photoluminescence of silicon oxide films enriched by Si or Ge

Photoluminescence peculiarities of silicon oxide films enriched by Si or Ge have been investigated. Photoluminescence (PL) and Raman spectra were measured before and after thermal annealing at 800 °C. The dependences of PL peculiarities on the concentration of Si and Ge, as well as on the existence (or absence) of Si (Ge) quantum dots (QDs) in silicon oxide films are analyzed for the photoluminescence mechanism study in the above-mentioned systems.

Auger electron spectroscopy for quantitative analysis

A simple mathematical analysis shows that unless the ratio of the instrumental resolution width to the natural Auger linewidth is less than about 0.3, the measured line intensities do not represent accurately the atomic concentrations. To overcome this difficulty, a universal curve is presented whereby the experimentally measured line intensities can be corrected so as to represent quite accurately the relative atomic concentrations in one’s sample. Unfortunately, however, the available sensitivity data required for quantification were not always measured with sufficient instrumental resolution. It is our contention that there is a need for new sensitivity measurements in which the required resolution is ensured.

Two-dimensional plasma oscillation on ZnO surfaces

Abstract Angle resolved, low energy electron spectroscopy is used to study collective excitations on accumulaton layers on ZnO. As the electron density in the accumulation layer is increased a prominent loss peak is observed which, at specular reflection angles, shifts from ~ 67 meV in the absence of surface electrons to ~320 meV in strong accumulation layers. This behavior is well accounted for theoretically in terms of scattering by two-dimensional plasmon-like collective surface excitations. A shift in energy of the loss peak position as a function of δθ, the deviation angle from specular reflection, was also measured.

Investigation of aging process of Si–SiOx structures with silicon quantum dots

In this work the aging processes of magnetron-sputtered Si–SiOx structures with silicon quantum dots are investigated by photoluminescence, electronic paramagnetic resonance, infrared absorption, and Raman-scattering methods. It is observed that oxidation of the silicon dots, change in the defect concentration in the oxide matrix, and oxidation of the silicon amorphous phase occur during storage in air at room temperature. A comparison of the variation of parameters of sputtered structures and porous silicon layers caused by the aging process is made. It is shown that the rate of oxidation of silicon dots and the decrease of their sizes in sputtered structures are essentially less than that in porous silicon. It is also shown that in Si–SiOx, layers in contrast to porous silicon, the intensity and spectral position of the emission band caused by exciton recombination in Si crystallites do not change practically during aging.

Relation between electroluminescence and photoluminescence in porous silicon

Abstract We present combined measurements of electroluminescence (EL) and photoluminescence (PL) in p-type porous silicon. The EL spectra were measured using an electrolyte contact for electron injection into the porous face of the sample. Upon applying the current, the EL intensity first rises with time, reaches a maximum, and then decays to zero. (The whole process takes about half an hour.) At the same time, the peak of the EL spectrum shifts from ≈850 nm in the beginning to ≈600 nm at the end of the process. The PL, which was measured simultaneously, peaked at ≈750 nm in the beginning and was much wider than all of the EL spectra. Towards the end of the EL process, the red part of the PL spectrum practically disappears. This shifts the PL peak towards the blue, to about the same wavelength as the EL peak (≈600 nm) and the spectrum becomes much narrower, comparable to the EL spectrum. The voltage across the sample during the EL process shows a moderate increase up to the point where the EL disappears, and then the voltage rises steeply. This behavior is associated with the build-up of a thin oxide layer on the porous surface. The combined results of EL and PL, and especially the disappearance of the red part in the photoluminescence spectrum at the end of the EL process, suggest that in addition to quantum confinement, localized surface states play an important role in the luminescence process, at least in the red part of the spectrum. Such states may be associated with adsorbed species and disappear upon oxidation.

Non-parabolicity in the lowest conduction band of CdS

Abstract Pulse measurements on the CdS/electrolyte system are used to induce and study space-charge layers at the CdS surface. Such measurements show that the free-electron-like lowest conduction band in hexagonal CdS is highly non-parabolic. A simple model for the structure of this band, which assumes parabolicity up to 0.125 eV above the band edge and a linear dependence of the energy on the wavevector at higher energies, accounts well for the experimental results. The density of states function that emerges from these results is compatible with reported theoretical calculations. In addition, the measurements indicate that surface states are practically absent at the CdS surface in contact with the electrolyte. They also shed light on the process of charge leakage across the CdS/electrolyte interface, leakage that occurs mostly when strong accumulation layers are induced.

Photoluminescence of silicon oxide films enriched by Si or Ge

Photoluminescence (PL) and Raman spectra of silicon oxide films enriched by Si or Ge have been investigated before and after thermal annealing at 1150°C and 800°C, respectively. The dependences of PL peculiarities on the concentration of Si and Ge, as well as on the existence (or absence) of Si (Ge) quantum dots in silicon oxide films are analyzed. It is concluded that the PL spectrum of the oxide films enriched with Ge and at least the high-energy part of the spectrum of the films enriched with Si are due to defects in the silicon oxide films.

Comparative investigation of photoluminescence of silicon wire structures and silicon oxide films

Photoluminescence spectra and their dependence on temperature as well as Raman scattering spectra and Atomic Force Microscopy investigations have been used to study the peculiarities of the red photoluminescence band in low-dimensional Si structures, such as porous silicon and silicon oxide films. It has been shown that the red photoluminescence band of porous silicon is complex and can be decomposed into two elementary bands. It was discovered that elementary band intensities depend very much on surface morphology of porous silicon. The same positions of the photoluminescence bands are also observed in silicon oxide films for different oxide composition. Comparative investigation of the PL temperature dependences in porous silicon and silicon oxide films indicates that silicon-oxide defect related mechanisms of some elementary photoluminescence bands are involved.

Photoelectromagnetic effect in p‐type HgCdTe layers grown by liquid phase epitaxy

Photo‐electro‐magnetic effect measurements of p‐type Hg1−xCdxTe layers are made at 80 K as a function of the magnetic field. A negative (anomalous) effect is observed. The basic properties of the minority carriers, mobility, lifetime, surface and interface recombination rates, are determined from best fitting of the experimental data to the theory.

Yields, sensitivities and natural line shapes of high-energy Auger lines: Ta, W, Pt, Au, Pb and Bi

Abstract We present high-resolution measurements of the natural Auger line shapes of the two highest-energy MNN lines of Ta, W, Pt, Au, Pb and Bi. It was found that all the lines studied are quite narrow, having a width of about 2 eV. The main lines are accompanied by smaller satellite peaks. While these measurements are very suitable for determining the natural line shapes, they are inadequate for obtaining the line intensities. The atomic sensitivities were therefore measured with a resolution of 0.4% of the Auger energy (somewhat better than the commonly available resolution). With this resolution it is impossible to resolve the fine structure of the lines and also gross errors are incurred in the measurements of the atomic sensitivities. We corrected these measured sensitivities by applying our theoretical analysis developed previously. The correction factors for the sensitivities are around 10. These large factors represent also the errors incurred in the as-measured sensitivities if no correction is applied. The detailed line shapes, as derived from the high-resolution measurements, and the corrected sensitivities, as obtained from our analysis, are the true characteristics with which any theoretical calculations of Auger transitions should be compared.