Pulsed measurements on the solid-electrolyte system, which proved very useful in the study of crystalline semiconductors, have been found to be equally effective when applied to hydrogenated amorphous Si films. Here, as well, the aSi:H/electrolyte interface is essentially blocking to current flow and, as a result, surface space-charge layers, ranging from large depletion to very strong accumulation conditions, can be induced and studied. In particular, valuable information can be gained on the density of the localized bulk states. Measurements in the depletion range under illumination yield directly the total density of occupied states in the entire energy gap. This is very useful in obtaining a quick and reliable assessment of the quality of the amorphous films. In high-grade films we find that the total density of occupied states is around 1018 cm−3. The data in the accumulation range, on the other hand, provide useful information on unoccupied states near the conduction band edge. The blocking nature of the amorphous Si/electrolyte interface is utilized also to apply a sweep-out technique for an accurate determination of μτ the product of the electron mobility and lifetime, even when this value is very low. In a rather poor-quality film, for example, we find μτ to be 5 × 10−8 cm2/V.

Measurements of the delayed-fluorescence excitation spectrum in anthracene could so far yield only the relative variation of the singlet-triplet absorption coefficient α with wavelength. In the present work the absolute magnitude of α is derived from studies involving the interaction of photo-generated triplet excitons with trapped electrons introduced into the sample by contact injection. Such an interaction results in the liberation of trapped electrons on the one hand and in the quenching of the triplet-exciton lifetime on the other. The former process is studied by photocurrent measurements while the latter is monitored by triplet lifetime measurements. The value of α so determined is (1.2, ± 0.2) × 10−3 cm−1 at the first singlet-triplet absorption peak (6780 A).

Photoluminescence (PL) spectra and their temperature dependence, as well as PL excitation and Raman spectra of Si-SiOx systems prepared by RF magnetron sputtering were investigated as a function of Si content. It was shown that PL spectrum of such systems consists of several bands. The correlation of shift of peak position of the lower-energy band from 1.38 to 1.54 eV with the change of size of Si nanocrystallites from 5 to 2.7 nm was observed. It was assumed that this PL band is connected with carrier recombination inside Si nanoparticles or with radiative transitions between a Si band and an interface level. It was shown that peak positions of the other observed bands (at 1.7, 2.06 and 2.32 eV) do not depend on the sizes of Si nanocrystallites. It was suggested that they are connected with silicon oxide defects based on the increase of intensities of these bands with increasing silicon oxide content. It was also shown that the excitation of PL is mainly due to light absorption in silicon nanocrystallites. Participation of hot carriers in excitation of defect-related bands was assumed. (C) 2002 Elsevier Science B.V. All rights reserved.

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 degreesC. 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. (C) 2003 Elsevier Science B.V. All rights reserved.

Investigations of photoluminescence, its temperature dependence, Raman scattering and IR absorption spectra were done for the study of the photoluminescence mechanism in porous silicon and Si enriched silicon oxide films. "Red" (1.6-1.7 eV) and "orange" (1.9-2.2 eV) photoluminescence bands are observed in both objects. Comparative investigations indicate that an oxide defect related mechanism is involved in the emission of PL bands in Si wires and silicon oxide films. Photoluminescence excitation mechanisms are discussed as well.

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.

Photoluminescence (PL), photoluminescence excitation (PLE), and Raman spectra of Si–SiOx layers were measured as a function of Si content. Samples were prepared by co-sputtering of Si and SiO2 and post-annealing. The average size of Si nanoparticles was estimated from Raman measurements. It was shown that, in general, the PL spectra consist of two bands with maxima in the 'red' and 'green' spectral ranges. The 'red' PL band is complex and contains two (IR and red (R)) components. The shift of the peak position of the IR component from 1.38 to 1.54 eV correlates with the decrease of the Si nanoparticle size from 5 to 2.7 nm. It was shown that this PL component could be ascribed to carrier recombination in silicon nanoparticles. The R component of the 'red' band as well as the 'green' band have similar dependences of the peak positions and intensities on the Si content and can be ascribed to defect-related luminescence. It was concluded that the light absorption in silicon nanocrystallites plays the main role in PLE process. Hot-carrier participation in the excitation of defect-related bands was deduced.

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.

Raman scattering spectra, the photoluminescence spectra and their dependence from the temperature, as well as atomic force microscopy investigations used for the studies the peculiarities of the photoluminescence bands in porous silicon and silicon in silicon oxide. It has been shown that red photoluminescence band in porous silicon is the complex and can be decomposed into two elementary one, The elementary band intensities very much depend from the surface structure of top porous silicon layer, The mechanisms of the luminescence bands in porous silicon and silicon oxide with Si are discussed as well.

Photoluminescence spectra and their dependence on the temperature have been used to study the peculiarities of the red photoluminescence in low-dimensional Si structures, such as porous silicon and silicon oxide films with an admixture of silicon. It has been shown that red photoluminescence band of Si wires is complex and can be decomposed into two elementary bands. Practically the same positions of photoluminescence bands are observed in silicon oxide films. Comparative investigation of photoluminescence temperature dependence in Si wires and silicon oxide indicates that oxide defect related mechanisms for photoluminescence bands are involved. The photoluminescence excitation mechanisms in both objects are discussed as well.

The enhancement of the Raman intensity from a porous layer compared to the signal from the silicon substrate was observed. It is assumed that this phenomenon is due to the specific form of pores that leads to the optical effect of focusing of scattered light near the bottom of the macropores. It was shown that the peak position and shape of the Raman line depend on the nanostructure of the pore bottom.

Photoluminescence (PL), photoluminescence excitation (PLE) and FTIR methods were used to study the PL excitation mechanism in porous silicon (PS).Two types of PLE spectra were observed, consisting of two (visible and ultraviolet) and one (only ultraviolet) bands.The intensities of each PLE band depend differently on the anodization conditions during aging and thermal treatment.Two excitation channels were shown to exist in PS.The visible PLE band at 300 K was attributed to light absorption of some species on the surface of Si wires.

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.

Hall effect, magnetoresistance, and electrical conductivity measurements, carried out on ZnO surface wells created by a large variety of methods, are analyzed in the frame of the weak-localization theory. The ZnO surface wells have some unique features that allow the investigation of the weak-localization effects: ZnO has a single valley conduction band; the Thouless length is much larger than the elastic mean-free path even at room temperature; the well accumulates the largest surface electron concentration obtained up to now in a surface quantum well; there are a large variety of preparation methods, some of them making it possible to modify independently both the width and the depth of the surface wells. These features allowed us to investigate: the presence of the weak-localization effect in the largest range of temperatures(1.6-300 K) reported up to now for a quantum well; the influence on the transport properties of the increase in the number of subbands in the well; the effect of the presence of more inelastic scattering mechanisms and their weights in the entire scattering process; and the passage from a quasi-two-dimensional system to a three-dimensional one. [S0163-1829(99)01932-3].

Photoluminescence (PL) and photoluminescence excitation (PLE) spectra studies as well as SIMS and FTIR methods were used for investigation of PL excitation mechanism of porous silicon (PS). It is shown that there are two types of PS PLE spectra, which consist of either two bands (visible and ultraviolet) or only ultraviolet one. The different dependencies of intensity of each PLE band upon anodization regimes as well as during aging and thermal treatment were observed Two excitation channels have been shown to be present in PS. The visible PLE band at 300 K has been attributed to light absorption of some species on Si wire surface.

Photoluminescence and excitation spectra measurements as well as SIMS and FTIR techniques were used to investigate the photoluminescence excitation mechanism of porous silicon. It is shown that there are two types of photoluminescence excitation spectra which consist either of two, visible and ultraviolet, or one, only ultraviolet, bands. The dependence of photoluminescence excitation spectra upon the various treatment (aging in vacuum, in air and in liquids) indicates that the excitation in the visible range occurs via light absorption of some species on the porous Si surface.

Low energy hydrogen ion implantation in ZnO creates an accumulation layer near the surface, giving rise to a quantum well. The corresponding self-consistent Hartree problem is solved by taking into account the donor distribution resulting from the implantation process. The values of the surface potential as a function of repelled away electron concentration are derived. The resulting data are compared with experimental values obtained from space-charge capacitance measurements. A comparative study between the semi-classical and self-consistent quantum treatments is presented.

We investigated the plasmon characteristics on luminescent porous silicon using electron energy loss spectroscopy. The samples were prepared from p-type crystalline silicon, (100) face, using the conventional electrochemical etching technique with the usual solution of HF, ethanol and water, followed by a critical point drying process. The energy of the bulk plasmon was measured both before and after sputter cleaning the sample with argon-ion bombardment. We found that initially the plasmon energy was slightly higher, ≈18 eV, than the plasmon energy of crystalline silicon. After sputter cleaning the sample with 5 keV Ar + ions, the plasmon energy increased to ≈20 eV. Exposure to the electron beam used for the measurements caused a slow upward shift of the plasmon energy as a function of time, toward a saturation energy of 22-23 eV, an energy close to the plasmon energy of SiC. Auger spectroscopy performed in parallel showed an increasing carbon coverage. We prepared also samples without ethanol in the etching solution and/or with no critical point drying. Samples that did not undergo the critical point drying process showed consistently a practically constant plasmon energy, with almost no change upon sputtering and/or exposure to the electron beam. On the other hand, samples that were prepared with or without ethanol but using the critical point drying process, showed an appreciable increase in the plasmon energy upon exposure to the electron beam. We conclude that traces of CO 2 , used in the critical point drying process, are stored in the pores of the porous silicon surface and serve as a source of carbon. Apparently, upon activation by argon bombardment or by the electron beam, the carbon interacts with the porous Si surface forming a carbon-silicon compound, most probably SiC.

The effect of preparation regimes on the oxide composition, the number of dangling bonds and photoluminescence spectra have been investigated. The influence of the oxidation process during additional anodization of porous silicon in NaCl electrolyte on photo- and electroluminescence spectra have been studied also.