In this study we report on the light-emission characteristics of Si nanocrystals formed at the initial stages of anodization of bulk crystalline Si in the transition regime using extremely short pulses of anodic current. A considerable enhancement and a red-shift of the photoluminescence (PL) peak of the as-grown films under prolonged laser illumination in atmosphere was observed. Ageing or thermal oxidation in atmosphere at 300 °C caused similar red-shift and significant enhancement of PL relative to the as-grown films. In all cases the enhancement and the red-shift of the PL coincided with the appearance of O2-Si-H2 and O2-Si-H(OH) stretching modes in the Fourier-Transform-Infra-Red (FTIR) absorption spectra. Oxidation in dry oxygen at 900 °C caused red-shift of PL without enhancement. Finally removal of the oxide caused blue shift of PL. All these observations are discussed in the context of the quantum confinement model. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

We review our results on the structural and light-emitting properties of ultra-thin anodic silicon films grown by the electrochemical dissolution of bulk monocrystalline silicon at early stages of anodization. The films were grown using monopulses of anodization current covering the range from the regime of porous silicon formation to electropolishing. The samples were characterized by high resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy and photoluminescence.

The optical properties of ultra thin anodic silicon layers containing silicon nanocrystals were investigated by photoluminescence spectroscopy and Fourier transform infrared absorption spectroscopy. The films were grown by electrochemical dissolution of bulk crystalline silicon at the early stages of anodization using short monopulses of anodic currents ranging from the regime of porous silicon formation to the transition regime between porosification and electropolishing. The conditions for obtaining light emitting films and the origin of light emission will be discussed. © 2007 American Institute of Physics.

We report on the infrared transmission and light emission of Si-rich nitride (SRN) films prepared by low pressure chemical vapor deposition (LPCVD) from dichlorosilane (SiH2Cl2, DCS) and ammonia (NH3) mixtures. The main absorption band at about 830 cm- 1, attributed to Si-N vibration mode and observed in stoichiometric silicon nitride, shifted to slightly higher wavenumbers with increasing Si content in the SRN films. Annealing at temperatures higher than the deposition temperature induced a further shift of the main band to higher wavenumbers. Additionally, a new band appeared as a "shoulder" at about 1080 cm- 1, attributed to partial oxidation of the silicon nanocrystals. Photoluminescence (PL) obtained from the SRN films increased considerably and shifted to shorter wavelengths as the Si content decreased whereas annealing caused further enhancement and a slight shift to shorter wavelengths in comparison with the as-grown films. © 2007 Elsevier B.V. All rights reserved.

For a better understanding of the physical properties of semiconductor quantum dot ensembles, we have followed the behaviors of the transport and photoluminescence above, at, and below the percolation threshold of ensembles of Si quantum dots that are embedded in a Si O2 matrix. Our study revealed the roles of the interdot conduction, the single dot charging, and the connectivity in such systems. We conclude that while the first two determine the global transport, a connectivity dependent migration determines the coupling between the electrical and optical properties. © 2007 The American Physical Society.

An investigation of the optical properties of Si-rich silicon nitride films prepared by low pressure chemical vapor deposition (LPCVD) from dichlorosilane (SiH2Cl2, DCS) and ammonia (NH3) mixtures has been performed. From TEM analysis, it was found that the excess Si forms nanocrystals the size of which depends on the temperature. The real and the imaginary part of the refractive index of the films were calculated using spectroscopic ellipsometry by fitting the ellipsometric data in the range 1000-250 nm using the Tauc-Lorentz model. It was found that the optical constants of the films mainly depend on their chemical composition which can be controlled by the DCS/NH3 flow ratio. Annealing at temperatures up to 1100 °C for 4 h does not considerably affect the refractive index of the films. Depending on their stoichiometry and the annealing conditions applied after growth, some of the films emitted light in the visible at room temperature. This was attributed to the quantum confinement of carriers in the Si nanocrystals contained in the films. © 2007 Elsevier Ltd. All rights reserved.

We developed a method for fabricating ultra-thin (18-80 nm) light emitting amorphous films with embedded silicon nanocrystals by anodization of bulk crystalline Si in the transition regime between porosification and electropolishing using short mono-pulses of anodization current. The size of the nanocrystals decreased with increasing current density and it was in the range of 3-7 nm with current densities in the range of 130-390 mA cm-2. At the highest current density used the film/substrate interface was very sharp, while at lower current densities the interface contained nanostructured silicon spikes protruding from the substrate into the amorphous film. The samples were characterized by high resolution transmission electron microscopy, Fourier transform infrared spectroscopy and photoluminescence. © IOP Publishing Ltd.

We review our results on the structural and light-emitting properties of ultra-thin anodic silicon films grown by the electrochemical dissolution of bulk monocrystalline silicon at early stages of anodization. The films were grown using monopulses of anodization current covering the range from the regime of porous silicon formation to electropolishing. The samples were characterized by high resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy and photoluminescence. © 2007 by World Scientific Publishing Co. Pte. Ltd. All rights reserved.

In this study we investigated the magneto-transport properties of the ohmic contact between polycrystal-line NiMnSb thin films grown by pulsed laser deposition and n-type degenerate InSb (100) substrates. An unusual negative giant magnetoresistance (n-GMR) effect is found when the external magnetic field is parallel to the in-plane current direction. A similar effect is also observed when Ni films are deposited on InSb substrates. On the other hand, no n-GMR effect is displayed when the deposited film is nonmagnetic. Grazing-incidence X-ray reflectometry shows the formation of a low-density NiMnSb layer at the interface. The presence of such a layer coincides with the appearance of the n-GMR. We argue that the n-GMR effect is due to magnetic precipitates formed at the interface during the growth of the magnetic films. We propose that these precipitates align their magnetic moments in the direction of the external magnetic field and thus, the spin dependent scattering of the electrons is reduced. The effect of these precipitates on the magnetoresistance depends on the thermal processing of the system. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.