J. Palacios Gómez

Complex nature of the red photoluminescence band and peculiarities of its excitation in porous silicon

Abstract Photoluminescence and photoluminescence excitation spectroscopies, scanning electron microscopy, and atomic force microscopy were used to study the photoluminescence mechanism in porous silicon. The dependences of photoluminescence parameters on electrochemical etching regimes, excitation light wavelength, and vacuum ageing have been investigated. We show that intensive and broad “red” luminescence band (∼600–800 nm) is non-elementary, and can be decomposed into three elementary bands. The mechanisms of the elementary bands are discussed.

Photoluminescence of Ge nano-crystallites embedded in silicon oxide

Photoluminescence (PL), transmission electron microscopy, Raman scattering spectra and extended X-ray absorption fine structure have been investigated in silicon oxide films enriched by Ge in as-grown state and after their thermal annealing at 800 °C. The dependences of PL peculiarities on the concentration of Ge, as well as on the existence (or absence) of Ge nano-crystallites in silicon oxide films are analyzed.

Evidence of extinction in strongly textured high-purity copper

In order to test the influence of extinction on texture measurements, pole figures of four copper samples were measured using neutron diffraction with three different wavelengths. The copper samples had previously been cold rolled to different extents and partially annealed. Therefore, three of the samples presented a relatively strong texture and the fourth sample a relatively weak texture. In this study, the results from equivalent pole figures were compared between the different samples. These investigations showed that, in general, except for the sample with weak texture, the 222 reflection showed higher pole density maxima than the 111 reflection. Since all measuring conditions were the same for both reflections, this difference was attributed to extinction. The pole density maxima of strong reflections also revealed a slight tendency to lower values with decreasing wavelengths. This phenomenon is attributed to the fact that more reflections exist at shorter wavelengths and therefore an increase in secondary extinction is measurable at these wavelengths.

Comparative investigations of surface structure, photoluminescence and its excitation in silicon wires

Abstract The dependence of the photoluminescence (PL) and PL excitation spectra on the porous silicon top surface structure and the oxide composition on it has been investigated. Researches were carried out using the following methods: PL, PL excitation, electron paramagnetic resonance, atomic force microscope and X-ray photoelectron emission spectroscopy. Results indicate a direct correlation between the suboxide content and roughness structure on the surface with PL intensity. No correlation was noted between the PL intensity and the concentration of Si dangling bonds (non-radiative recombination centers). These results have given further support to a suboxide-related color center on the Si/SiO x interface as the source of the intense red luminescence of silicon wires.

Some reasons of emission variation in InAs quantum dot-in-a-well structures

Photoluminescence (PL) and X ray diffraction have been studied in InAs quantum dots (QDs) embedded in symmetric In0.15Ga1-0.15As/GaAs quantum wells (dot-in-a-well, DWELL) with QDs grown at different temperatures. The density of QDs decreases from 1.1×1011 down to 1.3×1010 cm-2 with increasing the QD growth temperatures from 470 to 535°C. The QD density decreasing in DWELLs is accompanied by the non monotonous variation of QD parameters. The PL intensity increases and the PL peak shifts to low energy in structures with QDs grown at 490 and 510°C. On the contrary the structures with QDs grown at 525 and 535°C are characterized by lower PL intensities and PL peak positions shifted to higher energy. The method of X-ray diffraction has been applied with the aim to study the variation of elastic strain in DWELL structures with QDs grown at different temperatures. It was shown that the minimum of elastic strain corresponds to DWELL with QDs grown at 490-525 °C. For lower (470 °C) and higher (535 °C) QD growth temperatures the level of compressive strain increased in DWELLs. The reasons of strain variation are discussed as well.

Nature of the red photoluminescence in porous silicon

Photoluminescence and its excitation, Raman scattering, as well as Atomic Force Microscopy investigations were used to study the photoluminescence mechanism in P-Si. The dependencies of all characteristics on P-Si preparation regimes, the duration of the electrochemical etching process, have been investigated. The influence on the PL spectra of the variation of the excitation light wavelength and storage in vacuum were studied as well. We have shown that the red luminescence band can be decomposed into three elementary bands.