Oxygen Absorption in Free-Standing Porous Silicon: A Structural, Optical and Kinetic Analysis (original) (raw)
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Study of anodic oxidation of porous silicon: relation between growth and physical properties
Journal of Luminescence, 1993
In this work, we report a preliminary study of anodic oxidation of p + porous silicon in order to obtain Si wires of lateral controlled size. RBS and SIMS spectra show that the whole porous layer is uniformly oxidized independently of the anodic current. The lateral size of Si wires can be controlled by varying the potential difference between the silicon electrode and a platinum cathode from 0 to 10 V. At 10 V, the electrical contact between the substrate and the porous layer is broken. Then the porous layer is practically no more oxidized. At this stage, the lateral size ofthe Si wire has been estimated to 4 nm. Electron Paramagnetic Resonance (EPR) measurements were performed which indicate that there are oxygen vacancies in Si0 2 and that the trigonal (Ill) Pb center is not the dominating paramagnetic defect as in as-prepared porous layer or in porous layer thermally oxidized. The photoluminescence intensity increases with the potential difference but it is much lower than that obtained in p~porous layer of 80% porosity. This weak photoluminescence intensity may be explained by a bad passivation of Si surface or/and to the fact that the major part of the Si wires have lateral size too high to lead to visible luminescence. = 0.35 x (1 y/2).
20. The Role of Oxygen in the Photoluminescence of Porous Silicon: Some Recent Observations
Physica Status Solidi A, 2000
The role of oxygen in the luminescence from porous silicon is examined using a synchrotron spec-troscopic technique often known as XEOL (X-ray Excited Optical Luminescence) and associated optical XAFS (X-ray Absorption Fine Structures using photoluminescence yield). The tunability of synchrotron light permits the probing of the inner valence and the core levels of silicon and oxygen in porous silicon. These processes are associated with site specificity and probing depth variations depending on the absorption coefficient. Luminescence excited with photons in the inner valence region (15±40 eV) and at the oxygen K-edge are reported. From these results together with previous and new Si K-edge and L 3,2-edge studies, a picture of the role of oxygen emerges. Introduction Although there has been considerable work on the role of oxygen in the luminescence from porous silicon [PS], the debate continues [1±9]. It is now generally accepted that oxygen does play some role: chemical capping of the nanocrystallite (stabilizing nanocrystallites and introducing interfacial states tailing into the band gap) [1, 2] and forming SiO 2 encapsulating layers in which defects produce luminescence [6±9]. However, the details of these roles are still not fully understood. In this paper, we present new results from a synchrotron radiation (SR) induced photoluminescence study. The tunability of the SR light permits the study of site-specific photolumines-cence under favorable experimental conditions as well as variation in probing depth. This technique is often referred to as XEOL (X-ray excited optical luminescence) [10]. Using the high energy resolution of absorption spectroscopy and the significantly different spectral behavior between silicon and silicon oxide (large chemical shift), one can preferentially excite atomic Si and O sites, and one can further select chemically different sites: Si atoms bonded to oxygen and those that do not. It is also important to note that in the photon energy region of interest to porous silicon, the soft X-ray is totally absorbed by the PS specimen. This property has some ramifications. Thus it is useful to examine how the incident photon is attenuated in porous silicon in terms of the one-absorption length (1/e transmission of incident photon, 63% absorption) of Si and SiO 2 , components of porous silicon. Table 1 lists the attenuation length of the inci
Excitation spectroscopy of anodically oxidized porous silicon
Journal of Luminescence, 1996
Photoluminescence (PL) and photoluminescence excitation (PLE) studies are carried out on porous silicon (PS) layers anodically oxidized in NH4N03-ethylenglycol electrolyte. PLE spectra reveal monocrystalline silicon like features after removing the oxide shell of crystallites by chemical etching. Its reconstruction during oxidation in air atmosphere seems to increase mechanical stresses in silicon nanocrystallites. As a result, the PLE spectra, absorption and emission properties of PS are changed considerably.
Natural Oxidation of Porous Silicon
This work reports the evolution of the chemical species at the porous silicon (PS) surface and the room temperature visible photoluminescence (PL) from PS naturally oxidized for one year. The Si-O and Si-Hx-O bonds increase due to the aging process, but the hydrogen surface coverage is preserved. The PL spectra are blue shifted as the samples are naturally oxidized.
The role of oxidation on porous silicon photoluminescence and its excitation
Thin Solid Films, 2001
The effect of preparation regimes on the oxide composition, the number of dangling bonds, the photoluminescence and its excitation spectra have been investigated. The influence of the oxidation process during aging of porous silicon at ambient Ž. Ž. atmosphere and annealing in dry oxygen has been investigated via photoluminescence PL , PL excitation PLE , electron Ž. Ž. paramagnetic resonance EPR and X-ray photoelectron emission spectroscopy XPS. Results indicate a direct correlation between the suboxide content and the PL intensity, while no correlation was noted between the PL intensity and the Ž. concentration of Si dangling bonds non-radiative recombination centers. These results given further support to a suboxiderelated color center as the source of the intense red luminescence.
18. Influence of sample oxidation on the nature of optical luminescence from porous silicon
Applied Physics Letters, 2000
Site-selective luminescence experiments were performed upon porous-silicon samples exposed to varying degrees of oxidation. The source of different luminescence bands was determined to be due to either quantum confinement in nanocrystalline silicon or defective silicon oxide. Of particular interest is the defective silicon-oxide luminescence band found at 2.1 eV, which was found to frequently overlap with a luminescence band from nanocrystalline silicon. Some of the historical confusion and debate with regards to the source of luminescence from porous silicon can be attributed to this overlap.
Photo-oxidation effects in porous silicon luminescence
Physical Review B, 2004
We investigate the photoluminescence ͑PL͒ evolution of porous silicon samples when exposed to air in darkness and under illumination. Oxygen incorporation is monitored through ir spectroscopy. Fourier transform infrared measurements show that samples exposed to air in darkness exhibit low oxidation rates whereas its PL spectra remain unchanged. On the other hand, samples exposed to air under illumination show a remarkable change in its PL together with a drastic increase in the oxidation rate. A well defined PL peak starts to grow at the expense of a peak located at lower energies, which is present in the PL spectra of the as-prepared samples. The set of PL spectra obtained during the evolution shows an isostilbic point that suggests the existence of two emitting components kinetically correlated. The application of the factor analysis technique confirms this asseveration and enables us to obtain the spectrum of each single emitting component. The oxidation behavior, together with the shape and evolution of the PL spectra, are explained in terms of the quantum wires hypothesis combined with an oxidation mechanism with significant nucleation. The whole set of results demonstrates that quantum size effects may rule the photo-oxidation of the porous silicon structure, and gives strong support to a quantum confinement model for porous silicon PL.
Advances in Optical Technologies, 2012
The porous silicon (PSi) layers were formed on p-type silicon (Si) wafer. The six samples were anodised electrically with 30 mA/cm 2 fixed current density for different etching times. The structural, optical, and thermal properties of porous silicon on silicon substrates were investigated by photoluminescence (PL), photoacoustic spectroscopy (PAS), and UV-Vis-NIR spectrophotometer. The thickness and porosity of the layers were measured using the gravimetric method. The band gap of the samples was measured through the photoluminescence (PL) peak and absorption spectra, then they were compared. It shows that band gap value increases by raising the porosity. Photoacoustic spectroscopy (PAS) was carried out for measuring the thermal diffusivity (TD) of the samples.
Materials Science and Engineering B, 2003
In this work, we study optical and compositional properties of stain-etched porous silicon (PS) passivated by means of anodic oxidation or thermal treatments in a N 2 atmosphere. We search a passivation method that allows us to stabilise the surface properties of this material and to make it attractive to its implementation in a low-cost silicon-based solar cell fabrication process. We observe that the thermal treatment maintains the reflectance coefficient at very low values, and the anodic oxidation generates surfaces with a more homogeneous oxide composition than the thermal treatment. These results are appropriate with the requirements for future solar cells that can use these passivated porous layers as antireflection coatings.
Morphological Aspects of Oxidized Porous Silicon Prepared by Photo Electrochemical Etching
2010
This paper reports morphological properties of porous silicon and oxidized porous silicon, prepared by photo electrochemical etching from n-type silicon wafers as a function of experimental parameters. Scanning electron microscopic (SEM) Observations of porous silicon layers were obtained before and after rapid thermal oxidation process under different preparation and oxidation conditions .The surface morphology, Pore diameter, wall thickness, pore shape and porosity values were, studied based on microstructure analyses of (SEM) images.