Photoluminescence Spectra Of Porous Silicon Research Articles

The Influence of the Energy of Ar$${}^{\mathbf{+}}$$ Ion Implantation on the Photoluminescence of Porous Silicon

Irradiation of porous silicon with Ar $${}^{+}$$ ions at energies from 100 to 400 keV and fluence of $$10^{12}$$ cm $${}^{-2}$$ was carried out. The effect of ion irradiation at different energies of incident particles on the photoluminescence spectrum of porous silicon has been studied. it has been shown that the photoluminescence spectrum consists of two components. One of then is associated with the presence of structural defects; another, with the surface states on the complex surface of porous silicon. A method for estimating the thickness of the luminescent layer based on the analysis of the photoluminescence peak associated with defects is proposed.

The Effect of Argon Ion Irradiation Parameters on the Photoluminescence Spectrum of Porous Silicon

In this paper, the irradiation of porous silicon with Ar $${}^{+}$$ ions with the energies of 100 and 200 keV and fluences from $$10^{12}$$ cm $${}^{-2}$$ up to $$3\times 10^{13}$$ cm $${}^{-2}$$ has been performed and studied. The effect of ion irradiation at different fluences and energies of incident particles on the photoluminescence spectrum of porous silicon has been analyzed. It has been shown that ion irradiation leads to a shift of the photoluminescence maximum, which grows with increasing energy. An increase in the fluence reduces the photoluminescence intensity, but, at the same time, has no effect on the magnitude of the maximum shift. The main mechanisms of the photoluminescence in porous silicon are also discussed.

Photoluminescence study of porous p-type silicon: Identification of radiative transitions

The research discussed in this paper focused on a systematic methodology to elucidate the controversy about transitions responsible for the photoluminescence (PL) spectrum from porous silicon (PSi) layers etched on a p-type Si wafer, to understand the nature of light emitting mechanisms from PSi. The PL spectrum of PSi, as a function of temperature, shows the existence of broad peaks, initially associated with stable surface states. However, the PL studies as a function of time, under continuous laser fluency, shows the presence of electronic states due to silicon columns (quantum confinement) and the metastable surface states. Finally, the PL studies, during which the laser was cut off for several hours, confirm that the surface states are metastable. Based on the information provided by these studies, the interpretation of the results indicates that the PL spectrum of PSi is a superposition of porous surface states and states originated in the porous layer considered as a pseudo lattice of the Si bulk.

Influence on the Porous Silicon Photoluminescence By Magnetic Nanostructures

In this framework luminescent porous silicon (PSi) is filled with a magnetic metal (e.g. Ni) to influence the photoluminescence due to the presence of metal deposits. This happens in two ways. On the one hand the surface plasmon of the metal deposits is exploited to modify the luminescence and on the other hand it is influenced by an external magnetic field. Due to the metal filling of the porous silicon the photoluminescence is blue-shifted and furthermore an increase of the intensity is observed. The influence of the magnetic metal filling on the optical properties is discussed and the magnetic characterization of the nanocomposits is presented. The porous silicon is fabricated by anodization of a moderately doped p-silicon wafer. The electrolyte consists of hydrofluoric acid, Ethanol and distilled water (1:2:1). The metal deposition has been performed by pulsed electrodeposition in using a NiCl2 and NiSO4 solution. First the optical properties of the luminescent PSi are investigated, second Ni is deposited within the porous silicon samples and subsequently the nanocomposite specimens are characterized optically again and also magnetically. The samples are structurally characterized by SEM, EDX and TEM. The optical properties are investigated with respect to the shift of the photoluminescence due to the metal filling. Photoluminescence spectra of bare PSi show a maximum around 620 nm whereas in the case of Ni filled samples the peak is blue-shifted to around 580 nm and the luminescence intensity is increased. Figure 1 shows the comparison of the photoluminescence of two Ni-filled samples with different metal deposition time. Concerning the magnetic properties of the nanocomposite the embedded Ni structures can be superparamagnetic from the size of the pore diameters but due to the branched morphology the achieved deposits tend to be interconnected and thus do not offer necessarily a superparamagnetic behavior. Also temperature dependent magnetization measurements give no hint for a superparamagnetic behavior. Field dependent magnetization measurements performed with the magnetic field applied perpendicular and parallel to the sample surface show a high magnetic anisotropy. It can be clearly seen that the samples offer a film-like behavior due to the interconnected Ni structures which is represented by the easy axis parallel to the surface. In the frame of this work the optical characterization of luminescent PSi with respect to its photoluminescence compared with Ni filled samples is discussed in detail as well as the corresponding magnetic properties of the nanocomposites. Furthermore the influence of an external magnetic field on the optical properties is elucidated. The presented systems are promising candidates for applications in optoelectronics and also for magneto optical integrated devices. Figure 1. Photoluminescence spectra of porous silicon with incorporated Ni for two different deposition times. Figure 1

Temperature dependence of photoluminescence peaks of porous silicon structures

Abstract Evaluation of photoluminescence spectra of porous silicon (PS) samples prepared by electrochemical etching is presented. The samples were measured at temperatures 30, 70 and 150 K. Peak parameters (energy, intensity and width) were calculated. The PL spectrum was approximated by a set of Gaussian peaks. Their parameters were fixed using fitting a procedure in which the optimal number of peeks included into the model was estimated using the residuum of the approximation. The weak thermal dependence of the spectra indicates the strong influence of active defects.

Effect of gamma irradiation on the photoluminescence of porous silicon

The effect of gamma irradiation on the luminescence properties of porous silicon produced by the electrochemical technique is studied. Changes in the photoluminescence intensity between irradiation doses and over a period of several days after the last irradiation are recorded. The quenching of photoluminescence at low irradiation doses and recovery after further irradiation are registered. It is found that porous silicon is strongly oxidized after gamma irradiation and the oxidation process continues for several days after irradiation. It is conceived that the change in the photoluminescence spectra and intensity of porous silicon after gamma irradiation is caused by a change in the passivation type of the porous surface: instead of hydrogen passivation, more stable oxygen passivation is observed. To stabilize the photoluminescence spectra of porous silicon, the use of fullerenes is proposed. No considerable changes in the photoluminescence spectra during irradiation and up to 18 days after irradiation are detected in a porous silicon sample with a thermally deposited fullerene layer. It is shown that porous silicon samples with a deposited C60 layer are stable to gamma irradiation and oxidation.

Characterization of surface changes on silicon and porous silicon after interaction with hydroxyl radicals

The objective of this study was to investigate the changes in the optical and surface properties of crystalline silicon and porous silicon as a result of their interaction with hydroxyl radicals. In the initial stage, the change in the interfacial free energy of crystalline silicon and porous silicon was analyzed through contact angle measurements. These measurements indicated that, for these substrates, an increase in the degree of hydrophilicity of the surface occurs in every instance. However, when the substrates were immersed in Fenton solution and hydrogen peroxide electrochemically generated (electro-Fenton process), there was a more significant variation in the hydrophilic property within a short period of time. The changes in the photoluminescence spectra of porous silicon were also analyzed with various media. For the porous silicon/Fenton system, a decrease in intensity and a shift of the PL to longer wavelengths was observed. These changes were attributed to a change in the nature of the surface functional groups on the substrate from porous silicon hydrogen-terminated to hydroxyl-terminated when the surfaces were exposed to Fenton solution. Finally, the charge collection efficiency was studied via intensity-modulated photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy. These experiments provided information about the fraction of the substrate charge carriers that do not participate in the recombination process.

THE EFFECT OF THICKNESS OF SILVER THIN FILM ON STRUCTURAL AND OPTICAL PROPERTIES OF POROUS SILICON

In this study, porous silicon (PS) samples were prepared on [Formula: see text]-type silicon (100) wafers by electrochemical etching method, varying the current density from 20 to 100[Formula: see text]mA/cm2and keeping constant HF concentration (10%) and etching time of 15[Formula: see text]min. Then, Ag thin films, which have 10, 50 and 100[Formula: see text]nm film thicknesses, were deposited on PS layers by using thermal evaporation to investigate the influence of Ag film thickness on structural and optical properties of PS. The structural and optical properties of PS and Ag deposited PS layers have been investigated by XRD, FE-SEM, Raman and photoluminescence (PL) spectroscopy. FE-SEM XRD and Raman analyzes indicate that average pore size and porosity of PS layers increase with the increasing current density. Further, Ag nanoparticles have embedded in pore channel. PL measurement reveals that higher porosity of PS would be better to form the Ag–PS nano-composite material leading to stronger PL band. The PL spectra of PS and Ag–PS samples indicate that PL bands show blue shift with increasing current density and film thickness. Consequently, it has been found that the structural and optical properties of PS depend on current density and Ag film thickness individually.

Peculiarities of photoluminescence of porous silicon with luminescent liquid crystal fillers

Photoluminescence spectra of porous silicon filled by luminescent liquid crystals 5CB and H109 were investigated. It was observed that there were photoluminescence bands corresponding to both porous silicon and liquid crystal in experimental spectra. In addition, the band corresponding to porous silicon increases in comparison with photoluminescence of porous silicon without the filler. Experimental results are explained by the radiating and nonradiating energy transfer from liquid crystal to porous silicon.

Effect of Metallic Ions on Photoluminescence of Porous Silicon

In the present paper, we have not only investigated the top surface and cross-section morphology, but also measured photoluminescence spectra characteristic of porous silicon after deposition of metallic ions by electrochemical deposition employing scanning electron microscopy (SEM) and spectrometer, respectively. It is apparent from the SEM images that the microstructure of porous silicon is seriously ruined by the metallic ions deposited by electrochemical deposition. Most interesting is the finding that in the photoluminescence spectrum of porous silicon after the deposition of metallic ions such as AL3+ and Cu2+, the luminescence band gradually is quenched as the electrochemical deposition progressed. A careful consideration of the results obtained show that according to the basic theory of well-established quantum confinement model, the quenching of photoluminescence spectra of porous silicon may well be attributed to the microstructure fell into ruin. On the other side of the fence, we can interpret the physical origin of the phenomenon in view of the presence of metallic ions which give rise a series of energy level deep in the band gap of porous silicon.

The effect of silicon crystallographic orientation on the formation of silicon nanoclusters during anodic electrochemical etching

Possible ways for increasing the photoluminescence quantum yield of porous silicon layers have been investigated. The effect of the anodization parameters on the photoluminescence properties for porous silicon layers formed on silicon substrates with different crystallographic orientations was studied. The average diameters for silicon nanoclusters are calculated from the photoluminescence spectra of porous silicon. The influence of the substrate crystallographic orientation on the photoluminescence quantum yield of porous silicon is revealed. A model explaining the effect of the substrate orientation on the photoluminescence properties for the proous silicon layers formed by anode electrochemical etching is proposed.

Resonant Energy Transfer from Porous Silicon to Iodine Molecules

The electronic excitation energy transfer between excitons in porous silicon and iodine molecules in an organic solution is studied. From the time-resolved photoluminescence the rate of the energy transfer is increased with approaching a wavelength region where the photoluminescence spectrum of porous silicon overlaps the absorption spectrum of iodine molecules, and with increasing the radiative recombination rate of porous silicon. We show that the dependence of the rate is well explained by Förster type dipole-dipole interaction mechanism in which the diffusion of the assemblies and molecules is taken into consideration. Furthermore, it is found that the efficiency of the energy transfer strongly depends on the emission wavelength at low iodine concentration.

The effect of oxidation on the efficiency and spectrum of photoluminescence of porous silicon

The photoluminescence spectra of porous silicon and their temperature dependences and transformations on aging are studied. It is shown that the infrared band prevailing in the spectra of as-prepared samples is due to exciton recombination in silicon crystallites. On aging, a well-pronounced additional band is observed at shorter wavelengths of the spectra. It is assumed that this band is due to the recombination of carriers that are excited in silicon crystallites and recombine via some centers located in oxide. It is shown that the broad band commonly observable in oxidized porous silicon is a superposition of the above two bands. The dependences of the peak positions and integrated intensities of the bands on time and temperature are studied. The data on the distribution of oxide centers with depth in the porous layer are obtained.

Effect of ageing on the statical and time-resolved photoluminescence spectra of porous silicon

This paper reports on the ageing effect of porous silicon studied by statical and time-resolved photoluminescence spectroscopy. An increase in the full-width at half-maximum of the statical photoluminescence spectra of porous silicon from 200meV to 500meV after ageing of 24 hours in the air is observed and can be attributed to added emission mechanism via self-trapped electrons. The blue zone in the time-resolved photoluminescence spectra is found only after ageing of 72 hours in the air and the luminescence intensity of this zone increases by increasing the duration of the ageing. These results suggest that the intense and stable blue-light emission of porous silicon in the air may arise from defects in silicon oxide.

The nature of red emission in porous silicon

The photoluminescence spectra of porous silicon at 77 and 300 K and their transformation during aging were investigated. The competition of two radiative recombination channels that have a common excitation mechanism was observed. It is shown that only one of them, which causes infrared emission band and is present in as- prepared samples, is connected with excitonic recombination in Si nanocrystals. The second one that causes red emission band appears during aging is supposed to be connected with carrier recombination through oxide-related defects. It is shown that this channel dominates in aged samples.

Porous silicon upon multicrystalline silicon: Structure and photoluminiscence

Ultrathin porous silicon layers have been stain-etched upon multicrystalline silicon (multi-Si) substrates. We studied optical and structural properties of porous silicon by photoluminescence, photo-luminescence excitation, reflection, atomic force microscopy and scanning tunnel microscopy methods. It was observed that the thickness of porous silicon did not exceed 20 nm. The photoluminescence method has shown that photoluminescence spectra of porous silicon of different grains have shown that they differ insignificantly (∼10%) in intensity. It was found that por-Si layers with optimal antireflection characteristics was obtained during etching time 7 min. In the paper the comparison of the reflection characteristics of investigated samples por-Si with industrial antireflection coating is presented.

Fluctuation theory of photoluminescence of porous silicon

A theory of photoluminescence (PL) kinetics of porous silicon (PS) is developed. In this theory, the approach suggested by the authors earlier is extended to the case of finite temperatures. The theory is based on the concept of electron-hole recombination, which occurs in structural units of PS both through the tunneling mechanism (playing a role even for T=0 K) and through thermally activated diffusion of photoexcited carriers. The PL kinetics is analyzed in terms of two models considered in the literature, in which PS is treated as a random ensemble of spherical nanocrystallites or quantum wires. The results are applied to interpret experimental data on the kinetics and instantaneous PL spectra of PS. Although both models basically provide an adequate quantitative description of the experimental data at both low and room temperatures, the model of spherical nanocrystallites seems preferable.

Near-field spectroscopy of porous silicon microcavity samples

Near-field optical spectroscopy has been used to investigate photoluminescence features of porous silicon microcavity samples with a subwavelength space resolution. The emission is found to be markedly dependent on the lateral position, with the presence of relatively narrow spectral features peaked at different wavelengths in the range 610–690 nm. Furthermore, the spectrum obtained by summing up spectra taken at different sampling points (relative displacement ∼100 nm) recovers the standard (macroscopic) photoluminescence spectrum of porous silicon, except for the presence of a dip around the resonance wavelength of the microcavity resonator.

Blue shift of photoluminescence spectrum of porous silicon by helium ion irradiation

Effects of helium ion irradiation on photoluminescence spectrum of porous silicon were investigated. Photoluminescence spectra were measured for silicon prepared by only anodization (porous silicon), by only helium ion irradiation, and by helium ion irradiation before or after anodization. The porous silicon prepared only by anodization showed a photoluminescence spectrum with a peak intensity at 650 nm. The silicon prepared only by helium ion irradiation had no photoluminescence. Silicon prepared by helium ion irradiation followed by anodization showed a blue shift in the photoluminescence spectrum. The blue shift increased as a fluence of helium ion although the intensity decreased. The present blue shift is due to change of silicon nanocrystal structure at the surface.

Fluorine surface concentration change during the argon–oxygen ion treatment of porous silicon

The change in surface chemical contents and photoluminescence spectra of porous silicon are investigated after etching in argon plasma with oxygen admixture. Such a treatment leads to the saturation of dangling bonds by fluorine and to formation of silicon oxide on surfaces of quantum wires. After a preparation of porous layer, HF acid remnants inside voids become a source of fluorine, whose concentration grows accompanied by an increase in the greenish-blue photoluminescence band as well as red band broadening. It is shown that the surface fluorination does not influence the laser-irradiation-induced degradation of porous silicon photoluminescence.