An alternative approach to understand the photoluminescence and the photoluminescence peak shift with excitation in porous silicon (original) (raw)
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Correlation of Photoluminescence and Optical Absorption Spectra of Porous Silicon
2000
Using a quantum confinement based-PL model, PS was modelled as a mixture of Quantum Dots (QDs) and Quantum Wires (QWs) having different concentrations and sizes. It was shown that in the optical absorption edge the PL peak energy and the Optical Absorption (OA) exhibit the same trend, depending on preparation conditions. The spectral behaviours of PL and OA are analysed and correlated throughout the shapes and the size distribution of the nanocrystallites forming PS. Using the quantum confinement formalism, the value of the effective band-gap energy determined from the lowest PL energy almost corresponds to that estimated from the optical absorption coefficient. These results suggest that the lowest radiative transition between the valence band and the conduction band corresponds to the largest luminescent wires, and that the radiative recombination process leading to the PL emission occurs in the c-Si crystallite core.
Correlation of photoluminescence spectra and structure of porous silicon
Semiconductor Science and Technology, 1996
Porous silicon (PS) layers emitting red photoluminescence (PL) have been prepared by anodization of p-type (100) monocrystalline silicon substrate in aqueous HF solutions. PS layers oxidized in free air exhibit under UV photoirradiation an intense yellow-orange PL, whilst as-prepared samples emit red PL. Our aim is to explain the PL behaviour and its origin in both unetched and HF etched as-prepared and oxidized PS layers according to calculated PL based on quantum confinement formalism and to infrared spectroscopy (IRS). It was found that the PL behaviour is associated with a quantum size effect and concentration change in quantum dots and wires. It was observed that HF etching of oxidized PS may induce a preponderance of dots or wires in the PS structure, depending on the oxidation degree, and produce a PL blueshift or redshift respectively. By correlating PL spectra of unetched and HF-etched oxidized PS, we found that highly oxidized PS transforms into an SiO 2 matrix in which photoluminescent nanocrystalline Si quantum dots are embedded.
Relation between electroluminescence and photoluminescence in porous silicon
Materials Science and Engineering: B, 2000
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.
Journal of Physics and Chemistry of Solids, 2000
Photoluminescence (PL) and photoluminescence excitation spectra research, as well as secondary ion mass spectroscopy and infrared vibration spectra measurements, were used for the investigation of PL excitation mechanism of porous silicon. It is shown that there are two types of porous silicon PL excitation spectra: one that consists of visible and ultraviolet bands and one that contains only an ultraviolet one. The different dependencies of intensity of each excitation band upon anodization regimes, as well as ageing and thermal treatment, were observed. Two excitation channels have been shown in porous silicon. The visible PL excitation band at 300 K has been attributed to light absorption of some species on the Si wire surface. The nature of ultraviolet excitation band is also discussed.
Effect of Silicon Crystal Size on Photoluminescence Appearance in Porous Silicon
ISRN Nanotechnology, 2011
The photoluminescence (PL) study in porous silicon (PS) with decreasing Si crystallites size among the pores was reported. The PL appearance is attributed to electronic confinement in columnar-like (or dotlike) structures of porous silicon. Three different pore diameter PS samples were prepared by electrochemical etching in HF-based solutions. Changes in porous silicon and Si crystallite size were studied by observing an asymmetric broadening and shift of the optical silicon phonons in Raman scattering. Fourier transform infrared spectroscopy (FTIR) was used to study the role of siloxene or other molecular species, for example, SiH x in the luminescence mechanism. This mechanism was further studied by thermal annealing of PS at different temperatures. The PL of PS sample annealed at ≥300 • C for 1 hr shows that trap electronic states appear in the energy gap of the smaller nano-crystal when Si-O-Si bonds are formed. From the observation of PL, Raman, and FTIR spectroscopy, the origin of PL in terms of intrinsic and extrinsic properties of nanocrystalline silicon was discussed.
Origin of the photoluminescence shifts in porous silicon
The European Physical Journal Applied Physics, 1998
The origin of the photoluminescence (PL) shifts in Porous Silicon (PS) is discussed according to a quantum confinement-based model, in which we modelize the PS layer as a mixture of quantum dots and wires. It was shown that a PL blueshift or redshift may occur during laser irradiation of PS, depending on preparation conditions. No PL shift was observed for some PS samples, even after a long ageing in air, due to the presence of an amorphous silicon phase detected from Raman spectroscopy measurements. It was found that the presence of the amorphous phase plays an important role in the PL behaviour of oxidised PS.
The effect of electric field on the photoluminescence and absorption spectra of porous silicon
Thin Solid Films, 2000
The effect of electric ®eld on the photoluminescence and absorption spectra of porous silicon were investigated. An electric ®eld applied perpendicular to the porous silicon growth direction shows a red shift in the photoluminescence peak energy and quenching of the photoluminescence intensity, whereas an electric ®eld applied parallel to the growth direction shows photoluminescence quenching, but no clear indication of red shift. The absorption spectra also show a red shift of the absorption edge together with an increase in the absorption coef®cient when an electric is ®eld applied perpendicular to the porous silicon growth direction. The results are qualitatively similar to the quantum con®ned Stark effect, and provide additional support for quantum size effect as the mechanism of light emission in porous silicon. q
Journal of Applied Physics, 2000
Porous silicon thin films created under laser illumination in fluoride solutions without biasing have been studied by a variety of techniques to investigate the film structure and photoluminescence (PL). The use of ultrathin silicon wafers allows us to perform plan view transmission electron microscopy studies without recourse to thinning procedures that might adversely affect the film structure. Supercritically dried samples are compared to air dried samples and clearly demonstrate the deleterious effects of air drying on film structure. PL studies were performed (a) while the sample is submerged in aqueous HF, (b) in Ar after rinsing in ethanol, and (c) in air after rinsing in ethanol. The wavelength of light used to fabricate the film is found to correlate strongly with the peak PL wavelength when measured in solution. Little correlation is found in Ar or in air. Exposure to air can change the PL spectrum dramatically on a time scale of just seconds. We demonstrate that samples can exhibit essentially identical PL spectra in one medium but have spectra that differ from one another when the samples are placed in a different medium. The PL results indicate that band-to-band recombination cannot explain photon emission under all circumstances, and that surface states must also be involved in radiative processes under those conditions in which the bands are sufficiently separated to allow for the appearance of gap states.
Effect of the desorption process on photoluminescence excitation spectra of porous silicon
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.