Influence of applied current density on the nanostructural and light emitting properties of n-type porous silicon (original) (raw)
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Study of Photoluminescence Behaviour of Porous Silicon Samples Prepared at 20 mA Current Density
2013
Porous silicon (PS) is considered to be composed either of spherical shaped interconnected silicon quantum dots or combination of quantum dots and columns. During the last decades, there has been a rapid research to introduce porous silicon [1] in optoelectronics and medical field [2]. Every field of applications, require an optimized PS structures under experimental conditions. As PS-based solar cells require thin and highly porous structures [3] and the drug loaded in PS depends on the properties of both the micro particles and the loaded substances [2] therefore, it is the need to study the distribution of crystallites size in a PS system through existing theoretical models. Therefore, the main objectives of present work are to determine the average diameter of the crystallites from extend of the photoluminescence (PL) spectra broadening and to verify the results and prediction of Islam-Kumar model, explaining the shape of the PL spectra. As PL signal of PS at room temperature is...
Malaysian Journal of Fundamental and Applied Sciences
Achieving high quality porous silicon (PSi) materials with desired porosity remains challenging. Three good qualities of PSi samples are prepared by Photo electro-chemically etching a piece of n-type Si inside the solution of 20 M HF, 10 M C2H5OH and 10 M H2O2 at fixed etching time duration (30 min) and varying current density (15 mA/cm2, 30 mA/cm2 and 45 mA/cm2). As-prepared sample morphologies are characterized via scanning electron microscopy (SEM) and atomic force microscopy (AFM). The gravimetric method is used to estimate the thickness and porosity of the prepared samples. Current density (etching time) dependent morphologies, electronic bandgap and room temperature photoluminescence (PL) properties of such PSi nanostructures are evaluated. These PSi structures revealed enhanced rectifying characteristics with increasing current density.
Correlation of optical and structural properties of light emitting porous silicon
Applied Physics Letters, 1993
Microscopic structures of light emitting porous silicon layers have been studied. The samples prepared in an aqueous HF solution by anodizing p-type silicon substrates show a strong positional dependence of photoluminescence and Raman spectra. The photoluminescence peaks are broad around 1.8 eV, where the photoluminescence intensities are comparable to that of GaAs at 5 K. We have found from Raman studies showing two characteristic peaks at 500 and 520 cm−1 that microscopic structures reveal gradual changes from porous silicon to a mixture of polycrystalline and hydrogenated amorphous phases as the probing spot is moved to the edge of the sample. This is explained by the redeposition of silicon atoms on top of the porous silicon layers near the edge of the sample as a result of liquid flow caused by bubbles of hydrogen gas which was produced near the surface of the sample during the anodization process.
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.
Microelectronic Engineering
Photoluminescence properties and surface morphologies of porous silicon were investigated by controlling of etching times and applied current densities. FE-SEM image of porous silicon surface indicated that the porous silicon prepared at currents below 200 mA/cm 2 exhibited very stable and even surface. However the porous silicon prepared at currents above 300 mA/cm 2 displayed the cracked surface of porous silicon. This cracked surface was collapsed to give cracked domains at currents over 500 mA/cm 2 . Photoluminescence of porous silicon was investigated by controlling of etching times and applied current densities in the range from 50 to 900 s and from 50 to 800 mA/cm 2 , respectively. Photoluminescence intensity of porous silicon increased gradually during etching process, reached maximum, and then decreased as the etching time increased. Porous silicon showed the best photoluminescence efficiency was prepared at currents of 200 mA/cm 2 and etching time of 300 s.
Optical and microstructural investigations of porous silicon
Bulletin of Materials Science, 2005
Raman scattering and photoluminescence (PL) measurements on (100) oriented n-type crystalline silicon (c-Si) and porous silicon (PS) samples were carried out. PS samples were prepared by anodic etching of c-Si under the illumination of light for different etching times of 30, 60 and 90 min. Raman scattering from the optical phonon in PS showed the redshift of the phonon frequency, broadening and increased asymmetry of the Raman mode on increasing the etching time. Using the phonon confinement model, the average diameter of Si nanocrystallites has been estimated as 2⋅ ⋅9, 2⋅ ⋅6 and 2⋅ ⋅3 nm for 30, 60 and 90 min samples, respectively. Similar size of Si crystallites has been confirmed from the high resolution transmission electron microscopy (HRTEM). Using 2TO phonon mode intensity, we conjectured that the disordered Si region around the pores present in 30 min PS dissolved on etching for 90 min. The photoluminescence (PL) from PS increased in intensity and blue shifted with etching time from 2⋅ ⋅1-2⋅ ⋅3 eV. Blue shifting of PL is consistent with quantum confinement of electron in Si nanocrystallites and their sizes are estimated as 2⋅ ⋅4, 2⋅ ⋅3 and 2⋅ ⋅1 nm for 30, 60 and 90 min PS, respectively which are smaller than the Raman estimated sizes due to temperature effect. Unambiguous dominance of quantum confinement effect is reported in these PS samples.
Experimental study of n-type porous silicon obtained under illumination
Optik, 2018
Porous silicon (PS) has been prepared from n-type (100) silicon substrate by using electrochemical etching under He-Ne laser illumination. The PS was produced within several etching conditions. The morphological, structural and optical properties were studied by using atomic force microscopy (AFM), X-ray diffraction (XRD), Raman analysis, and reflectance measurements. Results show that the evolution of the obtained nanostructures is strongly related to anodization conditions. The optical analysis results show that a low reflectance was obtained for samples anodized by increasing current density. This is correlated to morphological results showing the strong dependence of the obtained nanoporous structure in terms of crystallites sizes and porosity, on the anodization conditions.
Porous silicon: material properties, visible photo- and electroluminescence
Applied Surface Science, 1993
Following the recent discovery of visible photo and electroluminescence of high-porosity porous silicon layers this paper presents a review of the most relevant results and models proposed to explain the phenomena. Porous silicon fabrication techniques are presented including some recommendations to allow a meaningful comparison of results obtained hy different laboratories. Recent results of pore size. surface area measurements. crystallographic structure determination and microstructure observations are discussed. Detailed studies of optical absorption coefficients of porous layers of different porosities are pt-esentetf. A clear upshift toward the visible range is explained by a quantum confinement model. Intense visible photoluminesccnce ol porous silicon layers is discussed on the ground of both quantum confinement and surface-controlled phenomena. The caaential role played by surface passivation, for efficient luminescence. is analysed. Reported results of visible electroluminescence during anodic oxidation of porous silicon layers and visible light emission from solid-state porous silicon dcviccs are reviewed.
Nanostructure and optical propertes of porous silicon layer
Maǧallaẗ ǧāmiʻaẗ kirkūk, 2015
In this paper nanostructures Porous silicon layers have been prepared by electrochemical etching (ECE) technique of (111) P-type silicon wafer with a solution Electrolytic HF: ethanol at a concentration of 1:2 with various anodization currents and etching time of 20 min. The morphological, structural and optical properties of nanostructure porous silicon were investigated by Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD) and Photoluminescence (PL) respectively. From AFM images, we found that the PS layer has sponge like structure, and average diameter of pore and thickness of PS layer increased with increasing of the anodization currents. X-ray diffraction show that the crystal size was reduced toward nanometric scale, and then a broadening of diffraction peaks (111) was observed. The band gap of the samples was measured through the photoluminescence (PL) peak.