Porous Silicon Science and Technology (original) (raw)

Some new results in porous silicon

Bulletin of Materials Science, 1994

Efforts have been made to see the effect of some standard microelectronic processing steps on porous silicon. Our diffusion experiments for making p-n junctions confirm that this material can withstand high temperatures of the order of 800°C to 1000°C. A new technique for photolithography has been suggested to obtain porous silicon in selected areas. Etch stop method to control the thickness of the porous layer and an organic protective layer for porous silicon have also been suggested. Models proposed by other workers to explain luminescence in porous silicon are not sufficient to explain many experimental observations. A hybrid model is suggested.

Porous silicon: A silicon structure with new optical properties

Progress in Quantum Electronics, 1994

The recent discovery that highly porous silicon (PS), obtained by electrochemically etching a silicon wafer, could efficiently emit visible light at room temperature, has stimulated a considerable amount of experimental and theoretical research. The technological interest of this material arises from the potential applicability in the production of silicon-based optoelectronic devices. In this article we present the current understanding of the microstructure of PS in relation to the outstanding optical properties, formerly unexpected, in silicon structures. We also review the theoretical models proposed to explain the luminescence in PS and address the relevant aspects of these studies in view of the current progress toward nanostructure technology.

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.

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.

Morphological and Optical Properties of Porous Silicon

Engineering and Technology Journal

In this work photo-electrochemical etching was used to synthesize uniform and non-uniform macro porous silicon from n-type with orientation (100). Specimens were anodized in a sol of 25% HF: C2H2OH at 1:1 rate. Morphology and porosity of the samples were studied. Optical characteristics (reflection and photoluminescence) of PS samples by changing current density (10, 12, 14 and 16 mA/cm 2) for fixed etching time (8min) and power density (17mW/cm 2) by using red laser illumination wavelength (645nm) were investigated. Porous silicon samples imaged via scanning electron microscope (SEM), which showed the topography of silicon surface and pores distribution.

Mechanical, Optical and Electrical Properties of Porous Silicon Prepared under Clean Conditions

Optical Properties of Low Dimensional Silicon Structures, 1993

We present the mechanical, electrical and optical properties of light emitting porous silicon (LEPOS) prepared under clean conditions. It was found that the asanodised layers are in a compressive state, and that after annealing the stress changes and plastic deformation takes place. The film resistivities are greater than 10 7 il-cm. Photoluminescence stability from LEPOS is demonstrated on the scale of months. Finally, we present our measurements of the reflectance of porous Si on crystalline Si and show that it is very low over a wide spectral range.

Porous silicon as a promising material for photonics

International Journal of Nanotechnology, 2011

Electrochemical etching-a usual technique in nanotechnology-creates porous silicon with novel and useful properties. The considerable and controllable changes in the electronic structure and refractive index of porous silicon make it a promising material for photonics in comparison with bulk silicon. In this paper, we review as well as report on some interesting and unique properties of porous silicon material. In studying porous silicon as a low-dimensional material, we focus on the effect of the surface passivation of silicon nanocrystals on photoluminescence characteristics of such zero-dimensional crystals. As an optical material, we demonstrate the fabrication method and optical properties of the planar waveguide as well as the active waveguide and optical interference filters operated in infrared wavelengths. In addition, we investigated the effect of energy transfer from silicon nanocrystals to erbium ions in the erbium-doped porous silicon waveguide and also elaborate on the origins of the difference between the reflectivity spectra from fabricated filters and that of the simulation program.

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.

Optical properties of porous silicon thin films

Journal of Molecular Structure, 1999

Spectroellipsometrical (SE) investigations in 1.5-4.0 eV spectral range were done for optical characterization of porous silicon (PS) thin films. A mixing of a crystalline silicon and amorphous silicon with voids using Effective Medium Approximation [D.E. Aspnes, Phys. Rev. B 27 (1983) 985] is used to calculated the refraction index (n) and the absorption constant (k) of the PS layers. Measurements were done on PS obtained electrochemically on p ϩ silicon substrates. From the dispersion spectra of the refractive index, using the Wemple DiDomenico model [S.H. Wemple, M. DiDomenico Jr., Phys. Rev. B 3 (1971) 41338], the values for optical band gap, energy oscillator and dispersion energy for PS (model's parameters introduced by Wemple) are evaluated.