Conductivity Of Porous Silicon Research Articles

The EPR and Luminescence of Porous Silicon

The data on the EPR, photoluminescence (PL), and current transfer in porous silicon (PS) on KDB-0.3 and KES-0.01 Si, which was oxidized by 10-min isochronous thermal annealing in air at temperatures Tann from 20 to 900°C, as well as in HNO3, are presented in order to further clarify the nature of Pb centers of nonradiative recombination. The maximum PL quantum yield was observed during the chemical oxidation of PS on KDB-0.3 silicon. An anticorrelation of the PL and EPR intensities of Pb centers is observed in the range Tann = (20–300)°C. A nonmonotonic dependence of the EPR intensity of Pb centers on Tann with a minimum at approximately 700°C is revealed. The weak PL of PS with Tann of ~700°C accompanied by a minimum EPR signal from Pb centers means that other nonradiative-recombination centers arise after annealing. A decrease in the PS conductivity with an increase in Tann is associated with the decomposition of Si fibers in PS into small granules, through which discrete tunneling of current carriers occurs.

ЭПР и люминесценция пористого кремния

There are presented research data of ESR, photoluminescence (PL) and carrent transport in porous silicon (PS) on KDB-0.3 and KES-0.01 Si, oxidized by10 minute isochronous thermal annealing on air at temperatures Tann from 20°С to 900°С and also in HNO3 for the purpose of the further clearing of Pb - centres nature of no radiating recombination. Maximum quantum yield of PL was observed at chemical oxidation of the PS on silicon of KDB-0.3 mark.. Anticorrelation of PL and ESR intensities of Pb - centres in the range of Tann = (20-300) °С takes a place. . Nonmonotonic dependence of ESR intensity of Pb - centres vs Tann with a minimum nearby 700°С is found out. Weak PL in PS with Tann nearby 700°С at minimum of ESR of Pb - centres means occurrence with annealing of other no radiating recombination centres. Falling of conductivity of PS with growth of Tann is connected with disintegration of Si fibres in Ps on small granules through which there is a discrete tunneling of current carriers.

Pore-size dependence of the heat conduction in porous silicon and phonon spectral energy density analysis

Semiconductor devices made of silicon material have been widely used due to its excellent thermoelectrical properties. Here, the silicon material with aligned distributed rectangular-shaped holes is proposed for the manufacture of semiconductor device. Comprehensive understanding the heat conduction is of great significance to improve the efficiency of the thermoelectrical materials. This letter investigates the thermal conductivity of nanoscale porous silicon structures by adopting the nonequilibrium molecular dynamics method. The results demonstrate that the temperature is sensitive to the sizes of the rectangular-shaped holes. Additionally, it is found that the effective thermal conductivity significantly decreases with the increase of the dimensions of the holes. Our work reveals that the key to reduce the effective thermal conductivity is to disturb the distribution of heat flux. Furthermore, the phonon spectral energy density method is used to obtain the phonon dispersion and phonon energy in the frequency domain.

Effect of Long-Range Passivation of Impurity Atoms by Surface Dangling Bonds on the Conductivity of Porous Silicon

Effect of Long-Range Passivation of Impurity Atoms by Surface Dangling Bonds on the Conductivity of Porous Silicon

Features of Chemically Etched Porous Silicon

The paper describes a complex study of chemically etched porous silicon layers and the relationship between etching parameters and porous layer properties. We show that the conductivity of porous silicon is similar to that of amorphous silicon. Chemical etching allows creating porous layers with the same intensity of photoluminescence and absorption as for anodically etched porous silicon.

Amorphization and reduction of thermal conductivity in porous silicon by irradiation with swift heavy ions

In this article, we demonstrate that the thermal conductivity of nanostructured porous silicon is reduced by amorphization and also that this amorphous phase in porous silicon can be created by swift (high-energy) heavy ion irradiation. Porous silicon samples with 41%-75% porosity are irradiated with 110 MeV uranium ions at six different fluences. Structural characterisation by micro-Raman spectroscopy and SEM imaging show that swift heavy ion irradiation causes the creation of an amorphous phase in porous Si but without suppressing its porous structure. We demonstrate that the amorphization of porous silicon is caused by electronic-regime interactions, which is the first time such an effect is obtained in crystalline silicon with single-ion species. Furthermore, the impact on the thermal conductivity of porous silicon is studied by micro-Raman spectroscopy and scanning thermal microscopy. The creation of an amorphous phase in porous silicon leads to a reduction of its thermal conductivity, up to a factor of 3 compared to the non-irradiated sample. Therefore, this technique could be used to enhance the thermal insulation properties of porous Si. Finally, we show that this treatment can be combined with pre-oxidation at 300 °C, which is known to lower the thermal conductivity of porous Si, in order to obtain an even greater reduction.

Changes of Thermal Conductivity , Optical Conductivity and Electric Conductivity of Porous Silicon with Porosity

Changes of Thermal Conductivity , Optical Conductivity and Electric Conductivity of Porous Silicon with Porosity

A Phenomenological Study of Pore-Size Dependent Thermal Conductivity of Porous Silicon

A phonon-hydrodynamics approach is used to analyze the influence of porosity and of pore size on the reduction of the thermal conductivity in porous silicon. Different geometrical arrangements of the pores have been considered. For any given value of the porosity, the theoretical results show that for increasing Knudsen number (i.e., decreasing pore size) the effective thermal conductivity decreases whatever the geometrical arrangement of the pores is.

Pore-size dependence of the thermal conductivity of porous silicon: A phonon hydrodynamic approach

Phonon hydrodynamics is used to analyze the influence of porosity and of pore size on reduction in thermal conductivity in porous silicon, with respect to crystalline silicon. The expressions predict that the thermal conductivity is lower for higher porosity and for smaller pore radius, as a consequence of phonon ballistic effects. The theoretical results describe experimental data better than the assumption that they only depend on porosity.

Effect of thermal oxidation on charge carrier transport in nanostructured silicon

The effect of short-time annealing in air on the conductivity of porous silicon in two different directions (parallel and orthogonal to the sample surface) is studied. The samples under study are produced by electrochemical etching of single-crystal silicon wafers with (100)-oriented surfaces. It is found that thermal oxidation of the resulting porous silicon layers has different effects on the conductivity measured normally and parallel to the sample surface. For the oxidized samples, the conductivity in the direction orthogonal to the surface is noticeably higher than the conductivity in the direction parallel to the surface. The results are interpreted in the context of the model of charge carrier transport with consideration for potential barriers at the boundaries of silicon nanocrystals.

Low energy loss rf circuits on nanostructured porous silicon layers

AbstractWe present a work dealing with the study of thick porous silicon (PS) as insulating substrate for radio frequency (rf) circuits. Planar LC resonant circuits of 2 mm x 2 mm were designed on 100 µm thick PS layers for uses in 10 MHz to 1 GHz frequency range. The influence of PS electrical conductivity on the energy loss is determined using an original method based on experimental data combined with numerical simulations. We have clearly shown the increase of PS conductivity with the frequency due to hopping transport mechanisms in disordered materials. The contribution of the porous substrate to the energy loss is dominant for conductivities higher than 10–3 S/cm. Finally, the insertion of a SiO2 layer between an oxidized porous substrate and the integrated micro‐coil is suggested to optimize the quality factor of integrated rf resonnant circuits. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Application of scanning thermal microscopy for thermal conductivity measurements on meso-porous silicon thin films

A scanning thermal microscope (SThM) in the dc regime was used to study the thermal conductivity of homogeneous in-depth meso-porous silicon in the form of thin films on a monocrystalline silicon substrate. Measurements for different film porosities (30–80%) and thicknesses (100 nm–8 µm) were performed in order to estimate the influence of both layer porosity and thickness on the thermal conductivity values of porous silicon (PS). An analytical model predicting the SThM measurement in the case of ultra-thin monolayered samples was used to calibrate the technique, to analyse experimental data and to determine the thermal conductivity of meso-porous layers. Effective thermal conductivity of meso-PS films was found to decrease when the porosity increases. The effective thermal conductivities measured for thick porous layers (several µm) are in good accordance with those measured by micro-Raman-spectroscopy on bulk meso-PS samples. For submicrometric thicknesses (<1 µm), the effective thermal conductivity of layers decreases significantly with decreasing layer thickness due to the increased sensitivity of measurements to the thermal resistance of the film/substrate interface. An intrinsic thermal conductivity of PS was calculated independently of the film thickness and the values of interfacial thermal resistances were thus estimated. From the apparatus point of view, the results obtained show that the depth being sensed is of the order of a few micrometres for insulating materials and depends on the thermal conductivity of the films.

Properties of erbium silicate doped with chromium in porous silicon

The possible formation of chromium-doped erbium silicate Er2SiO5: Cr in thin layers of porous silicon is demonstrated. This paper reports on studies of the photoluminescence, electron paramagnetic resonance, and transverse current transport in porous silicon layers (with different chromium and erbium contents) grown on n-and p-silicon single crystals heavily doped with shallow impurities. The Er2SiO5: Cr phase with the photoluminescence maxima at approximately 1.3 and 1.5 μm manifests itself after high-temperature annealing at 1000°C. The introduction of erbium and annealing at 700°C increase the intensity of the red photoluminescence of porous silicon by several factors. The decrease in the electrical conductivity of porous silicon suggests the onset of the formation of erbium silicate. The current-voltage characteristics exhibit a nonlinear behavior with an exponential dependence of the current on the voltage due to the discrete electron tunneling. An electron paramagnetic resonance spectrum of P b centers in p-type heavily doped silicon is observed for the first time.

Laser local oxidation of porous silicon: a FTIR spectroscopy investigation

The local oxidation of porous silicon (PS), induced by a focused laser beam, could represent an alternative method for patterning PS through direct writing. Important phase changes take place on PS when irradiated by a focused laser beam and moreover a complete confinement of the oxidized areas can be achieved due to the very low thermal conductivity of PS. We present a detailed Fourier Transform InfraRed (FTIR) study of the irradiated areas to understand the degree of oxidation and the type of oxide obtained at different laser powers. An interpretation of the low wavenumber range, below 1300 cm -1 , in terms of Frohlich interactions will be discussed.

Space Charge Limited Current in Porous Silicon with traces of Nitrogen Dioxide

AbstractThe discovery of the steep increase of electrical conductivity in Porous Silicon (PS) samples in contact with Nitrogen Dioxide, NO2, opens the possibility to study the electrical conduction processes in nanostructured systems from a completely new point of view. The system undergoes a change of conductivity of 5 orders of magnitude when exposed to few ppm of NO2, whereas the free charge concentration increases by only one order of magnitude in the same pressure range. Upon NO2 exposure the system transition from an “insulator-like” to a “semiconductor-like” behaviour can be studied by means of several techniques. In this paper, the results from a Space Charge Limited Current (SCLC) study unambiguously demonstrate the change of the charging status of defects upon NO2exposure, and explain some “exotic” effects recently reported.

Specific features of electrical transport in anisotropically nanostructured silicon

Electrical transport in layers of porous silicon obtained by electrochemical etching of (110)-oriented single-crystal silicon wafers of p type was studied. It was found that the lateral conductivity and photoconductivity of the layers along the \([1\bar 10]\) crystallographic axis substantially exceed those along the [001] axis. The results obtained are explained in terms of the effective-medium model, which takes into account the presence of potential barriers at boundaries of anisotropically shaped silicon nanocrystals. The exponential dependence of the conductivity of porous silicon on the square root of the applied voltage is interpreted in terms of the Poole-Frenkel effect.

Tensoresistive effect in porous silicon layers with different morphology

The effect of elastic flexural strain on electrical conductivity of porous silicon with different pore morphology and different properties of depletion regions around the pores is studied. Porous layers are formed using anodic electrochemical etching of the p-and n-Si wafers and have a porosity of 5–68%. It is shown that specific features of variations in electrical conductivity of porous silicon under the effect of deformation depend on the structural characteristics of the porous material. In order to explain the results obtained, various physical models of the charge-carrier transport in porous silicon are used.

Thermal Conductivity of Porous Silicon Evaluated from Phase Characteristics of Photoacoustic Spectroscopy

ABSTRACTPorous silicon (PS), well known as a visible luminescent material, has been revealed to be an attractive candidate for an ultrasonic emitter recently. Since the ultrasonic emission is based on a thermal process it is important to evaluate thermal properties of PS. We then evaluated the thermal conductivity of PS from the phase delay in a photoacoustic (PA) signal. We report the dependence of thermal conductivity on anodization time in forming PS.

Thermal properties of suspended porous silicon micro-hotplates for sensor applications

In this work, the thermal properties of suspended porous silicon (PS) micro-hotplates are investigated. The micro-hotplates are fabricated by a novel technique, based on the isotropic etching of silicon under a PS layer, in a high-density plasma reactor. Suspended PS micro-hotplates with integrated heaters have been fabricated and characterized. Both the supporting beams and the rim surrounding the membrane are made of PS. This results in minimization of the thermal losses to the substrate. Very high local temperatures on the micro-hotplates (higher than 600°C) with very low power consumption (only a few tens of mW) have been obtained, due to the very low thermal conductivity of PS, which is comparable to that of thermal oxide and it is much lower than that of silicon nitride, typically used for thermal sensor applications.

Lateral structuring of porous silicon: application to waveguides

The problem of lateral definition of waveguides and photonic structures has been tackled by means of direct laser scribing on porous silicon (PS). The low thermal conductivity of PS allows for local oxidation and even the complete ablation of the material with laser power of a few mW. The buried Laser Local Oxidized (LaLOx) method exhibits great versatility and efficiency in achieving lateral light confinement in waveguides.