Evaluation of mesoporous silicon thermal conductivity by electrothermal finite element simulation (original) (raw)
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Microelectronics Journal, 1999
Recently measured low thermal conductivity of as-prepared and slightly oxidized meso-porous silicon (meso-PS) offers new possibility to apply this promising material for thermal isolation in microsensors and microsystems. We report here a theoretical model describing specific mechanisms of heat transport in as-prepared and oxidized meso-PS. The model is in good agreement with experimental data obtained earlier.
Thermal conductivity of thick meso-porous silicon layers by micro-Raman scattering
Journal of Applied Physics, 1999
We report here a theoretical model describing specific mechanisms of heat transport in as-prepared and oxidized meso-porous silicon layers. The model is in good agreement with experimental measurements performed by micro-Raman scattering on the layers surface. For the first time, thermal conductivity inhomogeneity along the porous layer thickness of 100 m is studied. Direct correlation between the thermal conductivity and morphology variations along the layer thickness is brought to the fore. A new approach to estimate local porosity of the porous layers based on thermal conductivity and Si nanocrystallite size measurements is also proposed.
Thermal conductivity measurement of porous silicon by the pulsed-photothermal method
Journal of Physics D: Applied Physics, 2011
Thermal properties of two types of porous silicon are studied using the pulsed-photothermal method (PPT). This method is based on a pulsed-laser source in the nanosecond regime. A 1D analytical model is coupled with the PPT technique in order to determine thermal properties of the studied samples (thermal conductivity and volumetric heat capacity).
Thermal conductivity across nanostructured porous silicon films
Journal of Physics: Conference Series, 2007
This paper models the effect of pore size, pore arrangement and porosity on room temperature thermal conductivity across low porosity meso-porous silicon (meso-PS) films known as n+ and p+ type PS. Whereas the meso-PS films are simulated using a threedimensional (3D) pore network generator, the heat conduction is modeled using the Monte Carlo method (MCM) recently developed for simulating steady-state phonon transport in submicron structures. The simulations show that (i) the thermal conductivity across mesoporous films decreases when the pore size decreases or the porosity increases, in accordance with past studies. (ii) The thermal conductivity of n+ type pore network is always greater than that of p+ type due to the difference in pore morphology. Finally, the simulations corresponding to p+ type pore network are shown in good agreement with existing experimental data for low porosity p+ type PS. Such comparison confirms the validity of the current 3D modeling.
A Phenomenological Study of Pore-Size Dependent Thermal Conductivity of Porous Silicon
Acta Applicandae Mathematicae, 2012
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.
Journal of Applied Physics, 2020
Irradiating porous silicon is expected to reduce thermal conductivity without altering the porous structure and can be studied by optical techniques provided optical properties can be established reliably. Toward this end, meso-porous silicon (PSi), with a porosity of 56%, was prepared from p + Si wafer (0.01-0.02 .cm-1 resistivity) and was partially amorphized by irradiation in the electronic regime with 129 Xe ions at two different energies (29 MeV and 91 MeV) and five fluences ranging from 10 12 cm-2 to 3.10 13 cm-2. The PSi structure is monitored by scanning electron microscopy. High-resolution transmission electron microscopy shows that the amorphous phase is homogeneous in volume and that there is no formation of amorphous-crystalline core-shell structures. An agreement is found between the thermal conductivity results obtained with micro-Raman thermometry, which is an optical contactless technique heating the sample in the depth, and scanning thermal microscopy, which is an electrical technique heating the sample by contact at the sample surface. A linear relation is established between the effective thermal conductivity and the amorphous fraction, predicting the thermal conductivity of fully-amorphous porous Si below 1 W.m-1 .K-1. The obtained values are comparable to that of SiO2, reduced by a factor 6 in comparison to non-irradiated porous samples (~6.5 W.m-1 .K-1) and smaller than bulk silicon by more than two orders of magnitude.
Monte Carlo simulation of cross-plane thermal conductivity of nanostructured porous silicon films
Journal of Applied Physics, 2008
This paper presents a Monte Carlo ͑MC͒ modeling of heat conduction in heavily doped ͑p + and n + ͒ porous silicon ͑PS͒ films known as mesoporous silicon ͑meso-PS͒. A three-dimensional pore network generator is developed to better reproduce the structure of low porosity ͑f v Ͻ 50% ͒ meso-PS. The submicron scale heat conduction modeled by the Boltzman transport equation is simulated using the MC method in which the nonlinear phonon dispersion curves of bulk silicon and the phonon lifetime dependent on temperature, frequency, and polarization are taken into account. The proposed method has been applied to predict the effect of the porosity ͑10%-47%͒, pore sizes ͑10-20 nm͒, pore arrangement ͑p + -and n + -type͒, temperature ͑50-500 K͒, and film thickness ͑50 nm-1 m͒ on the cross-plane thermal conductivity of meso-PS films. Moreover, the simulation results enable to deduce the scattering mean free path ͑MFP͒ of phonons in the PS and the scattering MFP due to phonon-pore wall interaction. At room temperature, the thermal conductivity of meso-PS is shown one to two orders of magnitude smaller than that of bulk silicon. A drastic simplification of the phonon dispersion curves and phonon MFP, such as in the Debey approximation, results in an overestimation ͑by about three times͒ of the thermal conductivity of meso-PS. The thermal conductivity decreases when the pore size decreases or the porosity increases. For a given porosity and pore size, the thermal conductivity of doped p + -type PS is much smaller than that of doped n + -type PS. Finally, the simulations of thermal conductivity of doped p + -type PS are shown in good agreement with available experimental data which confirms the validity of the current modeling.