Mechanical properties of sintered meso-porous silicon: A numerical model

Nanoscale Research Letters (Impact Factor: 2.78). 10/2012; 7(1):597. DOI: 10.1186/1556-276X-7-597
Source: PubMed


Because of its optical and electrical properties, large surfaces, and compatibility with standard silicon processes, porous silicon is a very interesting material in photovoltaic and microelectromechanical systems technology. In some applications, porous silicon is annealed at high temperature and, consequently, the cylindrical pores that are generated by anodization or stain etching reorganize into randomly distributed closed sphere-like pores. Although the design of devices which involve this material needs an accurate evaluation of its mechanical properties, only few researchers have studied the mechanical properties of porous silicon, and no data are nowadays available on the mechanical properties of sintered porous silicon. In this work we propose a finite element model to estimate the mechanical properties of sintered meso-porous silicon. The model has been employed to study the dependence of the Young's modulus and the shear modulus (upper and lower bounds) on the porosity for porosities between 0% to 40%. Interpolation functions for the Young's modulus and shear modulus have been obtained, and the results show good agreement with the data reported for other porous media. A Monte Carlo simulation has also been employed to study the effect of the actual microstructure on the mechanical properties.

Download full-text


Available from: J. Poortmans,
  • Source
    • "Thus, a rougher porous silicon template with a similar intrinsic stress is likely to have local concentrations of higher stress at the growth surface. Third, a thinner LPL with smaller pore size distribution (and possibly lower porosity [see Fig. 2(c)] is likely to be stiffer than a thicker LPL [31], [32]. A stiffer material with the same intrinsic stress will induce a lower amount of strain in the growing silicon epilayer. "
    [Show abstract] [Hide abstract]
    ABSTRACT: A porous silicon-based layer transfer process to pro-duce thin (30–50 μm) kerfless epitaxial foils (epifoils) is a promising approach toward high-efficiency solar cells. For high efficiencies, the epifoil must have high minority carrier lifetimes. The epifoil quality depends on the properties of the porous layer since it is the template for epitaxy. It is shown that by reducing the thickness of this layer and/or its porosity in the near-surface region, the near-surface void size is reduced to <65 nm and in certain cases achieve a 100 nm-thick void-free zone below the surface. Together with better void alignment, this allows for a smoother growth surface with a roughness of <3 A and reduced stress in the porous silicon. These improvements translate into significantly diminished epifoil crystal defect densities as low as ∼420 defects/cm 2 . Although epi-foils on very thin porous silicon were not detachable, a significant improvement in the lifetime (diffusion length) of safely detachable n-type epifoils from ∼85 (∼300 μm) to ∼195 μs (∼470 μm) at the injection level of 10 15 /cm 3 is achieved by tuning the porous silicon template. Lifetimes exceeding ∼350 μs have been achieved in the reference lithography-based epifoils, showing the potential for improvement in porous silicon-based epifoils.
    IEEE Journal of Photovoltaics 01/2014; 4. DOI:10.1109/JPHOTOV.2013.2282740 · 3.17 Impact Factor
  • Source
    • "Sintering controls also electrical properties of the porous layer, and the actual distribution of voids which is expected to play a role in the mechanical properties of porous silicon [16] . Fig 1. Reorganized porous structure due to high temperature treatment (1130˚C ) in H2 and atmospheric pressure chamber [14] Sintering is defined as the thermal treatment of porous or powder materials below their melting point (for silicon it is 1412°C) accompanied by structural changes. "
    [Show abstract] [Hide abstract]
    ABSTRACT: High surface area mesoporous silicon is prone to sintering, which can be an issue for some applications and be exploited for others. The mechanisms of silicon sintering, conditions that promote it, methods of characterizing, effects on properties, and potential uses are reviewed.
    Handbook of Porous Silicon, 01/2014: pages 1-11; , ISBN: 978-3-319-04508-5
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report on the epitaxial growth of Ge virtual substrates directly on Si (001) and on different porosity porous silicon (pSi) buffers. Obtained results indicate that Ge grown on low porosity (22%) pSi buffer has a better crystalline quality compared to Ge grown on bulk Si and on higher porosity buffers. This result is attributed to the compliant nature of pSi and to its reduced Young's modulus, which leads to plastic tensile deformation of the 22% porosity buffer under the in-plane tensile stress introduced by Ge lattice. The same result is not observed for higher porosity buffers, this effect being attributed to the higher buffer fragility. A low porosity pSi layer can hence be used as buffer for the growth of Ge on Si virtual substrates with reduced dislocation content and for the growth of Ge based devices or the successive integration of III-V semiconductors on Si.
    Applied Physics Letters 09/2014; 105(12):122104-122104-5. DOI:10.1063/1.4894863 · 3.30 Impact Factor