Electrical Properties of Porous Silicon

The focus of this section is charge transport in PS, and electrical properties such as resistivity, carrier mobility, capacitance and photoconductivity are discussed. 

The measurement of properties such as the resistivity or dielectric constant of PS requires some kind of contact with the PS layer. Evaporation of a metal onto the PS film-covered silicon sample produces a metal/PS/Si sandwich, which behaves like an MIS structure with an imperfect insulator. Such sandwich structures usually exhibit a rectifying behavior, which has to be taken into account when determining the resistivity [Si3, Bel4]. This can be circumvented by four-terminal measurements of free-standing PS films, but for such contacts the applied electric field has to be limited to rather small values to avoid undesirable heating effects. An electrolytic contact can also be used to probe PS films, but the interpretation of the results is more complicated, because it is difficult to distinguish between ionic and electronic contributions to the measured conductivity. The electrolyte in the porous matrix may short-circuit the silicon filaments, and wetting of PS in- 

The conductivity of porous structures depends on the size of the conducting filaments making up the silicon skeleton [An5] and will therefore be discussed for each of the three size regimes separately. 

For a homogeneous porous layer a specific conductivity a can be defined  

According to the macropore formation mechanisms, as discussed in Section 9.1, the pore wall thickness of PS films formed on p-type substrates is always less than twice the SCR width. The conductivity of such a macroporous silicon film is therefore sensitive to the width of the surface depletion layer, which itself depends on the type and density of the surface charges present. For n-type substrates the pore spacing may become much more than twice the SCR width. In the latter case and for macro PS films that have been heavily doped after electrochemical formation, the effect of the surface depletion layer becomes negligible and the conductivity is determined by the geometry of the sample only. The conductivity parallel to the pores is then the bulk conductivity of the substrate times 1 -p, where p is the porosity. 

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Gokama A, Bhave TM, Bhoraskar SV, Kanjilal D (1999) Effect of swift high energy phosphorous ions on the optical and electrical properties of porous silicon. Nucl Instrum Methods Phys Res B 156 100-104... 

Attempts on Classification of Electrical Properties of Porous Silicon... 

Mikrajuddin, Shi FG, Okuyama K (2001) Temperature-dependent electrical conduction in porous silicon Non-Arrhenius behavior. Europhys Lett 54 234 Parkutik VP (1996) Residual electrolyte as a factor influencing the electrical properties of porous silicon. Thin Solid Films 276 195... 

Zhang L, Coffer JL, Gnade BE, DaXue X, Pinizzotto RF (1995) Effects of local ambient atmosphere on the stability of electroluminescent porous silicon diodes. J Appl Phys 77 5936 Zimin SP (2000) Classification of electrical properties of porous silicon. Semiconductors 34 353 Zimin SP (2006) Hopping conductivity in low-porosity mesoporous silicon formed on p -Si -B. Semiconductors 40(11) 1350... 

Anderson RC, Muller RS, Tobias CW (1991) Investigation of electrical properties of porous silicon. J Electrochem Soc 138 3406-3411... 

Arenas MC, Hu H, Rio JA et al (2006) Electrical properties of porous silicon/polypyrrole heterojunctions. Sol Energy Mater Sol Cells 90 2413-2420... 

Simons AJ, Cox TI, Uren MJ et al (1995) The electrical properties of porous silicon produced from n + silicon substrates. Thin Solid Films 255 12-15 Skryshevsky VA, Strikha VI, Mamikin AV et al (1998) Availability of current -voltage characteristics for porous silicon gas sensors, Discrete gas sensor. Paper presented at eorosensors XII13-16 Sept 277-280... 

Weiying O, Lei Z, Hongwei D, Jun Z, Wenjing W (2011) Optical and electrical properties of porous silicon layer formed on textured surface by electrochemical etching. J Semicond 32 1-4... 

Endres HE, Hartinger R, Schwaiger M, Gmelch G, Roth M (1999) A capacitive CO sensor system with suppression of the hunudity interference. Sens Actuators B 57(l-3) 83-87 Erdamar O, BUen B, Skarlatos Y, Aktas G, Ind MN (2007) Effects of humidity and acetone on the optical and electrical properties of porous silicon nanostructures. Physica Status Sohdi C 4 601-603 Fiiijes P, KovScs A, Diicso Cs, Adam M, Muller B, Mescheder U (2003) Porous sihcon-based humidity sensor with interdigital electrodes and internal heaters. Sens Actuators B 95 140-144 Goeders KM, Colton JS, Bottomley LA (2008) Microcantilevers sensing chemical interactions via mechanical motion. Chem Rev 108 522-542... 

L.T. Canham (Ed.), Properties of Porous Silicon, INSPEC The Institution of Electrical Engineers, London, 1997. 

Recent work by Mikulec et al. [117] has exploited an unusual property of porous silicon and used this material as an explosive matrix for atomic emission spectroscopy. Freshly prepared, hydride-terminated substrates soaked in aqueous solutions of Gd(N03)3 were detonated with mechanical or electrical triggers in a flashy, exothermic reaction not unlike the combustion of black powder (Figure 16.17). The estimated high ( 2000 K) local temperature created by the explosion was employed to generate emission spectra for alkali metals and heavy metals deposited upon the substrates from solution or suspension. Detonation was completed for a range of porous specimens and did not depend upon either the crystalline identity of the precursor or the morphology of the etched material however, oxidized substrates exhibited a lesser propensity to explode. The intensity of the explosion was... 

Boarino L, Borini S, Amato G (2009) Electrical properties of mesoporous silicon from a surface effect to coulomb blockade and more. J Electrochem Soc 156(12) K223-K226 Canham LT (1990) Siheon quantum wire array fabrication by electrochemical and chemical dissoluhon of waters. Appl Phys. Lett 57(10) 1046-1048 Canham LT (1997) Properties of porous siheon, EMIS datareview series no 18. lEE Press, London Canham LT, Houlton MR, Leong WY, Keen JM (1991) Atmospheric impregnation of porous siheon. J Appl Phys 70(1) 422-431... 

Canham LT (1997) Biomedical applications of porous silicon. In Canham LT (ed) Properties of porous silicon, vol 18, EMIS datareviews. Short Run Press, London, pp 12-22 Canham LT, Reeves CL (1996) Apatite nucleation on low porosity silicon in acellular simulated body fluids. In Cotell CM, Meyer AE, Gorbatkin SM, Grobe GL (eds) Thin films and surfaces for bioactivity and biomedical applications, vol 414, Materials research society symposium proceedings. Materials Research Society, Pittsburgh, pp 189-194 Canham LT, Newey JP, Reeves CL, Houlton MR, Loni A, Simmons AJ, Cox T1 (1996a) The effects of DC electric currents on the in-vitro calcification of bioactive Si wafers. Adv Mater 8(10) 847-849... 

The early research on the electrical transport properties of porous silicon carried out in the 1980s revealed that the resistivity of the porous silicon layer was a few orders of magnitude higher than the original substrate (Beale et al. 1985). While quantum confinement model has been successfully used to explain the luminescence properties of PS, applying it to explain the transport properties of PS has... 

Bouaicha M, Khardani M, Bessais B (2006) Correlation of electrical conductivity and photoluminescence in nanoporous silicon. Mater Sci Eng C 26 486 Bouaicha M, Khardani M, Bessais B (2008) Evaluation of the electrical conductivity of nano-porous silicon from photoluminescence and particle size distribution. Mater Sci Eng B 147 235 Canham LT (ed) (1997) Properties of Porous Silicon. lEE INSPEC, The Institution of Electrical Engineers, London... 

Electrical Transport in Porous Silicon ), and mechanical behavior ( Mechanical Properties of Porous Silicon ). 

Bsiesy A, Vial JC, Gaspard F et al (1991) Photoluminescence of high porosity and of electrochem-ically oxidized porous silicon layers. Surf Sci 254 195-200 Canham L (ed) (1997) Properties of porous silicon. INSPEC - The Institution of Electrical... 

Qiu T, Wu XL, Siu GG, Chu PK (2005) Self-assembled growth and green emission of gold nano whiskers. Appl Phys Lett 87 223115-1-223115-3 Qu Y, Liao L, Li Y, Zhang H, Huang Y, Duan X (2009) Electrically conductive and optically active porous silicon nanowires. Nano Lett 9(12) 4539 543 Qu Y, Zhong X, Li Y, Liao L, Huang Y, Duan X (2010) Photocatalytic properties of porous silicon nanowires. J Mater Chem 20(18) 3590-3594... 

Example of high-temperature treatment of mesoporous silicon into reorganized macropore-size voids can be seen in Fig. 1 (Kim et al. 2006). In this case porous silicon free-standing film serves as a template layer for epitaxial silicon growth, where reorganization controls surface closure of pores and reduction of stacking faults. 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 (Martini et al. 2012). 

Lin JC, Tsai WC, Lee WS (2006) The improved electrical contact between a metal and porous silicon by deposition using a supercritical fluid. Nanotechnology 17(12) 2968 Loni A (1997) Capping of porous silicon. In Canham LT (ed) Properties of porous silicon. lEE Press, London, pp 51-58... 

Yarkin DG (2003) Impedance of humidity sensitive metal/porous silicon/n-Si structures. Sens Actuators A 107 1-6 Yeh Y, Tseng T, Chang D (1989) Electrical properties of porous titania ceramic humidity sensors. J Am Ceram Soc 72 1472-1475... 

Nickel-mesoporous silicon structures are of considerable industrial interest for various applications. Anisotropy of magnetic properties of the nickel nanowires inside porous silicon conditioned by their high aspect ratio is applicable for the magnetic store production [1], Moreover, these structures offer much promise for the rectenna (a special type of antenna that is used to directly convert microwave energy into DC electricity) fabrication. So, it is of value to study in detail the process of the nickel electrodeposition into pores of porous silicon and elaborate control methods for pore filling with metal. 

A.O. Konstantinov, C.I. Harris and E. Janzen, Electrical properties and formation mechanism of porous silicon carbide, Appl. Phys. Lett., 65, 2699-2701 (1994). 

The future development of porous silicon (PS)-based optoelectronic devices depends on a proper understanding of electrical transport properties of the PS material. Electrical transport in PS is influenced not only by each step of processing and fabrication methods but also by the properties of the initial base substrate. This chapter endeavors to chronologically document how the knowledge base on the nature of carrier transport in PS and the factors governing the electrical properties has evolved over the past years. The topics covered include the proposed electrical transport models including those based on effective medium theories, studies on contacts, studies on physical factors influencing electrical transport, anisotropy in electrical transport, and attempts to classify the PS material. 

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