Porous silicon transition layer

A common way to find out the nature of ohmic contact to semiconductor is to measure the value of the specific contact resistance, pc (G cm ). Zimin etal. (1995), Zimin and Komarov (1998) measured the transition resistivity of the PS surfaces prepared from both p-type and n-type sihcon wafers with Al contact. Specific contact resistance of Al and Ni to p-type PS (55 % porosity) was reported by Kanungo and co-workers (Kanungo et al. 2009a Kanungo et al. 2006). Maji et al. reported the same for Al contact to macroporous silicon (2010). P. Vinod (2005,2009,2013) studied silver ohmic contact to p-type porous silicon by quantitative measurements of the specific contact resistance. Table 2 gives the summary of the reported work on specific contact resistance/transition-specific resistivity measurements. A separate chapter in this handbook Electrical Transport in Porous Silicon reviews the various factors that influence the resistivity of the porous silicon layer itself. 

Recent developments such as fast phonon-less transitions from carbon-terminated nanocrystals (Dohnalova et al. 2013), fast direct bandgap transitions (Prokofiev et al. 2009 de Boer et al. 2010), and very high values of luminescence quantum efficiencies of silicon nanocrystals in layers (in porous silicon, 23 % (Gelloz et al. 2005 Gelloz and Koshida 2005), and in other assemblies, 18-100 % (Ledoux et al. 2000) and 60 % (Jurbergs et al. 2006)) show that the luminescence of nanocrystalline silicon is progressively paving its way toward applications. 

In Kuzma-Filipek et al. (2009), the authors show an example of effective gettering by means of electrochemically fabricated multilayer of porous silicon etched into UMG Si substrates, intrinsically contaminated with transition metals impurities. The test structures consisted of a 15-layer stack of a total thickness of 1,300 nm on top of which 300 nm epitaxial silicon was grown by CVD. The structure was exposed to high-temperature treatment and the metal trapping effect was monitored by... 

Crystallized silicon is very nonreactive and requires extremely high temperatures to become reactive. It is also known to be a nonbiocompatible material with very poor hemocompatibility [9]. However, in 1995, Canham [10] demonstrated the bioactivity of pSi layers in simulated body fluids (SBFs). Here, the term bioactive refers to silicon as a biomaterial, which is deflned as a nonviable material intended to interact with biological systems when used in a medical device. As noted by Canham, the transition of silicon to a bioactive state via the introduction of pores is consistent with the fact that aU other natural biological materials are porous [77]. In Canham s study, 1 gm-thick pSi layers were incubated in various SBFs for periods ranging from 6h to 6 weeks. While the highly porous Si (porosity >70%) dissolved in aU SBFs tested, the silicon with medium porosity (<70%) was slowly biodegradable. Similar to solid silicon, very low-porosity silicon was shown to be bioinert Thus, porosity is directly related to bioactivity. 

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