Silicon defects

MINDO/3 and MNDO, utilized widely by chemists for molecular problems, were introduced to silicon dioxide defect physics by Edwards and Fowler (1985) and to silicon defect physics by DeLeo et al. (1984b). They have since been applied to many defect problems in these systems, with considerable success. Both can be used in restricted or unrestricted Hartree-Fock form. MNDO has a practical advantage in that it is formulated in a way that all parameters are associated with particular atoms in effect,... 

Based on this model, the hyperfine spectra for the defect can be related to the s- and p- components of the wavefunction (Stutzmann and Biegelsen, 1988). Table 4.1 shows the results and compares them with the silicon defects which are known to be of the dangling bond type in other materials. An sp dangling bond has J s-like and p-like character, so should have a = 0.5 and p = 0.87. In practice, all the defects in Table 4.1 have a slightly smaller s-character and larger p-character and also incomplete localization, compared to the sp dangling bond model. 

Furthermore, the broad TMS signal is similar to the reported silicon-dangling bond centers observed from silane plasma deposition [13,14]. In addition, a well-studied class of paramagnetic silicon defects, the Pb centers [15,16], has precisely the g anisotropy (fig 0.006) required to account for the width of the TMS signal. The overall effect of including all these Pb defects together would be to... 

Similarly, the low frequency overtone at 6950 cm-1 associated with acidic OH vanishes, while the silanol overtone band develops at 7325 cm-1 (9) and the ( v + 6) combination shifts to 4540 cm-1. These observations are consistent with the creation of silicon defects in the structure of dealuminated Y zeolites (10) while the weak overtone band at 7240 cm 1 is probably related to hydroxylated aluminium species extracted from the lattice (11, 12). Thus, the near-IR spectra give evidence for the decrease of the number of Bronsted acid sites as a result of dealumination. 

In doped samples three different ESR responses are observed the usual silicon dangling-bond resonance, a broad resonance attributed to holes trapped in states near the valence-band edge, and a narrow resonance attributed to electrons trapped in states near the conduction-band edge. Two interpretations have been proposed for the presence of these two additional signals—holes or electrons trapped at weak bonds in the band tails and holes or electrons trapped at twofold-coordinated silicon defect sites. 

M. Oota, T. Kanamori, S. Kitamura, H. Fujii, T. Kawasaki, K. Sekine and C. Manabe, Decrease of silicon defects in oxynitride glass, J. Non-cryst. Solids, 209,69-75 (1997). 

Thompson, K., Flaitz, P.L., Ronsheim, P, Larson, D.J., Kelly,TF. (2007) Imaging of arsenic Cottrell atmospheres around silicon defects by three-dimensional atom probe tomography. Science, 317,1370-1374. 

Talanin, V.I. Talanin, I.E. (2004). Mechanism of formation and physical classification of the grown-in microdefects in semiconductor silicon. Defect Diffusion Forum, Vol. 230-232, No. 1, pp. 177-198, ISSN 1012-0386. 

Fig. VIII-2. Scanning tunneling microscopy images illustrating the capabilities of the technique (a) a 10-nm-square scan of a silicon(lll) crystal showing defects and terraces from Ref. 21 (b) the surface of an Ag-Au alloy electrode being electrochemically roughened at 0.2 V and 2 and 42 min after reaching 0.70 V (from Ref. 22) (c) an island of CO molecules on a platinum surface formed by sliding the molecules along the surface with the STM tip (from Ref. 41).

Wang L S, Nicholas J B, Dupuis M, Wu FI and Colson S D 1997 SijO (x = 1-6) models for oxidation of silicon surfaces and defect sites in bulk oxide materials Phys. Rev. Lett. 78 4450... 

The deposition of amoriDhous hydrogenated silicon (a-Si H) from a silane plasma doped witli diborane (B2 Hg) or phosphine (PH ) to produce p-type or n-type silicon is important in tlie semiconductor industry. The plasma process produces films witli a much lower defect density in comparison witli deposition by sputtering or evaporation. 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

J. Vanhellemont, E. Dornberger, J. Esfandyari, G. KLissinger, M. A. Trauwaert, H. Bender, D. Graef, U. Lambert, W. von Ammon. Defects in as-grown silicon and their evolution during heat treatments. Mater Sci Eorum 0 341, 1997. 

T. Sinno, R. A. Brown, W. Van Ammon, E. Dornberger. Point defect dynamics and the oxidation-induced stacking-fault ring in Czochralski-grown silicon crystals. J Electrochem Soc 145 302, 1998. 

The discussion so far has been limited to the structure of pure metals, and to the defects which exist in crysteds comprised of atoms of one element only. In fact, of course, pure metals are comparatively rare and all commercial materials contain impurities and, in many cases also, deliberate alloying additions. In the production of commercially pure metals and of alloys, impurities are inevitably introduced into the metal, e.g. manganese, silicon and phosphorus in mild steel, and iron and silicon in aluminium alloys. However, most commercial materials are not even nominally pure metals but are alloys in which deliberate additions of one or more elements have been made, usually to improve some property of the metal examples are the addition of carbon or nickel and chromium to iron to give, respectively, carbon and stainless steels and the addition of copper to aluminium to give a high-strength age-hardenable alloy. 

---