Impact of isovalent defect engineering strategies on carbon-related clusters in silicon
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Impact of isovalent defect engineering strategies on carbon-related clusters in silicon C. A. Londos • E. N. Sgourou • A. Chroneos
Received: 25 September 2012 / Accepted: 10 November 2012 / Published online: 23 November 2012 Ó Springer Science+Business Media New York 2012
Abstract In electron-irradiated silicon (Si) the formation of oxygen-vacancy pairs (VO or A-centers) is deleterious and for this reason isovalent defect engineering strategies have been proposed to suppress their concentration. Carbon-related clusters such as CiOi and CiCs are also important as they are electrically active and their properties need to be determined. The present study has two aims. The first aim is to review the impact of isovalent doping [germanium (Ge), tin (Sn) and lead (Pb)] on the thermal stability of the CiOi and CiCs pairs in Si by means of infrared (IR) spectroscopy. The second aim is to analyze these results and show that the presence of isovalent dopants in Si reduces the temperature of annealing (Tann) of the CiOi pairs and increases the temperature of annealing of the CiCs pairs. The results are discussed in view of recent experimental and theoretical studies. It is suggested that the change in the thermal stability of the C-related defects is due to the local strains induced in the lattice by the oversized isovalent dopants. It is surmised that these strains have an opposite impact on the Tann of the CiOi and CiCs pairs as a result of their different structures.
C. A. Londos E. N. Sgourou Solid State Physics Section, University of Athens, Panepistimiopolis Zografos, 157 84 Athens, Greece A. Chroneos Materials Engineering, The Open University, Milton Keynes MK7 6AA, UK A. Chroneos (&) Department of Materials, Imperial College, London SW7 2AZ, UK e-mail: [email protected]
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1 Introduction The properties of semiconductors are affected and can be tuned by the control of defects and doping [1–4]. In recent studies defect engineering strategies involving oversized isovalent dopants (Ge, Sn, Pb) were employed to suppress the formation of A-centers in Si [5]. In essence the oversized isovalent dopants trap vacancies limiting their availability for VO formation [5]. There are strong indications that Ge doping can enhance the radiation hardness of Si [6–12]. The potential of radiation hardness has also been demonstrated for Sn [13, 14] and Pb [15, 16] dopants in Si. The introduction of these oversized isovalent impurities in the Si lattice gives rise to local strain fields [17] affecting the properties of the intrinsic point defects (i.e. vacancies and self-interstitials). Consequently, the formation of radiation defects is expected to be affected and this is verified experimentally, both by electrical and optical techniques [6–16]. The efficacy of the defect engineering strategy will depend upon the impact it will have on the defect processes of all the impurities in the material. In Czochralski-grown Si (Cz-Si) carbon is unintentionally added in the lattice during crystal growth. C is isovalent to Si and
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