Electrical Properties of Silicon with Bistable Impurity Complexes
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1210-Q08-18
ELECTRICAL PROPERTIES OF SILICON WITH BISTABLE IMPURITY COMPLEXES S. Zh. Karazhanov, T. U. Nærland, J. Mayandi, R. Søndenå, and A. Holt Department of Solar Energy, Institute for Energy Technology, 2027 Kjeller, Norway ABSTRACT Many impurity complexes in silicon such as boron-oxygen and iron-aluminium complexes are found to be bistable. Such defect complexes can be in two different configurations separated by a potential barrier. Commonly bistable recombinative complexes in silicon are studied through carrier lifetime experiments and are analysed by use of Shockley-Read-Hall (SRH) recombination theory. SRH recombination theory is valid for stable defects with one configuration and one energy level in the band gap. However, the theory might fail when applied to the recombination centers formed by bistable defects. This work presents a theoretical study of electrical properties of silicon with bistable impurity complexes. The analysis has been performed for statistics of free electrons and holes, their recombination rate and lifetime. The results have been compared with those obtained from the SRH recombination theory. INTRODUCTION Carrier lifetime is one of the key parameters affecting the performance of many semiconductor devices, such as solar cells [1]. Today a range of different lifetime spectroscopy methods are available [2-4], including quasi-steady state photo-conductance measurements and microwave photoconductance decay measurements which are widely used for the characterization of solar cell materials. For theoretical analysis the SRH| recombination theory [5,6] is commonly used. This theory can be applied for deep-level defects which have one configuration and possess one energy level in the band gap [7,8]. Some defects in Si are reported to be bistable. Examples are complexes of interstitial and substitutional carbon atoms (Ci-Cs) [9-11], interstitial Fe and substitutional Al (FeiAls) [12,13], a vacancy and two O atoms (VSi-O2i) [14,15], interstitial carbon and a substitutional donor (D) where the donor is a group-V element (Ci-Ds) [16,17], Cu-S and Cu-Se pairs as well as the Si-O complex [18]. Systematic analysis of bistable and metastable defects has been performed in Refs. [12,18]. Another candidate for the bistable defect is the widely studied boron-oxygen (B-O) complex, which causing degradation of efficiency of the Czochralski-grown silicon (Cz-Si) based solar cells by up to 10% under illumination at room temperature [19]. A bistable defect is suggested to be the reason for the degradation [20], which consists of one substitutional boron atom and one interstitial oxygen dimer (O2i) [20]. The origin of the defect has been discussed by density functional calculations and the formation mechanism and properties of the complex are suggested.21 According to findings of Ref. [21] B traps O2i to form a bistable defect with a donor level in the upper half of the band gap with an activation energy for dissociation of ~1.2 eV. Recently, it is reported that the B-O complex can be deactivated by simul
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