Theoretical Investigation of Nitrogen-Doping Effect on Native Defect Aggregation Processes in Silicon
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Theoretical Investigation of Nitrogen-Doping Effect on Native Defect Aggregation Processes in Silicon H. Kageshima,1 A. Taguchi,1 and K. Wada2 1 NTT Basic Research Labs., NTT Corporation, Atsugi, Kanagawa 243-0198 Japan. 2 Massachusetts Institute of Technology, Cambridge, Massachusetts, USA ABSTRACT We theoretically investigated interactions between nitrogen (N) atoms and Si native defects, vacancy (V) and interstitial (I), by using first-principles calculations in order to shed light on the nitrogen-doping effect on the defect aggregation processes. Stabilities of various N-I and N-V complexes are examined by calculating the total energy. We found that N atoms form stable complexes with both of V and I. The formation of such stable complexes reduces the effective concentrations of the native defects, resulting in the suppression of aggregation processes of V and I.
INTRODUCTION Nitrogen (N) doping in Si has received considerable attention because it has been clear that rather small amount of N (-1015 cm-3) significantly improves crystal quality both of Czochralski Si (CZ-Si) [1] and floating-zone Si (FZ-Si) [2]. In CZ-Si, it is experimentally observed that void, which is large aggregates of vacancy (V), becomes smaller in size and larger in density due to the N-doping. The reduction of the void formation temperature was also observed. These observations clearly indicate that the N-doping suppresses the V aggregation. Abe et al. reported that the N-doping also reduces A defect in FZ-Si , which is the aggregate of Si interstitials (I) [2]. The doped N in Si affects other impurities and defects. Enhancement of oxygen precipitation was observed in CZ-Si [3]. This property can be used for controlling the quality of Si crystal. It is also known that the N-doping increases the mechanical strength by suppressing the formation of swirl defects and locks dislocations [4]. In the electrical properties, deep levels due to the N doping were observed and discussed [1,5]. These various experimental results clearly show the N doping effects, but the microscopic mechanism has not been clarified. In this paper, we discuss the N-doping effect on the aggregation processes of V and I, which are the most recent attractive and important topic. Recently, two groups reported first-principles calculation results of N-V complexes [6,7]. Both groups concluded that N forms stable complexes with V, and such stable complexes bring the suppression of the V aggregation. We will explain the theoretical results and discuss the mechanism of the N effect on the V aggregation processes. As to the suppression of the I-related aggregates, Ammon et al. suggested that the suppression of the I aggregates is resulted from the pair recombination of V and I with a help of stable N-V complexes [8]. However, there are no first-principles investigations of N-I complexes, and the stability of N-I complexes are not clear F3.3.1
yet. We examined the stability of N-I complexes and found that N also forms stable complexes with I. We will discuss the N roles in the
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