Recombination Activity of Metal-related and Boron-oxygen Defects in Crystalline Silicon

Abstract

This thesis aims to improve the understanding of the recombination activity of some metal-related defects and the boron-oxygen (BO) defect in crystalline silicon. First, the recombination parameters of the aluminium-oxygen (Al-O) complex are reassessed by applying lifetime spectroscopy on several n- and p-type Al-contaminated samples. The uncertainty ranges of the recombination parameters have been tightened significantly by simultaneously fitting the lifetimes measured on several differently doped samples. The same method is also applied on several n- and p-type Cr-contaminated samples, to determine the defect parameters of interstitial Cr and CrB pairs. Direct experimental comparisons have shown that both the Al-O defect and Cr have greater negative impacts on carrier lifetimes in p-type silicon than in n-type silicon at low to intermediate injection levels. One approach to reduce the recombination activity of the defects is via hydrogen passivation. The charge state of monatomic hydrogen plays a key role in the passivation process. In this thesis, we describe and apply a rigorous approach to calculating the charge states of monatomic hydrogen, as well as Fe, Cr and the BO defect, as a function of both temperature and injection level. Based on these results, the impact of temperature and injection on the hydrogenation of the key defects, and other pairing reactions, are discussed. In the experimental investigation of the potential hydrogenation of Fe, significant reductions of interstitial Fe concentration are observed in samples passivated with hydrogen-rich silicon nitride films, but not in samples with hydrogen-lean silicon oxide films. We have measured and modelled the Fe reduction kinetics over a wide temperature range, assuming that the reduction is caused by hydrogenation, based on the charge state model. However, a subsequent study has shown conclusively that Fe is gettered by the nitride films. Based on this new finding, the kinetics data are re-analysed in this thesis. For Cu and Ni precipitates, both photoluminescence (PL) images and micro-PL maps are taken on several n-type and p-type wafers in which Cu or Ni has precipitated during the ingot cooling. The high-injection micro-PL measurements significantly reduce the carrier diffusion, allowing more highly resolved inspection of the particles. Markedly different precipitation patterns were observed in n- and p-type samples. The effects of the intrinsic point defect on the precipitation behaviour of the metals, and the dopant effects on the intrinsic point defect concentrations, are discussed based on the results. High-injection micro-PL measurements are also valuable to study the activation kinetics of the BO defect because (a) the activation is significantly accelerated, allowing it to be studied in shorter timeframes, and (b) the injection level can be kept constant over time and in differently doped samples, as the high-injection lifetime is dominated by Auger recombination. This allows the activation time constant and defect concentration in differently doped samples to be compared more directly. Therefore the micro-PL system is used to measure the activation kinetics of the BO defect in compensated n- and p-type silicon. The results obtained under high-injection conditions help to clarify some unresolved issues related to the defect. Show more