ELECTRICAL AND THERMAL PROPERTIES OF THE METASTABLE DEFECT IN BORON-DOPED CZOCHRALSKI SILICON (CZ-SI)

摘要

Lifetime degradation observed in boron-doped Czochralski silicon (Cz-Si) has its origin in a metastable defect that is activated under illumination or forward bias and deactivated under an anneal at around 200°C. To give insight into the physical mechanism underlying this defect transformation, the first part of this study is focused on the kinetics of defect formation and annihilation. For the process of defect formation, the quantitative analysis of this work clearly shows that it cannot be directly described by the mechanism of recombination-enhanced defect reaction (REDR) as it has been proposed in recent studies. While REDR predicts for the defect generation rate U_(gen) a linear dependence on the doping concentration N_A and the injection level Δn, a quadratic doping and a vanishing injection dependence is found by an improved time-resolved degradation experiment measured with quasi-steady-state photoconductance technique. The experiment reveals that U_(gen) reaches almost its maximum value if Δn only lies above some threshold value, which is already reached for an illumination with 1 mW/cm~2 on a 0.86 Ωcm Cz-sample. For the process of defect annihilation, an isothermal annealing experiment reveals that it is thermally activated with an energy barrier E_(barr) = 1.32 +- 0.05 eV, determined for the first time. The last part of the study is dedicated to the electronic structure of the defect. From temperature-dependent lifetime spectroscopy (TDLS) an upper limit of 0.41 eV is found for the energy level of the Cz-defect in its active state. If the TDLS-result of this work is combined with the energy range determined by Schmidt et al. from injection dependent lifetime spectroscopy, the energy level of the defect in its active state can be further localized in the lower band half at E_V + 0.35 ... 0.41 eV.