Lifetime-degrading boron-oxygen centres in p-type and n-type compensated silicon

Abstract

Degradation of minority carrier lifetime under illumination occurs in boron-containing Czochralski silicon of both p- and n-type. In n-Si, the recombination centre responsible for degradation is found to be identical to the fast-stage centre (FRC) known for p-Si, where it is produced at a rate proportional to the squared hole concentration, p2. Holes in n-Si are the excess minority carriers—of a relatively low concentration; hence, the time scale of FRC generation is increased by several orders of magnitude when compared to p-Si. The degradation kinetics, which is non-linear, due to dependence of p on the current concentration of FRC, is well reproduced by simulations. The injection level dependence of the lifetime shows that FRC exists in 3 charge states (− 1, 0, + 1) possessing 2 energy levels. Comparison of n-Si samples of various electron concentrations shows that FRC emerges by the reconstruction of a latent BsO2 complex of a substitutional boron and an oxygen dimer (while the major recombination centre in p-Si denoted SRC was previously found to emerge by reconstruction of BiO2 defect involving an interstitial boron atom). A model of the BsO2 reconfiguration into FRC through an intermediate state accounts for the rate constant dependence on p, which is reduced to a p2 proportionality, under certain conditions.

Studying Light-Induced Degradation by Lifetime Decay Analysis: Excellent Fit to Solution of Simple Second-Order Rate Equation

“…In 2009, however, Macdonald et al [6] discovered that in p-type material co-doped with boron and phosphorus, where the hole concentration p 0 is smaller than [B], N t * sat was found to be proportional to p 0 and not to [B]. This finding invalidated the model of Schmidt et al, and a new model was later proposed by Voronkov and Falster [7], [8]. In a recent work by Forster et al [9], however, where silicon co-doped with boron and gallium was investigated, it was found that the defect concentration was proportional to [B] instead of p 0 .…”

“…3). Other groups have reported that degradation typically occurs during the first hours of illumination [8], [15], [16]. In this work we experience that only samples with a hole concentration p 0 above 9 × 10 15 cm -3 saturate within 24 hours.…”

“…5 and the discussion in chapter IV-B k is strongly correlated with p 0 . Relating this to the slow defect reaction model by Voronkov et al [7], [8], summarized in the introduction, these results point towards step 2 (7) as the rate determining step. This, however, contradicts the suggestion by Voronkov et al, which proposes the last step as rate limiting.…”

“…Note that the first explanation model where p 0 is embedded in a pseudo rate constant does not contradict Voronkovs model. Several groups have already reported the involvement of two holes/two boron atoms in the reaction kinetics [5][6][7][8][9].…”

“…In the model by Voronkov and Falster [7], [8], a latent recombination center is already incorporated in the crystal before carrier injection. According to this model, the centers responsible for the rapid and slow lifetime decays are B s O 2i and B i O 2i respectively.…”