Grown-in defects limiting the bulk lifetime of p-type float-zone silicon wafers

Abstract

We investigate a recombination active grown-in defect limiting the bulk lifetime (s bulk) of high quality float-zone (FZ) p-type silicon wafers. After annealing the samples at temperatures between 80 C and 400 C, s bulk was found to increase from $500 ls to $1.5 ms. By isochronal annealing the p-type samples between 80 C and 400 C for 30 min, the annihilation energy (E ann) of the defect was determined to be 0.3 < E ann < 0.7 eV. When the annihilated samples were phosphorus gettered at 880 C or subject to 0.2 sun illumination for 24 h, s bulk was found to degrade. However, when the samples were subsequently annealed at temperatures between 250 and 400 C, the defect could be re-annihilated. The experimental results suggest that the defect limiting the lifetime in the p-type FZ silicon is not related to fast diffusing metallic impurities but rather to a lattice-impurity or an impurity-impurity metastable defect. V

Light-induced activation and deactivation of bulk defects in boron-doped float-zone silicon

“…Re-passivation treatments of samples in initial, degraded and recovered state demonstrated the changes in s eff to arise from recombination in the wafer bulk, indicating activation and deactivation of recombination active defects. The capture coefficient ratio factor Q of 35 6 10 we have determined on our samples agrees well with the results of Grant et al 2 and is similar to the value reported by Sperber et al 3 (their reported capture cross section ratios would resemble Q-factors of 30 and 24, respectively). The measurements render BO defects unlikely candidates for the defect, as the injection dependence of s def does not match the known BO defect species.…”

“…2,3 This effect was addressed as light-induced degradation (LID). It indicates formation or activation of defects in the FZ silicon wafer bulk under conditions that can become relevant for the application of solar cells depending on their location.…”

On the c-Si/SiO2 interface recombination parameters from photo-conductance decay measurements

“…74 Recent reports have shown that high purity float zone silicon can develop point defects thus lowering its bulk lifetime. 75,76 When calculating SRV, a lower bulk lifetime would lead to lower values of SRV. To account for this, the lower limit of the error bars in S ef f was calculated using a bulk lifetime affected by an extrinsic Shockley-Read-Hall defect.…”

“…Resistance was then measured using a Keithley SMU yielding a resistivity of 0.92 X cm, thus a phosphorous doping concentration of 5.4 Â 10 15 cm À3 , according to the calculator in Ref. 75.…”

Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications

“…One set of wafers was then subjected to ALD Al 2 O 3 passivation (10 nm on each side) as a reference, and wafers from the other set were quartered for etch-back experiments using SA as the passivation scheme. Prior to the SA treatment (during the etch-back experiment), the silicon samples were subjected to a 200°C anneal for 30 min in order to inhibit bulk degradation [37]. Following the anneal, the samples were etched in 25% TMAH for 20-30 min at ∼ 80°C followed by SC 2 cleaning, 2% HF dip, and SA treatment.…”