Reassessment of the recombination parameters of chromium in n- and p-type crystalline silicon and chromium-boron pairs in p-type crystalline silicon

Abstract

Injection-dependent lifetime spectroscopy of both n-and p-type, Cr-doped silicon wafers with different doping levels is used to determine the defect parameters of Cr i and CrB pairs, by simultaneously fitting the measured lifetimes with the Shockley-Read-Hall model. A combined analysis of the two defects with the lifetime data measured on both n-and p-type samples enables a significant tightening of the uncertainty ranges of the parameters. The capture cross section ratios k ¼ r n /r p of Cr i and CrB are determined as 3.2 (À0.6, þ0) and 5.8 (À3.4, þ0.6), respectively. Courtesy of a direct experimental comparison of the recombination activity of chromium in n-and p-type silicon, and as also suggested by modelling results, we conclude that chromium has a greater negative impact on carrier lifetimes in p-type silicon than n-type silicon with similar doping levels. V

Prediction of local temperature‐dependent performance of silicon solar cells

“…A trap level E t of 0.265 eV (Figure B), which represents chromium‐boron pairs at these temperatures, results in a very different behavior: With decreasing Δn , a strong temperature dependence of τ SRH is observed: τ SRH decreases with declining Δn for low to medium temperatures, whereas τ SRH strongly increases for decreasing Δn at 70°C. This is only an example for a possible impurity inducing SRH recombination with an energy level in the band gap of silicon.…”

Interaction of Chromium Atoms with Dislocations and as‐Grown Vacancy Complexes and its Impact on the Electronic Properties of FZ‐Si

“…Chromium is one of the dangerous impurities that can be often found in solar grade silicon. It is known that interstitial chromium atoms Cr i in n‐Si and Cr i B s pairs in p‐Si can significantly reduce the lifetime of minority carriers and, therefore to reduce significantly the efficiency of solar cells . Using DLTS it was found that interstitial Cr i atom has one donor level at E Cri = E C – 0.22 eV in the upper half of the band gap while the Cr i B s pairs have a donor level of E CrB = E V + 0.28 eV in the lower half of the band gap .…”

Transition Metals in a Cast‐Monocrystalline Silicon Ingot Studied by Silicon Nitride Gettering

“…After passivation, the dissolved interstitial Fe and Cr concentrations ([Fe i ] and [Cr i ]) in the wafers in the lifetime group were determined with the following procedure: a) The wafers were kept at 53 °C in the dark on a hotplate for >3 days to fully associate both FeB and CrB pairs, before the lifetime τ assoc was measured using a Sinton Instruments WCT‐120 quasi‐steady‐state photoconductance lifetime tester. b) A flashlight was used to illuminate the samples to fully dissociate the FeB pairs, and the lifetime was measured.…”

“…b) A flashlight was used to illuminate the samples to fully dissociate the FeB pairs, and the lifetime was measured. The illumination does not dissociate CrB pairs . This lifetime measured after illumination, where FeB pairs were fully dissociated but CrB pairs were fully associated, was denoted as τ ls .…”

“…c) The wafers were then annealed at 260 °C in the dark for 8 min and subsequently quenched in cold water. This process can effectively dissociate >95% CrB pairs in all the wafers . After quenching, the samples were illuminated again with the flashlight for a short time to make sure that the FeB pairs remain dissociated, before the lifetime τ quench was measured.…”