Main defect reactions behind phosphorus diffusion gettering of iron

Phosphorus diffusion is well known to getter effectively metal impurities during silicon solar cell processing. However, the main mechanisms behind phosphorus diffusion gettering are still unclear. Here, we analyze the impact of oxygen, phosphosilicate glass as well as active and clustered phosphorus on the gettering efficiency of iron. The results indicate that two different mechanisms dominate the gettering process. First, segregation of iron through active phosphorus seems to correlate well with the gettered iron profile. Secondly, immobile oxygen appears to act as an effective gettering sink for iron further enhancing the segregation effect. Based on these findings, we present a unifying gettering model that can be used to predict the measured iron concentrations in the bulk and in the heavily phosphorus doped layers and explains the previous discrepancies reported in the literature.Peer reviewe

A Unified Parameterization of the Formation of Boron Oxygen Defects and their Electrical Activity

AbstractThe magnitude of light-induced degradation of solar cells based on Czochralski grown silicon strongly depends on material properties. We have performed experiments to describe the activation and recombination activity of boron oxygen defects in boron compensated n-type silicon. Compensated n-type material enables flexible assessment of charge carrier influences on the defect that cannot be distinguished on p-type material. The results can be generalized to p-type material and thus provide valuable insights to the defect. Our measurements demonstrate the two-level defect nature of the slow-formed boron oxygen defect component and allow the study of the dopant dependency of the defect concentrations. Our findings strongly support a revision of the existing model of the defect composition.Based on the experimental results and literature data we have created a parameterization of the lifetime limitation in silicon due to BO defects. Established findings from literature for uncompensated p-type silicon are taken into account and ensure general validity. The parameterization is useful to discuss BO defect influences and can serve to predict material properties after LID

Micro-spectroscopy on silicon wafers and solar cells

Micro-Raman (μRS) and micro-photoluminescence spectroscopy (μPLS) are demonstrated as valuable characterization techniques for fundamental research on silicon as well as for technological issues in the photovoltaic production. We measure the quantitative carrier recombination lifetime and the doping density with submicron resolution by μPLS and μRS. μPLS utilizes the carrier diffusion from a point excitation source and μRS the hole density-dependent Fano resonances of the first order Raman peak. This is demonstrated on micro defects in multicrystalline silicon. In comparison with the stress measurement by μRS, these measurements reveal the influence of stress on the recombination activity of metal precipitates. This can be attributed to the strong stress dependence of the carrier mobility (piezoresistance) of silicon. With the aim of evaluating technological process steps, Fano resonances in μRS measurements are analyzed for the determination of the doping density and the carrier lifetime in selective emitters, laser fired doping structures, and back surface fields, while μPLS can show the micron-sized damage induced by the respective processes

Lock-in thermography: basics and use for evaluating electronic devices and materials

This book discusses lock-in thermography (LIT) as a dynamic variant of the widely known IR thermography. It focuses on applications to electronic devices and materials, but also includes chapters addressing non-destructive evaluation. Periodically modulating heat sources allows a much-improved signal-to-noise ratio (up to 1000x) and a far better lateral resolution compared to steady-state thermography. Reviewing various experimental approaches to LIT, particularly the commercial LIT systems available, this 3rd edition introduces new LIT applications, such as illuminated LIT applied to solar cells, non-thermal LIT lifetime mapping and LIT application to spin caloritronics problems. Numerous LIT investigation case studies are also included

Lock-in thermography: basics and use for evaluating electronic devices and materials

This book discusses lock-in thermography (LIT) as a dynamic variant of the widely known IR thermography. It focuses on applications to electronic devices and materials, but also includes chapters addressing non-destructive evaluation. Periodically modulating heat sources allows a much-improved signal-to-noise ratio (up to 1000x) and a far better lateral resolution compared to steady-state thermography. Reviewing various experimental approaches to LIT, particularly the commercial LIT systems available, this 3rd edition introduces new LIT applications, such as illuminated LIT applied to solar cells, non-thermal LIT lifetime mapping and LIT application to spin caloritronics problems. Numerous LIT investigation case studies are also included

Quantum efficiency analysis of high efficiency solar cells with textured surfaces

An analysis of the optical and electrical contributions to the quantum efficiency of the ISE LBSF silicon solar cells with inverted pyramid texturization was performed. A general numerical approach was used based on the new ray tracing program RAYN for modelling reflection, absorption and excess carrier generation combined with the numerical solar cell simulator SoSi-2d. The ray tracing evaluation of a solar cell is based on the comparison with the measured reflectance. It results in detailed spectraly resolved information about which fraction of light is reemitted, absorbed in silicon and absorbed in the rear surface metallization. The separation of volume and rear surface influence on the electrical collection efficiency is investigated with an analytical and the numerical approach

Quantum efficiency analysis of high efficiency solar cells with textured surfaces

An analysis of the optical and electrical contributions to the quantum efficiency of the ISE LBSF silicon solar cells with inverted pyramid texturization was performed. A general numerical approach was used based on the new ray tracing program RAYN for modelling reflection, absorption and excess carrier generation combined with the numerical solar cell simulator SoSi-2d. The ray tracing evaluation of a solar cell is based on the comparison with the measured reflectance. It results in detailed spectraly resolved information about which fraction of light is reemitted, absorbed in silicon and absorbed in the rear surface metallization. The separation of volume and rear surface influence on the electrical collection efficiency is investigated with an analytical and the numerical approach