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Micro-spectroscopy on silicon wafers and solar cells.

Gundel P, Schubert MC, Heinz FD, Woehl R, Benick J, Giesecke JA, Suwito D, Warta W - Nanoscale Res Lett (2011)

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Fraunhofer Institute for Solar Energy Systems (ISE), Heidenhofstr, 2, 79110 Freiburg, Germany. paul.gundel@ise.fraunhofer.de.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Doping density and carrier lifetime in PassDop sample. (a) Qualitative doping density, which is significantly increased in the laser-induced doping region (at the upper surface between the green lines) and (b) damage (map of the μPLS intensity) at the edges of the laser affected region which decreases the lifetime (white arrows).
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Figure 7: Doping density and carrier lifetime in PassDop sample. (a) Qualitative doping density, which is significantly increased in the laser-induced doping region (at the upper surface between the green lines) and (b) damage (map of the μPLS intensity) at the edges of the laser affected region which decreases the lifetime (white arrows).

Mentions: In this section, we qualitatively analyze the cross section of a laser-induced BSF. Local highly doped regions are prepared by point wise laser irradiation of a silicon surface which was previously coated by a phosphorous containing passivation layer [4]. By laser irradiation, the dopant source and the underlying silicon is molten and a phosphorous diffusion in the liquid volume takes place resulting in a local, highly n-doped region. This high doping density underneath the subsequently evaporated metal contacts effectively suppresses recombination at the contact points and furthermore results in a low contact resistance. The high doping is visible by a shift of the PL peak to higher wavelengths (Figure 7a). The PL shift is caused by the decrease of the bandgap at higher doping densities. In Figure 7b, the micron-sized damage, which is caused by the laser process, can be seen at the edges of the laser processed area (white arrows) by a qualitative μPLS image map. This damage at the edges could be caused by the strong thermal gradient in this region during the laser firing. Another reason for the visibility of the damage is that there is no back surface field at the edges, which could passivate the damaged region. This shows the special care which has to be taken for the process laser profile in order to minimize the thermal stress in the edge regions.


Micro-spectroscopy on silicon wafers and solar cells.

Gundel P, Schubert MC, Heinz FD, Woehl R, Benick J, Giesecke JA, Suwito D, Warta W - Nanoscale Res Lett (2011)

Doping density and carrier lifetime in PassDop sample. (a) Qualitative doping density, which is significantly increased in the laser-induced doping region (at the upper surface between the green lines) and (b) damage (map of the μPLS intensity) at the edges of the laser affected region which decreases the lifetime (white arrows).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211253&req=5

Figure 7: Doping density and carrier lifetime in PassDop sample. (a) Qualitative doping density, which is significantly increased in the laser-induced doping region (at the upper surface between the green lines) and (b) damage (map of the μPLS intensity) at the edges of the laser affected region which decreases the lifetime (white arrows).
Mentions: In this section, we qualitatively analyze the cross section of a laser-induced BSF. Local highly doped regions are prepared by point wise laser irradiation of a silicon surface which was previously coated by a phosphorous containing passivation layer [4]. By laser irradiation, the dopant source and the underlying silicon is molten and a phosphorous diffusion in the liquid volume takes place resulting in a local, highly n-doped region. This high doping density underneath the subsequently evaporated metal contacts effectively suppresses recombination at the contact points and furthermore results in a low contact resistance. The high doping is visible by a shift of the PL peak to higher wavelengths (Figure 7a). The PL shift is caused by the decrease of the bandgap at higher doping densities. In Figure 7b, the micron-sized damage, which is caused by the laser process, can be seen at the edges of the laser processed area (white arrows) by a qualitative μPLS image map. This damage at the edges could be caused by the strong thermal gradient in this region during the laser firing. Another reason for the visibility of the damage is that there is no back surface field at the edges, which could passivate the damaged region. This shows the special care which has to be taken for the process laser profile in order to minimize the thermal stress in the edge regions.

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Fraunhofer Institute for Solar Energy Systems (ISE), Heidenhofstr, 2, 79110 Freiburg, Germany. paul.gundel@ise.fraunhofer.de.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus