Micro-spectroscopy on silicon wafers and solar cells

Fraunhofer Institute for Solar Energy Systems (ISE), Heidenhofstr, 2, 79110 Freiburg, Germany. .
Nanoscale Research Letters (Impact Factor: 2.78). 03/2011; 6(1):197. DOI: 10.1186/1556-276X-6-197
Source: PubMed


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.

Download full-text


Available from: Martin C. Schubert
  • Source
    • "Recently Micro-Raman-Spectroscopy and Micro-Photoluminescence Spectroscopy (μRS, μPL) gained significant importance in the characterization of microscopic structures in silicon for solar cells. The investigated objects reach from grain boundaries [1] and precipitates [2] to local highly doped regions, epitaxial layers and laser induced processes [3]. The parameters under consideration are doping density, carrier lifetime, stress and crystallinity. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Significant improvements in the experimental setup of Micro-Raman (μRS) and Micro-Photoluminescence-Spectroscopy (μPL) for solar cell characterization are reported. The lateral resolution of doping density mapping with μRS is improved to below 200 nm. A highly resolved measurement on an aluminum BSF demonstrates the increase in resolution. Furthermore, the characterization of thin silicon layers within the same experimental setup is presented. An excitation source with low penetration depth is used to screen out background signal from the substrate. Finally, a surface topography mapping technique is implemented to extend μRS and μPL to uneven surfaces. With this extension micro cracks in conventionally textured silicon solar cells could be successfully characterized.
    Full-text · Article · Dec 2012 · Energy Procedia
  • [Show abstract] [Hide abstract]
    ABSTRACT: Manufacturing defects are more likely to be introduced into cable during the jointing processes, due to the manual nature of this procedure. These defects can reduce the working lifetime of the cable. It is possible to detect these defects using X-ray techniques and photographic film, however there are problems associated with this procedure. To remove these problems the photographic plate can be replaced by a CCD array coupled to a scintillating screen. To ensure that there is no loss in image quality a comparative test has been conducted to compare the images generated using both film and CCD technologies. This test involved generating images of three test pieces using both film and the CCD camera. The film images were then digitised using a scanner so that they could be digital processed. Two algorithms were then used to process these images, a statistical based algorithm and a Newtonian based algorithm. The results of processing these images are discussed and indicate the viability of an automated digital X-ray cable inspection system.
    No preview · Conference Paper · Aug 2004
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We introduce a comprehensive characterization approach of microscopic technological structures in advanced silicon cell concepts. Micro-photoluminescence spectroscopy and micro-Raman spectroscopy with their submicron resolution potential are applied, which allow a direct extraction of the most important parameters. These parameters are the micron resolved carrier lifetime, the doping density and the stress induced by the process. This paper covers exemplary measurements, which demonstrate the potential of this characterization approach for process optimization, details on the measurement techniques and on the sample preparation. The structures under test are laser doped back surface fields, nickel-plated contacts, back contact structures and epitaxial layers. The presented characterization techniques are able to reveal microscopic flaws in the technological structures and thus, allow for a direct and targetoriented optimization of the investigated processes.
    Full-text · Conference Paper · Dec 2011
Show more