Norbert Schäfer

Electron-beam-induced current measurements with applied bias provide insight to locally resolved acceptor concentrations at p-n junctions

Electron-beam-induced current (EBIC) measurements have been employed for the investigation of the local electrical properties existing at various types of electrical junctions during the past decades. In the standard configuration, the device under investigation is analyzed under short-circuit conditions. Further insight into the function of the electrical junction can be obtained when applying a bias voltage. The present work gives insight into how EBIC measurements at applied bias can be conducted at the submicrometer level, at the example of CuInSe2 solar cells. From the EBIC profiles acquired across ZnO/CdS/CuInSe2/Mo stacks exhibiting p-n junctions with different net doping densities in the CuInSe2 layers, values for the width of the space-charge region, w, were extracted. For all net doping densities, these values decreased with increasing applied voltage. Assuming a linear relationship between w2 and the applied voltage, the resulting net doping densities agreed well with the ones obtained by means...

Microstrain distributions in polycrystalline thin films measured by X-ray microdiffraction

Microstrain distributions were acquired in functional thin films by high-resolution X-ray microdiffraction measurements, using polycrystalline CuInSe2 thin films as a model system. This technique not only provides spatial resolutions at the submicrometre scale but also allows for analysis of thin films buried within a complete solar-cell stack. The microstrain values within individual CuInSe2 grains were determined to be of the order of 10−4. These values confirmed corresponding microstrain distribution maps obtained on the same CuInSe2 layer by electron backscatter diffraction and Raman microspectroscopy.

Microstrain distribution mapping on CuInSe2 thin films by means of electron backscatter diffraction, X-ray diffraction, and Raman microspectroscopy

The investigation of the microstructure in functional, polycrystalline thin films is an important contribution to the enhanced understanding of structure-property relationships in corresponding devices. Linear and planar defects within individual grains may affect substantially the performance of the device. These defects are closely related to strain distributions. The present work compares electron and X-ray diffraction as well as Raman microspectroscopy, which provide access to microstrain distributions within individual grains. CuInSe2 thin films for solar cells are used as a model system. High-resolution electron backscatter diffraction and X-ray microdiffraction as well as Raman microspectroscopy were applied for this comparison. Consistently, microstrain values were determined of the order of 10(-4) by these three techniques. However, only electron backscatter diffraction, X-ray microdiffraction exhibit sensitivities appropriate for mapping local strain changes at the submicrometer level within individual grains in polycrystalline materials.

Backside failure analysis techniques: What's the gain of silicon getting thinner?

Failure analysis (FA) of electronic devices today is mostly conducted through the device backside. Advanced silicon (Si) backside preparation for this purpose has developed over the past years, with a final Si thickness from around 300μm to 100μm down to around 20μm to 10μm. This paper discusses what to expect if Si can be processed a little thinner, from 20μm down to a few μm. Improvement of optical imaging, spectral extension of photon emission and expanded optical interaction for stimulation techniques are investigated. Further, Si thickness is coming close to the penetration depth of particle beams. The interaction potential for device analysis is discussed, preliminary results are presented.

Comparison of techniques for strain measurements in CuInSe2 absorber layers of thin-film solar cells

1. Helmholtz-Zentrum Berlin fur Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany 2. Freie Universitaet Berlin, Institute of Geological Sciences, Malteserstr. 74-100, 12249 Berlin, Germany 3. Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, U.K. 4. European Synchrotron Radiation Facility, BP 220, Grenoble Cedex, France 5. Federal Institute for Materials Research and Testing, Richard-Willstatter-Str. 11, 12205 Berlin, Germany