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.

Enhancements in specimen preparation of Cu(In,Ga)(S,Se)2 thin films

When producing slices from Cu(In,Ga)(S,Se)(2) thin films for solar cells by use of a focused ion beam (FIB), agglomerates form on the Cu(In,Ga)(S,Se)(2) surfaces, which deteriorate substantially the imaging and analysis in scanning electron microscopy. Similar problems are also experienced when depth-profiling Cu(In,Ga)(S,Se)(2) thin films by means of glow-discharge or secondary ion mass spectrometry. The present work shows that the agglomerates are composed of (mainly) Cu, and that their formation may be impeded considerably by either cooling of the sample or by use of reactive gases during the ion-beam sputtering. The introduction of XeF(2) during FIB slicing resulted in excellent images, in which the microstructures of most layers in the Cu(In,Ga)(S,Se)(2) thin film stack are visible, including the microstructure of the 20 nm thin MoSe(2) layer. Acquisition of high-quality two-dimensional and also three-dimensional electron backscatter diffraction data was possible. The present work gives a basis for enhanced SEM imaging and analysis not only in the case of Cu(In,Ga)(S,Se)(2) thin films but also when dealing with further material systems exhibiting similar formations of agglomerates.