Analysis of grain structure evolution via image processing based on optical measurements of mc Si wafers
A fast and thorough characterization of grain structure in multicrystalline silicon (mc-Si) is crucial to improve crystal growth and thus bulk lifetime in solar cells. The presented characterization techniques are based on simple optical measurements on as-cut mc-Si wafers. An insight into the entire brick is gained by connecting 2D-information, computed via advanced pattern recognition techniques, over brick height. We identify robust statistical key parameters. Their development within typical bricks of different cast-Si techniques is compared and it is found that the distinct behavior of different materials in the lower part of the brick subsides towards the brick top where grain size distribution is similar.
Development of grain structures of multi-crystalline silicon from randomly orientated seeds in directional solidification
Abstract Development of grain structures of multi-crystalline silicon from small spherical seeds with random orientations in directional solidification was investigated. The electron backscattered diffraction (EBSD) analyses of the grains at different pulling rates, i.e., 1, 5, and 20 cm/h, were carried out. It was found that {112}/{111} orientations were dominant at the low crucible pulling speed, while {111} at the high pulling speeds. The percentage of {100} grains was found very low near the top of the ingots. The percentage of non-Σ grain boundaries was around 70% at the beginning and decreased with the solidification distance, while Σ3 grain boundaries or twins increased indicating the importance of twin formation during the development of grain structures. The mechanisms for grain competition and selection were further discussed.
An x-ray topographic study on lithium niobate single crystals
Abstract The effect of growth conditions on the crystal perfection in Czochralski-grown LiNbO 3 single crystals was investigated by the X-ray topographic technique. Comparison was made between crystals grown from the stoichiometric and the congruent melts, and between crystals pulled along 〈001〉 and 〈2I0〉 directions. Various kinds of lattice defects, such as dislocations, subgrain boundaries, and gross imperfections at the ferroelectric domain boundaries in an as-grown state, were successfully observed in crystals. Furthermore, as an indication of crystal perfectness, the so-called margin enhancement was observed in the section topographs of a 〈001〉 pulled crystal grown from the fresh congruent melt. The optical quality of crystals was found to be degraded by subgrain boundaries, subgrains with a lattice distortion and gross imperfections at the domain boundaries. These detrimental imperfections could not be completely removed by annealing and poling processes. However, they were found to be considerably controlled by the appropriate selections of the melt composition and pulling axis.