Jan 24, 2018

Compositional, strain contour and property mapping of CdZnTe boules and wafers

The authors have developed detailed non-destructive mapping and spatial imaging techniques for comparing boule and wafer properties with analytical predictions from high-fidelity process models for seeded vertical Bridgman-Stockbarger growth of CdZnTe crystals. They have emphasized the prediction of the magnitude and distribution of residual stress and strain, as well as longitudinal and radial segregation within the boules and across wafers cut from the boules. Boule and wafer compositional distributions were mapped using photoreflectance, precision lattice parameter measurements and FTIR spectroscopy. Defect and strain distributions within the boules and wafers were imaged using synchrotron topography, synchrotron strain contour mapping, and double-crystal rocking-curve mapping. Thermomechanical and thermosolutal models specifically addressing the seeded vertical Bridgman-Stockbarger growth of CdZnTe crystals were developed and empiricized. These models addressed solute redistribution and stress generation as a result of the interface shape, aspect ratio and growth parameters during the seeding, initial transient (including the shoulder), steady-state and terminal transient regions of the boule. Finally, the stress and strain distributions on specific wafers 'cut' from the processed (modelled) boules were predicted and X-ray synchrotron strain contour, double-crystal rocking-curve, FTIR, and photoreflectance maps were generated on the real wafers for comparison. Implications of these results with respect to substrate quality, screening, performance and producibility, will be discussed.


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