Characterization of defect structures in magnetic liquid encapsulated Kyropoulos grown InP single crystals

Abstract

Synchrotron White Beam X-ray Topography (SWBXT) has been used as a nondestructive diagnostic technique for the characterization of defect structures in large wafers cut from S and Fe-doped InP single-crystal boules. Wafers cut both longitudinally and laterally with respect to the growth axis were studied in order to reveal the overall defect distribution in the boules. Studies carried out on longitudinally cut S-doped crystals enabled information to be obtained on interface shape, from the observation of growth striations, as well as defect distribution. The conditions for optimal visibility of the growth striations were determined and it was found that the morphology of the growth interface was a sensitive function of local growth conditions. The formation of extensive slip bands from peripheral regions was also observed. This indicates that large thermal stresses were generated during crystal growth leading to such significant plastic deformation processes. Studies carried out on a series of laterally sliced, Fe-doped wafers cut from the same boule revealed dislocations in well-defined fourfold symmetric distributions. A finite element thermal-elastic stress analysis was performed for an intermediate growth stage to investigate the nature of the stress which causes this fourfold distribution. The calculated excess shear stress from this analysis agrees qualitatively with the observed dislocation distribution and slip system activity. The influence of an applied magnetic field on precipitate distributions in InP boules was preliminarily studied by examining a longitudinal cut, heavily Fe-doped InP wafer, which was grown in the presence of an intermittent applied field. Topographs recorded from this wafer revealed that no formation of large precipitates was discernible in either the initial or intermediate growth stages when the magnetic field was applied. On the other hand, the formation of large precipitates was observed in regions near the final stage of crystal growth when the magnetic field was turned off. Further such investigations are underway.