CHARACTERIZATION OF STRUCTURAL DEFECTS IN MLEK GROWN INP SINGLE-CRYSTALS USING SYNCHROTRON WHITE-BEAM X-RAY TOPOGRAPHY

Structural defects in MLEK grown InP single crystals have been studied using synchrotron white beam X-ray topography. Results here are prese nted for both a S-doped boule which was wafered longitudinally (i.e., parallel to the growth axis) and an Fe-doped boule which was wafered l aterally (i.e., perpendicular to the growth axis). For longitudinal wa fers from the S-doped boule, slip bands were observed to have nucleate d from high-stress concentration located at the peripheral regions of the boule and to have propagated into the interior of the samples. In the same crystals, the growth interface morphology at different stages of crystal growth was determined. The interface is revealed as contou rs of equal lattice parameter, visible via strain contrast, as the con centration of the dopant changed periodically during growth. The inter face shape was observed to be slightly convex to the melt, once the gr owth conditions were stabilized. For the laterally sliced wafers from the Fe-doped boule, systematic studies revealed that the density of di slocations changed during growth. A high density of uniformly distribu ted dislocations were observed in wafers taken from the early and late r stages of growth. On the other hand, dislocations in well-defined fo ur-fold symmetric distributions were observed in wafers sliced from th e intermediate growth stages. The origins of this four-fold distributi on were investigated using a thermal stress model which consisted of i mposing a compressive radial stress, uniformly distributed around the boule circumference. The calculated stress distributions also showed f our-fold symmetry in agreement with the observed dislocation distribut ions.