X-ray diffraction imaging of ZnTe crystals grown by the multi-tube physical vapour transport technique

• High lattice perfection, transparent, 100 mm diameter, bulk crystals of ZnTe.
• Large area, monochromatic beam X-ray topographs.
• Narrow rocking curves.
• Crystal lattice planes parallel to seed show biaxial concavity.
• Crystals on (211B) seeds grow in {331} orientation.

X-ray diffraction imaging (topography) has been used in monochromatic beam mode to demonstrate that 100 mm diameter ZnTe crystals, several millimetres thick, and grown by the multi-tube physical vapour transport technique on (001) and (211B) GaAs substrates, have very high crystal perfection. Images taken in the Bragg geometry from planes containing the growth direction show evidence of cellular dislocation structure and give strong contrast from the whole, several mm2, sample area. Rocking curves taken from small areas show only moderate broadening from that expected from a perfect crystal, indicating dislocation density of typically 3.5×106 cm−2 close to the seed and 3.3×105 cm−2 at the top of the grown crystal. At the top surface, planes parallel to the seed show biaxial concavity, a feature attributed to the ZnTe boule bowing under tensile strain generated at the substrate-crystal interface due to the mismatch in thermal expansion coefficients of GaAs and ZnTe. Crystals grown on (211B) substrates are of {331} orientation, showing no evidence of twin boundaries, suggesting that {331} growth is initiated at, or very close to, nucleation.