Analysis of types of residual dislocations in the VGF grwoh of GaAs with ekxtremely low dislocation density (EPD1000 cm~-2)

摘要

GaAs single crystals (silicon-doped, 2 inch) with extremely low dislocation densities (etch pit density (EPD) 5-100 cm~-2 were grown by the vertical gradient freeze method. In these crystals we characterised different types of dislocations by the aid of white beam X-ray diffraction topography and infrared transmission microscopy. It was found for decreasing disloction densioties (EPD<200 cm~-2), that dislocations having a lien vector l, Which is parallel to the [0 0 1] growth direction of the crystals, become more and more domainant. These residual disloctions are induced by the seeding process (so far we were using LEC-grwn seed crystals). These residual dislocations cannot are induced by the seeding process (so far we were using LEC-grown seed crystals). These residual disloctions cannot be avoided by minimising the thermal stress during the crystal growth process.