A study on dislocation lines in an In-doped LEC GaAs crystal by IR light scattering and transmission microscopy

Abstract

Defects, especially dislocations in an In-doped GaAs crystal grown along [001] by liquid encapsulated Czochralski (LEC) method, were microscopically visualized by infrared light scattering tomography to study growth history and mechanism of the crystal. Here, three types of dislocations were found: (i) Grown-in dislocations, in which helical and bent dislocations were included. (ii) Dislocations introduced within liquid-solid interfaces. Some ends of the dislocations penetrated into the just-grown ingot and slipped on the (100) planes due to thermal stresses, because the ingot was still growing with a large temperature gradient from its molten phase. The opposite end terminals remained within the interfaces at their initial stages but some of them reacted between themselves to diminish their density or to make a linkage with the terminals. The terminals and some other dislocation ends acted as origins of the grown-in dislocations. (iii) A lot of dislocations were introduced into the ingot from its outer-side surface by thermal stresses during its cooling stage after the growth.