THE FORMULATION OF DISLOCATION NETWORKS IN GALLIUM SINGLE CRYSTALS
BROWN UNIV PROVIDENCE RI METALS RESEARCH LAB
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The development of dislocation networks in gallium crystals, initially free of detectable dislocations, was studied at room temperature by an x-ray diffraction topographic technique. The condition required for the development of these networks is the existence of spatial periodic fluctuations in impurity content. The networks develop, in the absence of an external stress, from individual loops which are first detected 3 to 10 days after the crystal has been grown. These loops grow for days at a uniform rate of 10 to the minus 8th power cmsec and reach a size of a few hundred microns. No specific nucleation mechanism for these loops has been identified. If it is assumed that the loops expand by climb by the addition of vacancies, their rate of growth and observed densities are consistent with a formation energy for vacancies U sub f in the range 0.2 to 0.3 ev and a migration energy for vacancies U sub m in the range 0.4 to 0.7 ev. No values of U sub f, U sub m or U sub f U sub m determined from other experiments have been reported and a comparison is not possible at the present time. The change of initially straight dislocation lines into jagged lines has been observed and is interpreted as the climb of screw dislocations into irregular helical dislocations. A marked anisotropy in the growth of the loops and helices was observed and is attributed to an anisotropic coefficient of self-diffusion.