Structure defects in silicon-doped (at concentrations 1.7 x 10(19) and 4.5
x 10(19) cm(-3)) GaAs single crystals grown by the method of vertical direc
tional crystallization have been studied. It is shown that the use of the t
riple-crystal X-ray diffractometry in the range of the asymptotic diffuse X
-ray scattering provides the information on microdefects of various types,
sizes, orientations, and symmetries. The specimens cut out from various par
ts of the ingot along the (001) plane showed the presence of interstitial-t
ype dislocation loops of various dimensions and amorphous clusters. The ave
rage dimensions and concentrations of these defects are determined.