The prospect of technical applications has induced a lot of interest in the atomic structure of the GaAs on Si(100) interface and the defects in its vicinity which are often studied by high resolution transmission electron microscopy. The interface structure is determined by the 4.1% lattice constant mismatch between GaAs and Si, the large difference between the thermal expansion coefficients and the polar/nonpolar nature of the GaAs on Si interface. The lattice constant mismatch is compensated by misfit dislocations which are characterized by a/2<110> Burgers vectors b which are oriented parallel or inclined on {111} planes with respect to the interface. Stacking faults are also frequently observed. They are terminated by partial dislocations with b = a/6<112> on {111} planes. In this report, the atomic structure of stair rod misfit dislocations is analysed which are located at the intersection line of two stacking faults at the interface.A very thin, discontinous film of GaAs has been grown by MBE on a Si(100) substrate. Fig.1.a. shows an interface section of a 27 nm wide GaAs island along [110] containing a stair rod dislocation. The image has been taken with a JEOL 2000EX with a spherical aberration constant Cs = 1 mm, a spread of focus Δz = 10 nm and an angle of beam convergence ϑ of 2 mrad.
