Formation of edge misfit dislocations in GexSi1−x(x∼0.4–0.8) films grown on misoriented (001)→(111) Si substrates: Features before and after film annealing

Abstract

The dislocation structure at the initial stage of relaxation of GexSi1−x films (x∼0.4–0.8) grown on Si(001) substrates tilted at 6° to the nearest (111) plane is studied. One of the directions along which edge dislocations are formed is no longer in the plane of the interface but crosses the latter at the angle of miscut. Therefore, long edge misfit dislocations (MDs) cannot exist in the direction of substrate misorientation, because their ends move away from the interface during dislocation propagation. Two different mechanisms of formation of short segments of edge (90°) MDs in the direction of substrate misorientation are found. The first mechanism is the correlated nucleation of complementary 60° dislocation half-loops manifested in the form of the so-called Y-center consisting of a short segment of the 90° MD and 60° MDs diverging from this segment in form of two rays in the miscut direction. In the second mechanism, the 90° MD segment is formed owing to intersection of already existing complementary 60° MDs slipping in mirrorlike inclined planes {111}. Samples annealed at higher temperatures contain MD segments, which lose their contrast on one of the TEM images taken to detect edge dislocation segments in the two-wave diffraction mode but do not coincide with the direction [110] (they pass along the intersections of the mirrorlike inclined planes {111} with the surface of the misoriented Si substrate). To explain this phenomenon, a model is proposed, where one of the pair of complementary 60° MDs propagating at an angle to each other continuously approaches the other by the cross-slip mechanism. Formation of a chain of edge MD segments connected by a pair of 60° MDs becomes possible. The averaged direction of such a dislocation structure coincides with the direction of one of the 60° MDs.