INDENTATION-INDUCED DISLOCATIONS AND MICROTWINS GASB AND GAAS

The {100} and {110} faces of n-type GaSb and the {110} face of n-type GaAs have been indented at room temperature and 200 degrees C, and the plastic zone around the microindents has been investigated by transmi ssion electron microscopy. In both materials, indentation rosettes wit h approximate twofold symmetry form around the indents. In general, th e rosettes consist of dislocations and microtwins. The rosette arms in n-type (001) GaSb are only slightly asymmetric along the two [110] di rections, with the longer arms corresponding to alpha-type dislocation s. This implies that the mobility of alpha-dislocations in GaSb is hig her than the mobility of beta dislocations. In both GaSb and GaAs, the 90 degrees perfect and partial dislocations have the highest mobility . Based on the experimental results, it is proposed that, in both GaSb and GaAs, perfect dislocations nucleate on the identation facets as h alf-loops with Burgers vectors parallel to the propagation directions of the rosette arms. On the other hand, twinning dislocations nucleate on the indentation surface as partial dislocation half-loops. A mecha nism for indentation twinning is proposed whereby the step created by surface nucleation of a dislocation half-loop acts as a preferential s ite for nucleation of the next half-loop on an adjacent {111} plane.