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 transmission electron microscopy. In both materials, indentation rosettes with approximate twofold symmetry form around the indents. In general, the rosettes consist of dislocations and microtwins. The rosette arms in n-type (001) GaSb are only slightly asymmetric along the two [110] directions, with the longer arms corresponding to alpha-type dislocations. This implies that the mobility of alpha-dislocations in GaSb is higher 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 half-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 mechanism for indentation twinning is proposed whereby the step created by surface nucleation of a dislocation half-loop acts as a preferential site for nucleation of the next half-loop on an adjacent {111} plane.