Abstract
A TEM study of the plastic deformation around indentations made in Ga(1-x)A1xAs of various compositions ranging from x=0 to 0.3 i.e. 0 to 30%A1 is described in this work. The GaAlAs examined was in the form of capping layers grown on the {001} face of GaAs substrates. The indentations were made with a load of 5g at room temperature using a Vickers diamond indenter with its diagonals parallel to the directions. Slip dislocations and microtwins were seen around the indentations in the TEM. The slip dislocations extend far into the crystal whereas the microtwinning is concentrated closer to the indentation. The occurrence of microtwinning has been found to be more dependent on the type of doping rather than the Al concentration. In n-doped crystals microtwinning occurs asymmetrically around the indentations where as when p-doped they occur more symmetrically. For n- and p-doping the leading twinning dislocations are As(g) and Ga(g) respectively. In n-doped GaAlAs microtwinning occurs predominantly on slip planes that converge under the indent. In p-doped GaAlAs microtwinning occurs on both converging and diverging slip planes. All the microtwins are formed from intrinsic overlapping stacking faults.