Microtwins and partial dislocations in GaAlAs alloys after indentation at room temperature: the effects of composition and doping

Microtwins and associated partial dislocations caused by microindentation, at room temperature, on {001} planes of GaAs and of ternary alloys containing up to 30% Al, have been studied by transmission electron microscopy. Both n-type and p-type alloys have been studied. It is shown that the twinning occurs on planes which converge or diverge below the indentation depending on the type of doping and the 〈110〉 direction along which the twins intersect the surface. The Burgers vectors of the partial dislocations involved in the twinning have been determined including their signs. In all cases the edge components of the dislocations are on the same side of the slip plane as the indentations. Using chemical etching of the {111} planes it is concluded that the mobilities of As(g) partial dislocations are greater than the mobilities of Ga/Al(g) dislocations in n-doped material whereas the reverse is true for p-doped material. In this way a completely consistent picture of microtwinning in these materials has been developed.