Depth-resolved cathodoluminescence in GaAs epilayers grown on Si substrates

Cathodoluminescence is used to study defects in undoped GaAs epilayers grown on Si. The GaAs epilayers include in situ thermal cycle (TC) processes and/or InGaAs-GaAs strained-layer superlattices (SLS's). In an in situ TC sample, the density of dark-spot defects is proved to increase with electron beam energy. Under the condition that the electron beam penetration depth reaches the position of the in situ TC, weak crosshatching contrasts appear, which are thought to be due to the movement and arrangement of 60°-type dislocations along the {111} planes during thermal cycle processes. In the sample with an in situ TC followed by SLS growth, distinct dark nonradiative recombination lines along directions appear in the luminescence image of the top GaAs layer. These aligned dark lines are thought to be caused by dislocations lying near the SLS/GaAs interface.