A STUDY OF THE DEFECT STRUCTURE IN GAAS-LAYERS GROWN AT LOW AND HIGH-TEMPERATURES ON SI(001) SUBSTRATES

In this work we report the defect structure of GaAs layers grown on Si (001) substrates by atomic layer molecular beam epitaxy at 350 degree s C and conventional molecular beam epitaxy at 580 degrees C, investig ated by transmission electron microscopy. It is found that the GaAs la yers grown at 580 degrees C show high threading dislocation densities, whilst the majority defect types in the GaAs layers grown at 350 degr ees C are stacking faults and microtwins. These results can be explain ed by taking into account that the mobility of partial dislocations de pends on both the stress in the epitaxial layer and the growth tempera ture. According to this dependence, a transition from dissociated thre ading dislocations at a low temperature (350 degrees C) to perfect thr eading dislocations at a high temperature (580 degrees C) can be expec ted.