Generation and propagation of defects into molecular beam epitaxially grown GaAs from an underlying GaAs substrate

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Abstract
Dislocation and growth striation hereditability from liquid-encapsulated Czochralski (LEC) grown GaAs substrates to molecular beam epitaxially (MBE) grown epilayers is studied for the different types of epilayer structures including homo-, hetero-, and superlattice. Also the correlation of surface defects in the epilayers with dislocations in the substrates is studied. It is found that growth striation in the substrate is not inherited into the epilayer, whereas dislocation propagation strongly depends on the epilayer structure. Dislocation distributions in GaAs epilayers for homo- (GaAs/GaAs substrate) and hetero- (GaAs/Al0.3Ga0.7As or AlAs/GaAs substrate) structures inherit the dislocation distribution maps for their substrates. On the other hand, dislocation propagation can be effectively prevented by introducing an AlAs/GaAs superlattice spacer between the GaAs epilayer and the substrate. As for surface defects, micron-sized hillocks emerge when the superlattice structure is fabricated. Their morphological configurations are very similar to those of previously reported oval defects in MBE-grown GaAs layers. However, these newly found surface defects are apt to be generated by the shutter operation and this close correlation with the dislocations in the substrate is quite different from the usual oval defects.