Studying the lateral composition in Ge quantum dots on Si(0Â 0Â 1) by conductive atomic force microscopy

Conductive atomic force microscopy (C-AFM) has been employed to investigate the distribution of the lateral composition in Ge quantum dots (QDs) grown by molecular beam epitaxy on p-type Si(0 0 1) substrate. Since the different conductivity of the components (Ge and Si) in the Ge QDs results in different current signals, it is then possible to obtain the information of composition distribution from the current images. We have investigated two types of samples grown at 550 °C and 640 °C, respectively, and found that the conductance distribution of these two types of QDs were significantly different. This difference can be attributed to the different degrees of Si alloying into the Ge QDs at different growth temperatures. Our results demonstrate that the dome-shaped QDs grown at the higher temperature are Si-Ge alloys with Si composition >35% at most part of the QD, while the QDs with the same shape grown at the lower temperature show high Ge distribution (>65%) in the whole dot, which are supported by the selective etching experiments.