Bias-dependent conductive characteristics of individual GeSi quantum dots studied by conductive atomic force microscopy.

The bias-dependent electrical characteristics of individual self-assembled GeSi quantum dots (QDs) are investigated by conductive atomic force microscopy. The results reveal that the conductive characteristics of QDs are strongly influenced by the applied bias. At low (-0.5 to - 2.0 V) and high (-2.5 to - 4.0 V) biases, the current distributions of individual GeSi QDs exhibit ring-like and disc-like characteristics respectively. The current of the QD's central part increases more quickly than that of the other parts as the bias magnitude increases. Histograms of the magnitude of the current on a number of QDs exhibit the same single-peak feature at low biases, and double- or three-peak features at high biases, where additional peaks appear at large-current locations. On the other hand, histograms of the magnitude of the current on the wetting layers exhibit the same single-peak feature for all biases. This indicates the conductive mechanism is significantly different for QDs and wetting layers. While the small-current peak of QDs can be attributed to the Fowler-Nordheim tunneling model at low biases and the Schottky emission model at high biases respectively, the large-current peak(s) may be attributed to the discrete energy levels of QDs. The results suggest the conductive mechanisms of GeSi QDs can be regulated by the applied bias.