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

Abstract

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