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

Abstract

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.

Investigating the Composition and Conductance Distributions on Highly GeSi Mixed Quantum Dots and Inside Oxidation Problem

“…2a – h , respectively. Before NHH etching, ring-shaped and cross-shaped current distributions are observed on dome and pyramid QDs, respectively, similar to the results reported in our previous papers [ 31 , 32 ]. For simplicity, only the dome-shaped QDs will be concerned afterwards, as the result is similar for pyramid-shaped QDs.…”

“…To get the QDs’ electrical properties, measurement on single QDs is particularly important as it can exclude the averaging effect. Therefore in recent years, scanning probe microscopy (SPM)-based techniques have been attempted to investigate the electrical properties on single QDs [ 23 – 32 ]. Among these techniques, conductive atomic force microscopy (CAFM) is mostly often applied.…”

“…Among these techniques, conductive atomic force microscopy (CAFM) is mostly often applied. The conductive properties of individual InAs, InGaAs, and GeSi QDs have already been achieved by CAFM [ 27 – 32 ]. However, the combined studies on the QDs’ composition distribution and their electrical properties are still lacking, and thus the correlations between these two characteristics are not clear yet.…”

Composition and conductance distributions of single GeSi quantum rings studied by conductive atomic force microscopy combined with selective chemical etching

“…Among these techniques, conductive atomic force microscopy (CAFM), which can investigate the conductive properties of individual quantum structures, is most often used. In recent years, the conductance distributions of various quantum structures have been obtained [19][20][21][22][23][24]. In the case of QRs, CAFM has also been applied to investigate the conductance distributions of InAs QRs [25] and the conductive property change during the transformation from GeSi QDs to QRs by Si capping [26].…”

Increased conductance of individual self-assembled GeSi quantum dots by inter-dot coupling studied by conductive atomic force microscopy

“…The large increase of QDs’ conductance at large biases should be an exciting result, as it suggests that the coupled QDs’ conductive properties can be greatly regulated by bias voltage, which should be valuable for applications. The bias dependence of the conductance of individual QDs has been investigated in our previous paper [27]. It was found that the QDs’ current increases much faster with the bias than the wetting layer, which was attributed to the discrete energy levels of QDs.…”