Abstract
The conductive properties of individual self-assembled GeSi quantum dots (QDs) are investigated by conductive atomic force microscopy on single-layer (SL) and bi-layer (BL) GeSi QDs with different dot densities at room temperature. By comparing their average currents, it is found that the BL and high-density QDs are more conductive than the SL and low-density QDs with similar sizes, respectively, indicating the existence of both vertical and lateral couplings between GeSi QDs at room temperature. On the other hand, the average current of the BL QDs increases much faster with the bias voltage than that of the SL QDs does. Our results suggest that the QDs’ conductive properties can be greatly regulated by the coupling effects and bias voltages, which are valuable for potential applications.
Highlights
Self-assembled semiconductor quantum dots (QDs) have been intensively studied over past decades due to their great importance for both fundamental physics and device applications [1,2,3]
The topographic images of GeSi QDs were obtained by AFM in tapping mode, while their conductive properties were measured by conductive atomic force microscopy (CAFM) in contact mode
Both large QDs of 50 ~ 70 nm in diameter and small QDs of 30 ~ 50 nm in diameter are observed on samples A/B, except that the density of the large QDs on sample B is higher than that on sample A
Summary
Self-assembled semiconductor quantum dots (QDs) have been intensively studied over past decades due to their great importance for both fundamental physics and device applications [1,2,3]. As the efficiency of single-layer QDs is relatively low, vertically aligned multilayer QDs are often adopted for practical applications [3,4,5,6]. By repeating dot layers separated by spacer layers with a few nanometers in thickness, a more homogeneous size distribution could be achieved, simultaneously with novel physical properties induced by coupling [7,8]. The coupling effects between the vertically aligned QDs have been investigated by various macroscopic techniques such as photoluminescence (PL) and admittance spectroscopies [6,8,9,10,11,12,13], which are found to be strongly dependent on the thickness of the spacer layer.
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