Effects of a native oxide layer on the conductive atomic force microscopy measurements of self-assembled Ge quantum dots

摘要

The electrical properties of self-assembled Ge quantum dots were investigated by using conductive atomic force microscopy (CAFM). It was found that the conductive properties of quantum dots were strongly affected by the native oxide layer formed on the quantum dots. With the existing oxide layer, the current-voltage curves of the quantum dots obviously depended on the applied normal forces, and all the curves could be well fitted by the Fowler-Nordheim tunnelling model by changing the oxide layer thicknesses. After the oxide layer was removed by HF etching, the current-voltage characteristics could be well explained by the Schottky emission model. But when the etched sample was exposed to air for more than 150 min, its current-voltage behaviour returned back to that before the etching. Despite the significant effects of the oxide layer on the current-voltage characteristics, the current distributions of individual quantum dots remained almost the same for different thicknesses of the oxide layer or different normal forces applied. Therefore, the effects of the oxide layer on the current distribution can be ignored, though the absolute current values were strongly affected. Our results thus provide important evidence for the reliability of CAFM measurements in ambient conditions.