Direct detection of electronic states for individual indium arsenide (InAs) quantum dots grown by molecular beam epitaxy

Indium arsenide (InAs) quantum dots (QDs) have been characterized using a conductive-mode atomic force microscope (C-AFM), where a well-defined gold-coated AFM probe has been used to electrically probe each individual QD. The InAs QDs were grown on a gallium arsenide (GaAs) substrate in a self-assembled manner by using molecular beam epitaxy (MBE). The measured current-voltage (I-V) curves of individual QDs exhibit a typical Schottky diode behavior, which can be attributed to the metal/semiconductor junction between the AFM gold probe and the n-doped GaAs bulk. However, distinct I-V curves are observed in sequential measurements, where a less forward turn-on voltage is measured in the subsequent voltage sweeps compared to the initial sweep. However, this effect is not evident when the same measurements are conducted on a plane surface (in the absence of QDs) on the same substrate. The discrete voltage values at the forward bias on a QD indicates a change in the electronic states due to trapped electrons in the QD during the initial voltage sweep. These unique characteristics of QDs can be exploited for potential applications in fast-response data storage devices and quantum computing.