Self-organized InGaAs quantum dots grown on GaAs (3 1 1)B substrate studied by conductive atomic force microscope technique

Abstract

We have used conductive atomic force microscope (AFM) in a high vacuum in order to investigate the electronic properties of self-organized In x Ga 1– x As quantum dots (QDs) on GaAs (3 1 1)B substrates. The QDs were fabricated by atomic H-assisted molecular beam epitaxy, and Si AFM tips coated with Au, which warrants electrical conductivity were used to measure both the topographic and current images of QDs surface simultaneously. The conductive AFM measurements were performed in vacuum at room temperature and at lowered temperatures. With this technique, the current–voltage ( I– V) characteristics of QDs of varying sizes, and of any other arbitrary positions on the QDs surface can also be studied by using the same conductive AFM tip. It was found that the center of a QD is more conductive than its periphery, and the surface in between the QDs is highly resistive. The differences in the conductance are thought to be due to the local modification of surface bending associated with the surface states. Further, we have shown that the conductance becomes spatially uniform at all points over the packed and ordered QDs at low temperatures, which could be explained by lateral coupling of these strained QDs.