Influence of electron irradiation on the electronic transport mechanisms during the conductive AFM imaging of InAs/GaAs quantum dots capped with a thin GaAs layer

摘要

We have used conductive atomic force microscopy (C-AFM) to study the electronic transport mechanisms through InAs quantum dots (QDs) grown by molecular beam epitaxy on an n-type GaAs( 001) substrate and covered with a 5 nm thick GaAs cap layer. The study is performed with a conductive atomic force microscope working inside a scanning electron microscope. Electric images can be obtained only if the sample is preliminarily irradiated with an electron probe current sufficiently high to generate strong electron beam induced current. In these conditions holes are trapped in QDs and surface states, so allowing the release of the Fermi level pinning and thus conduction through the sample. The electronic transport mechanism depends on the type of AFM probe used; it is explained for a metal (Co/Cr) coated probe and p-doped diamond coated probe with the aid of energy band diagrams. The writing ( charge trapping) and erasing (untrapping) phenomena is conditioned by the magnitude of the electron probe current. A strong memory effect is evidenced for the sample studied.