STM topographic and barrier imaging of self-assembled InAs/GaAs dots

In this paper we present scanning tunneling microscopy (STM) images of self-assembled InAs dots on GaAs(001) surfaces. The STM was operating in air at room temperature using both constant-current as well as gap-modulated modes. The conductivity and surface band bending have been modified by irradiating the surface by an Ar+ laser beam during the scan. In this manner, photoconductivity images have been obtained in an attempt to have a contrast between the dots and the InAs wetting layer. Our results reveal a clear difference between STM topographies and ‘barrier’ method. While topographic images show dome-shaped dots, the barrier ones resemble sharp pyramids even if they are acquired on the same place and at the same time. The generation of STM images is considered for both modes of operation and the concepts of topography and barrier height √ϕ are revised and compared with a numerical simulation of Qdot surfaces.