An STM-based study of Bi deposition on InAs(110)

Abstract: III-V semiconductor compounds containing Bi, such as InBi, have recently attracted much attention due to predictions of band inversion and topological insulators. The predictions showed that films of InBi could be applicable in quantum computers and at room temperature. The common approach of realizing such a structure, by growing InAsBi films, has not been successful, as the Bi content has been far too low for the properties of interest to emerge. The work presented in this thesis explores an alternative approach to forming the InBi films – with a clean InAs(110) sample as a starting point. Bi is deposited onto the sample via thermal evaporation, keeping the sample at room temperature. If successful, the Bi atoms are believed to undergo an exchange process where they replace the exposed As atoms in the lattice. This would, in turn, enable us to facilitate a higher and more homogeneous Bi incorporation as well as providing an atomically sharp interface between the top layer and the rest of the substrate. The main goal was, therefore, to determine whether the Bi atoms would be incorporated into the host lattice via the Bi-for-As exchange process, or if they would be desorbed and leave the surface. The idea of the exchange process is supported by the previous work on Sb deposition on GaAs and InAs nanowires. The InAs(110) sample, and the effect of the Bi deposition approach, was studied by scanning tunneling microscopy (STM). By studying the STM images taken, it became evident that the deposited Bi atoms formed monolayer high islands that had a larger rectangular structure than the underlying substrate. Furthermore, the unit cell of the Bi structure was rotated 35.4° clockwise relative to the InAs(110) unit cell. The different structure, as compared to the substrate, indicated that the islands were metallic Bi. After the Bi deposition, the InAs(110) sample was annealed. However, with only STM to study the sample, it was difficult to tell whether most of the Bi atoms were desorbed from the surface, exposing a much rougher InAs(110) surface, or, if the Bi had been incorporated either as InBi or InAs_(x)Bi_(1−x).