Surface modification of III-V nanostructures studied by low-temperature scanning tunneling microscopy

In the past decade, driven by the demand for materials with high performance for next-generation semiconductor devices (e.g., for quantum computing), the exploration of III-V semiconductor materials and the design of improved devices based on these materials has extended to the nanometer scale, with several highlights in the studies of quantum wells, quantum dots, and nanowires (NW) in recent years. On the path of seeking smaller scale devices, the lateral scale is usually limited by the spatial resolution of the lithographic processes. Now, the challenge lies in the combination of semiconductor nanoscale structure with the desired electronic properties. Scaling down material synthesis to crystalline structures of only few atoms in size and precisely positioned in device configuration has not been realized so far. Moreover, the compatibility for large-scale industrial device processing is also challenging.
In this dissertation, I present the surface characterization and studies of the modification of nanostructures on III-V semiconductor surfaces, with the techniques of low temperature scanning tunneling microscopy/spectroscopy (LT-STM/S) and X-ray photoelectron spectroscopy (XPS). Two main topics are Bi incorporation in GaAs (and InAs) surfaces and self-driven formation of nanostructures with atomic-scale precision. Different zinc blende and wurtzite crystal planes have been investigated, including the {11-20}- type facet which for GaAs and InAs uniquely exists on the side walls of NWs and nanoplatelets. The utilization of the tailored facets of NWs as templates for Bi-induced nanostructure formation has been explored as well.
Bi-introduced low-dimensional nanostructures and exotic electronic states in III-V semiconductor systems have been investigated. The covalent bonds of Bi atoms in the self-formed Bi nanostructures on III-V substrates can vary depending on the substrate template and preparation condition, such as the Ga-Bi bonds in the 1D chain and 2D island nanostructures on Wz{11-20}-type facets on GaAs NWs. The possibility of tuning the self-formed III-V:Bi nanostructures in a more controllable way has been explored in this thesis. A significant high coverage of Bi on III-V semiconductor surface has been achieved. The observed variable bandgap and Bi-induced surface states are promising for applications in surface bandgap engineering and quantum technology components.