In-situ Growth of Sn-seeded GaAs and GaSb Nanowire Heterostructures

Sammanfattning: One of the ways to utilize III-V nanowires, is to make use of the possibility to combine materials and create heterostructures which allows for creating material combinations with new properties. A special interest can be taken into Sb-containing nanowires due to the high electron mobility, however there has been reported difficulties with switching to other materials because of a 'memory effect' where Sb lingers in the system and nanowire. Moreover, there is a need for exploring different seed materials such as Sn for nanowires since the commonly used Au can introduce problems in Si-integrated devices. In this thesis, the primary focus was to create heterostructure nanowires of Sn-seeded GaSb and GaAs and try to optimize the transitions by growing nanowires while studying them in an Environmental Transmission Electron Microscope. When growing with GaAs, a twin superlattice structure was detected at a lower V/III ratio versus at a higher V/III ratio where the nanowire grew straight zincblende. This trend seems to coincide with ex-situ work with Sn-seeded GaAs and is exciting since twins can perhaps indicate a possibility for wurtzite to form. Moreover both GaAs-GaSb and GaSb-GaAs were grown and after observing suboptimal switches, such as with substantial overgrowth or kinking, speculations were made as to why these phenomena occurred. These insights helped with the succeeding growth of GaSb-GaAs-GaAsSb heterostructures. For the GaSb-GaAs switch, the ability to switch to pure GaAs was an intriguing discovery as there has not been any record of this before. However the transitions in the GaSb-GaAs-GaAsSb heterostructure observed were gradual, and for the first switch (GaSb-GaAs) the nanowire kinked and in the second switch (GaAs-GaAsSb) As never fully left the nanowire crystal. This work has contributed to the understanding of the different roles the parameters play in terms of affecting the GaAs and GaSb heterostructure nanowire growth, but also laid a foundation for future research.