High resolution imaging of GaAs nanowires

Abstract: Semiconductor nanowires (NWs) are expected to be the new building blocks in electronics and photonics, but improved understanding of the nanowire surfaces and electronic properties are required to realize it. In this bachelor thesis, wurtzite (Wz)-zincblende (Zb) axial heterostructure GaAs nanowires are studied using scanning tunneling microscopy and spectroscopy. The hexagonal cross section nanowires have {110}- type side facets for the Zb top part and {10-10}- type side facets for the Wz bottom part . Additionally {11-20}-type facets and {111}B- type facets are present at the transition between the two crystal structures. The surfaces of these facets are investigated to characterize their morphology and defects. The {110}-type zincblende facets are characterized by 60-80 nm wide terraces with wavy edges. At least one type of point defects is observed on the surface, which is thought to be Arsenic mono-vacancies with a density of the order 〖10〗^12-〖10〗^13 cm^(-2). No stacking faults or twin-planes are observed in the zincblende crystal structure, but are seen in the crystal transition region between the two crystal structures. A downward directed, 5-15 nm wide stripe-like overgrowth structure is seen on the {11-20}-type wurtzite facets. Furthermore, 50-70 nm wide {10-10}-type facets show a morphology of atomic steps occurring perpendicular to the nanowire growth direction. A 5-15 nm wide structure, parallel the nanowires are observed to emanate from these atomic steps. The surfaces of the wurtzite part of the nanowires have almost no point defects, but show a low density of stacking fault.