In-situ Study of the Growth, Composition and Morphology of III-V Semiconductor Nanowires

• It is widely known that nanoparticle seeded growth of III-V semiconductor nanowires often occurs via the vapor-liquid-solid mechanism. However, conventional growth of nanowires is carried out in closed systems, where mostof the details and dynamics of the growth are impossible to follow. Since all analysis is typically carried out after growth completion and transfer, only the trends in the produced growth series give hints to the processes occurringat the nanoscale.In this thesis, the growth of Au-seeded III-V semiconductor nanowires has been studied in-situ, during growth, by means of environmental transmission electron microscopy. The supply of growth species in the form of precursormolecules directly into the microscope column provides a unique opportunity to follow the nanowire growth while it is occurring, through all techniques commonly available in a transmission electron microscope. This means that nanoscale growth dynamics can be studied in real time under static or changing growth conditions, and changes in crystal structure, composition and morphology can be revealed.The present investigation highlights the relation between the liquid nanoparticle and the solid nanowire. For GaSb nanowires, I show that the nanoparticle can swell by alloying to various extents with Ga, which will influence the formed nanowire diameter. I also investigate the compositional relationship between the Au-based nanoparticles and growing ternary InGaAs nanowires, where it is established that the solidified composition is dependent on both kinetics and thermodynamics. One of the main conclusions is that a high concentration of indium in the nanoparticle is needed in order to form indium rich solid InGaAs. The in-situ investigations reveal that nanowire growth is dynamic, and the layer-by-layer growth process consists of separate steps of material collection (incubation) and solidification (step-flow). I present how the layer-by-layer growth is affected by changes in the precursor flows for GaSb nanowires, and how the formation of defects in GaAs affects growth rate and can influence the growth behavior. Finally, I discuss the multilayer growth phenomenon in InGaAs nanowires, where multiple layers nucleate and grow simultaneously at the liquid-solid interface. In many cases the results are compared to simulations and models, which can be used to provide a more detailed understanding about the factors influencing the growth. The results presented in this thesis provide fundamental insight into the growth of nanostructures and are expected to be useful in the continued pursuit of atomic scale control.

Ämnesord

NATURVETENSKAP  -- Kemi -- Materialkemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Materials Chemistry (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Nanoteknik -- Nanoteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Nano-technology -- Nano-technology (hsv//eng)

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

Nyckelord

Nanowire

Semiconductor

III-V

Transmission Electron Microscopy

In-situ

Environmental TEM

Crystal growth

Publikations- och innehållstyp

dok (ämneskategori)

vet (ämneskategori)