Correlating the nanostructure and electronic properties of InAs nanowires

The electronic properties and nanostructure of InAs nanowires are correlated by creating multiple field effect transistors (FETs) on nanowires grown to have low and high defect density segments. 4.2 K carrier mobilities are ~4X larger in the nominally defect-free segments of the wire. We also find that dark field optical intensity is correlated with the mobility, suggesting a simple route for selecting wires with a low defect density. At low temperatures, FETs fabricated on high defect density segments of InAs nanowires showed transport properties consistent with single electron charging, even on devices with low resistance ohmic contacts. The charging energies obtained suggest quantum dot formation at defects in the wires. These results reinforce the importance of controlling the defect density in order to produce high quality electrical and optical devices using InAs nanowires.Comment: Related papers at http://pettagroup.princeton.ed

Mechanism of periodic height variations along self-aligned VLS-grown planar nanostructures

In this study we report in-plane nanotracks produced by molecular-beam-epitaxy (MBE) exhibiting lateral self-assembly and unusual periodic and out-of-phase height variations across their growth axes. The nanotracks are synthesized using bismuth segregation on the GaAsBi epitaxial surface, which results in metallic liquid droplets capable of catalyzing GaAsBi nanotrack growth via the vapor–liquid–solid (VLS) mechanism. A detailed examination of the nanotrack morphologies is carried out employing a combination of scanning electron and atomic force microscopy and, based on the findings, a geometric model of nanotrack growth during MBE is developed. Our results indicate diffusion and shadowing effects play significant roles in defining the interesting nanotrack shape. The unique periodicity of our lateral nanotracks originates from a rotating nucleation “hot spot” at the edge of the liquid–solid interface, a feature caused by the relative periodic circling of the non-normal ion beam flux incident on the sample surface, inside the MBE chamber. We point out that such a concept is divergent from current models of crawling mode growth kinetics and conclude that these effects may be utilized in the design and assembly of planar nanostructures with controlled non-monotonous structure

IDST 190-007 Blurb

Blurb from IDST 19

Nanoscale Crystal Growth: The Importance of Interfaces and Phase Boundaries Kristallväxt på Nanometer Skala: Vikten av Ytor och Gränser

Surfaces and interfaces have a special significance to nanotechnology because the surface/volume ratio of nanomaterials is larger than for bulk materials. Therefore, interfaces of nanomaterials are usually more important to the properties of nanomaterials than for larger scale materials. Furthermore, crystal growth occurs at the interfaces between the growing crystals and the supply media. An understanding of the interfaces is therefore essential to understanding growth. Nanoscale crystal growth of three, two, and to some extent one-dimensional crystals has been explained in the context of crystalline interfaces. This understanding has helped improve production of nanostructures and devices that are both scientifically and commercially beneficial. This dissertation expands on the importance of interfaces and atomistic processes occurring at these interfaces; explaining the growth and control of different nanocrystals. A brief review of crystal growth terminology and theory is given. A new technology recently developed to produce compound semiconductor quantum dots is described within the context of the interfaces involved. The majority of the dissertation will focus on explaining and understanding growth of one-dimensional nanostructures, called nanowires, grown in a three-phase system. The currently accepted growth mechanism for nanowires of this type is the vapor-liquid-solid (VLS) mechanism. The VLS and similar mechanisms lack details about the atomistic processes involved in wire growth. When these atomistic processes are examined, it is revealed that there are several different names describing what are proposed to be ?different? mechanisms that in reality rely on the same atomistic processes. The key to understanding nanowire growth lies in understanding the atomistic processes occurring at the interfaces. Due to the fundamental similarities in the mechanisms with different names, the name ?Preferential Phase-Boundary Nucleation? (PPBN) is suggested as a replacement for the many different names. Unlike previous names this name is relevant to the processes as well as emphasizing the importance of the phases and the interfaces. A better understanding of interfaces and the processes that occur at them leads to a greater understanding and control of the growth of crystalline nanostructures