Electrical Characterization of Integrated InAs Nano-Structures
Sammanfattning: This thesis analyzes the electrical properties of InAs nano-structures, that are integrated into different materials and geometries. The thesis describes integration related issues of InAs, the epitaxial synthesis of the InAs nano-structures and summarizes experimental techniques for analysis of electrical properties of the integrated structures. InAs thin films, nanowires and membranes are investigated to determine their electrical quality. The thin films (> 300 nm thick) are integrated onto GaAs substrates using overgrowth over the tungsten patterns. Such integration method allows varying the area of the surface pinning region within the material to measure the extent of this region in InAs. A carrier saturation is observed when the tungsten density is increased which allows determining the effective length of the surface pinning region to be under 400 nm. InAs nanowire capacitors are investigated to measure their doping density and doping profile. The capacitance of the nanowire capacitors exhibits non parabolic band behavior and a full depletion, in contrast to conventional MOS capacitors. The threshold voltage of the fully depleted nanowires is extracted to determine doping density and dopant distribution profile within a nanowire. It is shown that dopants incorporate preferentially at the nanowire surface and the surface doping concentration is higher than in the nanowire bulk. Also, capacitance transients are analyzed to show the presence of traps in the oxide. InAs metamorphic films are integrated onto GaSb buffer layer to evaluate the relation between the quality of the buffer layer and the InAs. It is observed, that metamorphic InAs membranes (23 nm thick) are highly resistive, while thicker membranes (90 nm thick) can be measured by Hall Effect measurements. The mobility of 90 nm membranes is found be 2700 cm^2/Vs, which indicates a loss of the metamorphic lattice. It is shown that the resistivity of thin membranes is highly sensitive to surface treatment.
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