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Scanned probe characterization of semiconductor nanostructures


Advances in the synthesis of materials and device structures have accentuated the need to understand nanoscale electronic structure and its implications. Scanning probe microscopy offers a rich variety of highly spatially accurate techniques that can further our understanding of the interactions that occur in nanoscale semiconductor materials and devices. The promising nitride semiconductor materials system suffers from perturbations in local electronic structure due to crystallographic defects. Understanding the electronic properties and physical origin of these defects can be invaluable in mitigating their impacts or eliminating them all together. In the second chapter of this dissertation, scanning capacitance microscopy (SCM) is used to characterize local electronic structure in a-plane n-type gallium nitride. Analysis reveals the presence of a linear, positively charged feature aligned along the direction which likely corresponds to a partial dislocation at the edge of a stacking fault. In the third chapter, conductive atomic force microscopy is used to determine the effects of Ga/N flux on the conductive behavior of reverse-bias leakage paths in gallium nitride grown by molecular beam epitaxy (MBE). Our data reveal a band of fluxes near Ga/N ̃ ̃1 for which these pathways cease to be observable. These observations suggest a method for controlling the primary source of reverse-bias Schottky contact leakage in n-type GaN grown by MBE. A deeper understanding of the interaction between macro-scale objects and nanoscale electronic properties is required to bring the exciting new possibilities that semiconductor nanowires offer to fruition. In the fourth chapter, SCM is used to examine the effects of micron-scale metal contacts on carrier modulation and electrostatic behavior in indium arsenide semiconductor nanowires. We interpret a pronounced dependence of capacitance spectra on distance between the probe tip and nanowire contact as a consequence of electrostatic screening of the tip-nanowire potential difference by the large metal contact. These results provide direct experimental verification of contact screening effects on the electronic behavior of nanowire devices and are indicative of the importance of accounting for the effect of large-scale contact and circuit elements on the characteristics of nanoscale electronic devices

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