As technology journalist David Pogue recounted, “If everything we own had improved over the last 25 years as much as electronics have, the average family car would travel four times faster than the space shuttle; houses would cost 200 bucks.”
The electronics industry is one which, through Moore’s Law, created a self-fulfilling prophecy of exponential advancement. This progress has made unforeseen technologies commonplace and revealed new physical understanding of the world in which we live. It is in keeping with these trends that the current work is motivated. This dissertation focuses on the advancement of electrical and optoelectronic characterization techniques suitable for understanding the underlying physics and applications of nanoscopic devices, in particular semiconducting nanowires and nanotubes.
In this work an in situ measurement platform based on a field-emission scanning electron microscope fitted with an electrical nanoprobe is shown to be a robust instrument for determining fundamental aspects of nanowire systems (i.e. the dominant mode of carrier transport and the nature of the electrical contacts to the nanowire). The platform is used to fully classify two distinct systems. In one instance it is found that indium arsenide nanowires display space-charge-limited transport and are contacted Ohmically. In the other, gallium arsenide nanowires are found to sequentially show the trap-mediated transport regimes of Poole-Frenkel effect and phonon-assisted tunneling. The contacts in this system are resolved to be asymmetric – one is Ohmic while the other is a Schottky barrier.
Additionally scanning photocurrent microscopy is used to spatially resolve optoelectronic nanowire and nanotube devices. In core/shell gallium arsenide nanowire solar cell arrays it is shown that each individual nanowire functions as a standalone solar cell. Nanotube photodiodes are mapped by scanning photocurrent microscopy to confirm an optimal current collection scheme has been realized and to locate the devices’ most responsive region. The devices are shown to exhibit strongly enhanced photocurrent under reverse bias proposing unexpected efficiency increases in a scalable device layout.
|Advisor:||Islam, M. Saif|
|Commitee:||Horsley, David A., Leonard, Francois|
|School:||University of California, Davis|
|Department:||Electrical and Computer Engineering|
|School Location:||United States -- California|
|Source:||DAI-B 73/01, Dissertation Abstracts International|
|Subjects:||Electrical engineering, Nanoscience, Nanotechnology|
|Keywords:||Charge transport, Nanoprobes, Nanotubes, Nanowires, Photodetectors, Scanning photocurrent microscopy|
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