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Spring 2008 Seminar Series
Friday, April 4, at 3:30 p.m.
Room 264 MacQuigg Labs
Elaine D. Haberer
Postdoctoral Fellow
California NanoSystems Institute
University of California-Santa Barbara
A Merging of Materials and Device Perspectives through Fabrication and Assembly: GaN Microdisks and Bio-Templated Photovoltaic Materials
Abstract
Today, two strategies exist for electronic and optoelectronic device fabrication: a top-down approach and a bottom-up approach. The top-down paradigm is based on conventional microfabrication techniques developed over decades by the Si-based integrated circuits industry. These well-established, precision processes create devices by alternately building up and carving away material. Conversely, the bottom-up paradigm typically uses nanoscale building blocks which self-assemble, usually hierarchically, into larger scale structures, mimicking assembly in the natural world. Together these two approaches have the capability to realize specific material properties and device requirements at the both the nano- and micro- meter scale. These methods are most effective when leveraging an expertise in both materials properties and device design. As examples, the development of a GaN-based microdisk laser and low-cost bio-templated photovoltaic materials will be discussed.
The microdisk is a simple, circular optical cavity which is ideal for studying lasing phenomena in a material system such as GaN in which high quality in-plane and vertical epitaxial mirror formation is frustrated by hetero-epitaxial growth and lattice mismatch induced strain. However, the undercut geometry necessary to create the mushroom-shaped cavity typical of microdisks is non-trivial in the III-nitride material system because of its generally chemically inert nature and polarization. In order to fabricate the device using bandgap-selective photoelectrochemical etching, a complete understanding of material growth limitations, internal polarization fields, and band structure was required.
From the device perspective, practical photovoltaic materials must both efficiently absorb the solar spectrum and effectively separate and collect the photogenerated carriers. This is a challenging task for even well-studied conventional semiconductor materials. However, if the additional constraint of economical or low-cost manufacturing is applied, very few material choices currently exist. In order to address these device requirements, a bio-templated nanoscale system was designed to control macroscopic materials properties. Nanostructured films using CdSe nanoparticles as the photo-active material and Au nanoparticles to enhance film conductivity were fabricated.
As shown through these examples, when combined with insights from both device and materials perspectives, top-down and bottom-up paradigms jointly provide potentially limitless opportunities for novel, multifunctional materials and devices.
Bio
Elaine Haberer is currently a postdoctoral fellow in the California NanoSystems Institute at the University of California, Santa Barbara. She received both her B.S. and M.S. degrees in materials science from MIT, and her Ph.D. degree, also in materials science, from the University of California, Santa Barbara. HabererŐs current research interests include novel microfabrication and bio-templating techniques for the development of multifunctional materials and devices.
Please join our speaker for light refreshments in 479 Watts Hall following the talk.
