When 12:00 PM - 2:00 PM Sep 15, 2016
Where 3158 H.H. Dow
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Manipulating Surface Energy to form Compound Semiconductor Nanostructures


Matt DeJarld
Thesis Defense

Nanostructures have been lauded for their quantum confinement capabilities and potential applications in future devices. Compound semiconductor nanostructures are being integrated into the next generation of photovoltaic and light emitting devices to take advantage of their unique optical characteristics. Despite their promise, adoption of nanostructure based devices has been slow. This is due in large part to difficulties in effective fabrication and processing steps. By manipulating the surface energy of various components during growth, we can control the final structure and corresponding optoelectronic characteristics. Specifically I will present on GaSb quantum dots embedded in GaAs and GaAs nanowires using novel substrate and catalyst materials.

 

GaSb quantum dots embedded in a GaAs matrix are ideal for devices that require capture of minority carriers as they exhibit a type II band offset with carrier concentration in the valence band. However, during GaAs capping, there is a strong driving force for the dot to demolish into a distribution of intact dots, rings, and GaSb material clusters. We demonstrate the ability to mitigate this effect using both chemical and kinetic means: we alter the surface chemistry via the addition of aluminum, and use droplet epitaxy as an alternative quantum dot formation method. Secondly, the growth of high quality GaAs on silicon has always been restricted due to material incompatibilities. With the emergence of increasingly smaller low power electronics, there is a demand to integrate optoelectronic devices directly on the surface of CMOS sensor stacks. Utilizing the vapor-liquid-solid growth mechanism we are able to demonstrate the growth of high quality GaAs nanowires on polycrystalline substrates at low temperatures. This allows for the growth of III-V nanowire based devices directly on the metal pads of pre-packaged CMOS chips. We also investigate the potential use of bismuth as an alternative to gold for catalyzing nanowire growth.