Doctoral Dissertation | Jason Kendrick Marmon
Event Date:
May 3, 2016 – 2:00 PM to May 4, 2016 – 1:59 PM
Location:
Grigg 131
Event Date:
May 3, 2016 – 2:00 PM to May 4, 2016 – 1:59 PM
Location:
Grigg 131
Ph.D Nanoscale Science
Doctoral Dissertation Presentation
Jason Kendrick Marmon
Doctoral Advisor: Dr. Yong Zhang
“Light Powered Electronic-Optical Devices: Extrinsic and
Intrinsic Properties of II-VI Semiconductor Nanowires”
Abstract:
Modern electronics are developing electronic-optical integrated circuits, while their electronic backbone, e.g. field- effect transistors (FETs), remains the same. However, further FET down scaling is facing physical and technical challenges, and physical limitations are expected to end FET contributions to Moore’s law by the end of the next decade (c.a. the
2020s). This dissertation explores a novel computing technology that is based on a fundamentally different mechanism than found in FETs, which is termed a light–effect transistor (LET), yet it is more practical and viable than other future
generation technologies currently being developed. A light–effect transistor (LET) offers electronic–optical hybridization at
the component level, which can continue Moore’s law to the quantum region without requiring a FET’s fabrication complexity, e.g., physical gate and doping, by employing optical gating and photoconductivity. Multiple independent gates
are therefore readily utilized to achieve unique functionalities without increasing chip space. LET device characteristics and
novel digital and analog applications, such as optical logic gates and optical amplification, are explored. Prototype cadmium selenide (CdSe) nanowire–based LETs show output and transfer characteristics resembling advanced FETs, e.g., on/off ratios up to ~1.0×106 with a source-drain voltage of ~1.43 V, gate-power of ~260 nW, and a subthreshold swing of
~0.3 nW/decade (excluding losses). The LET platform offers new electronic–optical integration strategies and high speed and low energy electronic and optical computing approaches.
This dissertation includes two additional aspects: (1) electron–phonon coupling at the nanoscale is both pertinent and important for electronic conductivity and energy efficiency in nanoscale devices including LETs; and (2) laser writing, or using a laser to perform post–growth modifications of specific optical and electrical characteristics for tangible device applications. Electron–phonon coupling is typically studied as an intrinsic property, which is particularly important for electronic transport properties at the nanoscale, but it is still shrouded in controversy at the nanoscale with contradictory experimental and theoretical findings. Resonant Raman spectroscopy leverages a nanostructure’s large surface–to–volume ratio to extrinsically perturb the electron–phonon coupling strength, which is obtained through the ratio of the first and second order Raman peaks, R = I2LO/I1LO (proportional to the Huang–Rhys factor). The laser–formation of tellurium–based species on ZnTe nanowires dynamically altered the (unitless) coupling strength from 7 to an impressive 32, which reduced to 5 after light surface ablation, while tuning the (532 nm) laser power from a few to 150. microwatts, while maintaining a constant exposure time, yielded a more modest dynamic range of 7 to 11. Other effects are also explored. Assuming the observed changes prove an intrinsic nanoscale effect, then the findings prompts revisiting of conventional theoretical frameworks and a reinterpretation of previous experimental findings for this and possibly other materials. Tunable coupling strengths also suggest the possibility of novel electronic and optoelectronic devices.
The ability to optically gate a LET and to externally tune electron–phonon coupling strengths strongly implies the ability to laser tune specific electronic and optical behaviors. Drastic modification of the electrical characteristics were observed, such as from converting an ohmic response (linear slope change) to rectified characteristics, and modification of both forward and reverse currents. Laser modification of nanostructures provides flexible circuit design using the same materials and device fabrication processes, which offers the potential for reduced manufacturing costs.