ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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Description
Gallium Nitride (GaN), being a wide-bandgap semiconductor, shows its advantage over the conventional semiconductors like Silicon and Gallium Arsenide for high temperature applications, especially in the temperature range from 300°C to 600°C. Development of stable ohmic contacts to GaN with low contact resistivity has been identified as a prerequisite to the success of GaN high temperature electronics. The focus of this work was primarily derived from the requirement of an appropriate metal contacts to work with GaN-based hybrid solar cell operating at high temperature.
Alloyed Ti/Al/Ni/Au contact and non-alloyed Al/Au contact were developed to form low-resistivity contacts to n-GaN and their stability at high temperature were studied. The alloyed Ti/Al/Ni/Au contact offered a specific contact resistivity (ρc) of 6×10-6 Ω·cm2 at room temperature measured the same as the temperature increased to 400°C. No significant change in ρc was observed after the contacts being subjected to 400°C, 450°C, 500°C, 550°C, and 600°C, respectively, for at least 4 hours in air. Since several device technology prefer non-alloyed contacts Al/Au metal stack was applied to form the contacts to n-type GaN. An initial ρc of 3×10-4 Ω·cm2, measured after deposition, was observed to continuously reduce under thermal stress at 400°C, 450°C, 500°C, 550°C, and 600°C, respectively, finally stabilizing at 5×10-6 Ω·cm2. Both the alloyed and non-alloyed metal contacts showed exceptional capability of stable operation at temperature as high as 600°C in air with low resistivity ~10-6 Ω·cm2, with ρc lowering for the non-alloyed contacts with high temperatures.
The p-GaN contacts showed remarkably superior ohmic behavior at elevated temperatures. Both ρc and sheet resistance (Rsh) of p-GaN decreased by a factor of 10 as the ambient temperature increased from room temperature to 390°C. The annealed Ni/Au contact showed ρc of 2×10-3 Ω·cm2 at room temperature, reduced to 1.6×10-4 Ω·cm2 at 390°C. No degradation was observed after the contacts being subjected to 450°C in air for 48 hours. Indium Tin Oxide (ITO) contacts, which has been widely used as current spreading layer in GaN-base optoelectronic devices, measured an initial ρc [the resistivity of the ITO/p-GaN interface, since the metal/ITO ρc is negligible] of 1×10-2 Ω·cm2 at room temperature. No degradation was observed after the contact being subjected to 450°C in air for 8 hours.
Accelerated life testing (ALT) was performed to further evaluate the contacts stability at high temperatures quantitatively. The ALT results showed that the annealed Ni/Au to p-GaN contacts is more stable in nitrogen ambient, with a lifetime of 2,628 hours at 450°C which is approximately 12 times longer than that at 450°C in air.
Alloyed Ti/Al/Ni/Au contact and non-alloyed Al/Au contact were developed to form low-resistivity contacts to n-GaN and their stability at high temperature were studied. The alloyed Ti/Al/Ni/Au contact offered a specific contact resistivity (ρc) of 6×10-6 Ω·cm2 at room temperature measured the same as the temperature increased to 400°C. No significant change in ρc was observed after the contacts being subjected to 400°C, 450°C, 500°C, 550°C, and 600°C, respectively, for at least 4 hours in air. Since several device technology prefer non-alloyed contacts Al/Au metal stack was applied to form the contacts to n-type GaN. An initial ρc of 3×10-4 Ω·cm2, measured after deposition, was observed to continuously reduce under thermal stress at 400°C, 450°C, 500°C, 550°C, and 600°C, respectively, finally stabilizing at 5×10-6 Ω·cm2. Both the alloyed and non-alloyed metal contacts showed exceptional capability of stable operation at temperature as high as 600°C in air with low resistivity ~10-6 Ω·cm2, with ρc lowering for the non-alloyed contacts with high temperatures.
The p-GaN contacts showed remarkably superior ohmic behavior at elevated temperatures. Both ρc and sheet resistance (Rsh) of p-GaN decreased by a factor of 10 as the ambient temperature increased from room temperature to 390°C. The annealed Ni/Au contact showed ρc of 2×10-3 Ω·cm2 at room temperature, reduced to 1.6×10-4 Ω·cm2 at 390°C. No degradation was observed after the contacts being subjected to 450°C in air for 48 hours. Indium Tin Oxide (ITO) contacts, which has been widely used as current spreading layer in GaN-base optoelectronic devices, measured an initial ρc [the resistivity of the ITO/p-GaN interface, since the metal/ITO ρc is negligible] of 1×10-2 Ω·cm2 at room temperature. No degradation was observed after the contact being subjected to 450°C in air for 8 hours.
Accelerated life testing (ALT) was performed to further evaluate the contacts stability at high temperatures quantitatively. The ALT results showed that the annealed Ni/Au to p-GaN contacts is more stable in nitrogen ambient, with a lifetime of 2,628 hours at 450°C which is approximately 12 times longer than that at 450°C in air.
ContributorsZhao, Shirong (Author) / Chowdhury, Srabanti (Thesis advisor) / Goodnick, Stephen (Committee member) / Zhao, Yuji (Committee member) / Nemanich, Robert (Committee member) / Arizona State University (Publisher)
Created2016
Description
This dissertation aims to study and understand the effect of nonlinear dynamics and quantum chaos in graphene, optomechanics, photonics and spintronics systems.
First, in graphene quantum dot systems, conductance fluctuations are investigated from the respects of Fano resonances and quantum chaos. The conventional semi-classical theory of quantum chaotic scattering used in this field depends on an invariant classical phase-space structure. I show that for systems without an invariant classical phase-space structure, the quantum pointer states can still be used to explain the conductance fluctuations. Another finding is that the chaotic geometry is demonstrated to have similar effects as the disorders in transportations.
Second, in optomechanics systems, I find rich nonlinear dynamics. Using the semi-classical Langevin equations, I demonstrate a quasi-periodic motion is favorable for the quantum entanglement between the optical mode and mechanical mode. Then I use the quantum trajectory theory to provide a new resolution for the breakdown of the classical-quantum correspondences in the chaotic regions.
Third, I investigate the analogs of the electrical band structures and effects in the non-electrical systems. In the photonic systems, I use an array of waveguides to simulate the transport of the massive relativistic particle in a non-Hermitian scenario. A new form of Zitterbewegung is discovered as well as its analytical explanation. In mechanical systems, I use springs and mass points systems to achieve a three band degenerate band structure with a new pair of spatially separated edge states in the Dice lattice. A new semi-metal phase with the intrinsic valley-Hall effect is found.
At last, I investigate the nonlinear dynamics in the spintronics systems, in which the topological insulator couples with a magnetization. Rich nonlinear dynamics are discovered in this systems, especially the multi-stability states.
First, in graphene quantum dot systems, conductance fluctuations are investigated from the respects of Fano resonances and quantum chaos. The conventional semi-classical theory of quantum chaotic scattering used in this field depends on an invariant classical phase-space structure. I show that for systems without an invariant classical phase-space structure, the quantum pointer states can still be used to explain the conductance fluctuations. Another finding is that the chaotic geometry is demonstrated to have similar effects as the disorders in transportations.
Second, in optomechanics systems, I find rich nonlinear dynamics. Using the semi-classical Langevin equations, I demonstrate a quasi-periodic motion is favorable for the quantum entanglement between the optical mode and mechanical mode. Then I use the quantum trajectory theory to provide a new resolution for the breakdown of the classical-quantum correspondences in the chaotic regions.
Third, I investigate the analogs of the electrical band structures and effects in the non-electrical systems. In the photonic systems, I use an array of waveguides to simulate the transport of the massive relativistic particle in a non-Hermitian scenario. A new form of Zitterbewegung is discovered as well as its analytical explanation. In mechanical systems, I use springs and mass points systems to achieve a three band degenerate band structure with a new pair of spatially separated edge states in the Dice lattice. A new semi-metal phase with the intrinsic valley-Hall effect is found.
At last, I investigate the nonlinear dynamics in the spintronics systems, in which the topological insulator couples with a magnetization. Rich nonlinear dynamics are discovered in this systems, especially the multi-stability states.
ContributorsWang, Guanglei (Author) / Lai, Ying-Cheng (Thesis advisor) / Vasileska, Dragica (Committee member) / Ning, Cun-Zheng (Committee member) / Zhao, Yuji (Committee member) / Arizona State University (Publisher)
Created2017