Dissertation Defense Schedule
Academic Excellence
Sharing original dissertation research is a principle to which the University of Delaware is deeply committed. It is the single most important assignment our graduate students undertake and upon completion is met with great pride.
We invite you to celebrate this milestone by attending their dissertation defense. Please review the upcoming dissertation defense schedule below and join us!
PROGRAM | Materials Science & Engineering
Electronic and thermal properties of wide bandgap materials from density functional theory
By: Tianshi Wang Chair: Chaoying Ni
ABSTRACT
Wide bandgap materials, e.g. SiC, GaN, ZnO, Ga2O3, and diamond, find many applications in microelectronics such as high electron mobility transistors (HEMT), field effect transistors, and light-emitting diodes (LED). Great efforts are being made on the wide bandgap materials as mandated by next generation device design and fabrications. This work focuses on three topics: heat transport in SiC/Diamond/Si systems, the electronic properties of (AlxGa1-x)2O3 alloys, and phonon-limited electron transport in ZnO and GaN.
The computational simulation is based upon the density functional theory (DFT) which provides efficient means to investigate a system from a quantum mechanics description and has become a powerful tool in computational materials science. This work uses a combined approach of DFT, density functional perturbation theory (DFPT), classical heat diffusion models, and special quasirandom structures (SQS) models.
We first found that, in polycrystalline diamond, the effective thermal conductivity increases with respect to a grain size below 300 nm and it then levels off above 300 nm. We also derived thermal barrier resistances in the SiC/Si, diamond/Si, and diamond/SiC heterostructures which are important parameters in developing related composites and simulating device performances. Second, for (AlxGa1-x)2O3 alloys, the most of its band offset was found to arise from the discontinuity in the conduction band. Our results explain well the experimental data in literature and the consequential advantages for designing modulation-doped field effect transistors (MODFETs) based on (AlxGa1-x)2O3/Ga2O3. We further predicted a thermodynamically stable compound AlGaO3 with Al occupying the octahedral sites and Ga occupying the tetrahedral sites. Finally, we found that the much lower electron mobility in ZnO compared to GaN is from the stronger electron-phonon (e-ph) scattering in ZnO, which is dominated by piezoelectric and polar-optical-phonon (POP) interactions. This characteristic phonon-limited electron transport behavior revealed in this investigation also gives insights applicable to many other materials
The Process
Step-by-Step
Visit our “Step-by-Step Graduation Guide” to take you through the graduation process.From formatting your Dissertation to Doctoral Hooding procedures.
Dissertation Manual
Wondering how to set up the format for your paper. Refer to the “UD Thesis/Dissertation Manual” for formatting requirements and more.
Defense Submission Form
This form must be completed two weeks in advance of a dissertation defense to meet the University of Delaware Graduate and Professional Education’s requirements.
