A study of carbon and iron charged point defects in gallium nitride: electronic structure implications for high-power photoconductive solid state switch applications
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There is growing demand for high-performance electronics in high volt- age, high current, and high frequency efficiency requirements that current materials (e.g., Si) are not fulfilling. Within the last few years, the rate of development of Si power electron- ics has slowed as the MOSFET silicon power asymptotically approached its theoretical limits. Gallium natride (GaN) grown on top of a silicon substrate could displace silicon across a significant portion of the power management market. Doping elements in bulk GaN may influence and enhance its prop- erties. Carbon doping of GaN is potentially efficient and useful material for photo-conductive solid-state switches (PCSSs), also called photo-conductive semiconductor switches. However, to make effective use of the rich capa- bilities of device-scale engineering design tools (e.g., Technology Computer- Aided Design (TCAD)) it is necessary to know a variety of material de- pendent parameters for which experimental results have not been obtained. Therefore, the ability to determine those parameters via ab initio calcula- tions is essential, especially when the material contains some type of defect or dopant. To overcomes this dilemma, we proposed a simulation methodology to ex- tract the needed parameters form atomistic ab initio calculation of bulk (un- doped) GaN, carbon-doped GaN, and iron-doped GaN. The proposed method chain was successfully produced the required parameters including electronic structure, polarization properties, phonon calculation, and mechanical and spectroscopic properties for GaN, C-doped GaN, and Fe-GaN crystals. The parameter values were subsequently used in a TCAD tool to compute trans- port properties and breakdown voltage of GaN, C-doped GaN, and Fe-GaN. Result shows that all material properties such as mechanical, optical, polar- ization, transport properties, and the breakdown transport properties and breakdown voltage changed due to the presence of dopants. The comparison of breakdown voltage models for C-doped and Fe-doped GaN channel layers revealed that Fe-doped GaN has a greater breakdown voltage. To produce a more accurate simulation of GaN HEMT, it is necessary to take into account the parameters of a genuine model with their actual values rather than rely- ing on a generic dopant. Key Words: PCSS, GaN, C-doped GaN, Fe-doped GaN, point defect, electronic structure, polarization properties, Piezoelectric constant, phonon calculation, mechanical and optical properties, transport properties, XANES/ELNES spectrscopy, device Simulation (TCAD), Multiscal Methods, OLCAO, break- down voltage, electron velocity, mobility, scattering rate.
Table of Contents
Introduction -- Background -- Computational methods -- Results -- Conclusion and future work
Ph.D. (Doctor of Philosophy)