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Defense Date
2007
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Electrical Engineering
First Advisor
Dr. Hadis Morkoc
Abstract
In this dissertation, GaN growth on porous templates by metalorganic chemical vapor deposition (MOCVD) was studied. The motivation of this research is pursuing an effective reduction of defects in GaN by its submicron-scale and nano-scale epitaxial lateral overgrowth (ELO) on these porous templates, which included porous TiN/GaN (P-TiN), imprint lithography patterned Ti/GaN (IL-Ti), carbon-face nano-porous SiC (C-PSC), and silicon-face nano-porous SiC (Si-PSC). The porous TiN/GaN was formed in situ in MOCVD reactor by annealing a Ti-covered GaN seed layer. This simplicity makes the GaN ELO on the P-TiN more cost-efficient than the conventional ELO which requires ex situ photolithography and/or etching. Both the GaN nano-ELO and the GaN micron-ELO could be realized on P-TiN by controlling the GaN nucleation scheme. The reduction efficacy of edge threading dislocation (TD) was ~15 times. The optical characterization indicated that the non-radiative point-defects in GaN grown were reduced significantly on the P-TiN.The imprint lithography patterned Ti/GaN had uniformly distributed submicron Ti pads on GaN seed layer. These Ti pads acted as GaN ELO masks. The TD reduction efficacy of the IL-Ti was only ~2 due to the low coverage of Ti (~25%) on the GaN seed layer and the low pressure (30 Torr) employed during GaN ELO. Even with a small reduction of TDs, the point-defects in GaN were effectively lowered by the IL-Ti. Hydrogen polishing, sacrificial oxidation, and chemical mechanical polishing were employed to remove surface damage on the PSC substrates. Nitrogen-polarity GaN grown on the C-PSC was highly dislocated because the rough surface of C-PSC induced strong misorientation between GaN nucleation islands. The efficacy of Si-PSC on defect reduction primarily depended on the GaN nucleation schemes. A high density of GaN nano-nucleation-islands was required to realize the GaN nano-ELO extensively. With such a nucleation scheme, the GaN grown on Si-PSC had a ~20 times reduction on the density of the mixed and screw TDs compared with control sample. This growth method is promising for effective defect reduction within a small GaN thickness. Reducing the GaN nucleation density further lowered the TD density but also diminished the efficacy of Si-PSC. These results were explained by a growth model based on the mosaic structure of GaN.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
June 2008
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Comments
Part of Retrospective ETD Collection, restricted to VCU only.