All ETDs from UAB

Advisory Committee Chair

Mary E Zvanut

Advisory Committee Members

Kannatassen Appavoo

Renato P Camata

Tracy P Hamilton

Patrick Kung

Sergey B Mirov

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences


GaN is being investigated as an active material in light-emitting diodes and high electron mobility transistors. Recently, it has attracted researchers’ attention for high-power applications due to its larger bandgap and electric breakdown field compared to other well‐known semiconductors such as Si, GaAs, and SiC. High-power applications in electronic devices often require semi-insulating layers or substrates for homoepitaxial growth. However, as-grown GaN is n-type due to the presence of unintentional donors. The acceptor impurities like carbon must be added to create semi-insulating material. Although it is established that incorporating carbon impurity makes semi-insulating GaN, the defect responsible and the process involved are still controversial. This work provides insight into the defect responsible for the semi-insulating nature of GaN:C. An investigation was carried out by electron paramagnetic resonance (EPR) spectroscopy on 2x1017 to 1x1019 cm-3 C-doped GaN substrates grown by hydride vapor phase epitaxy. A small resonance representing ~1017 cm-3 defects with a nearly isotropic g ~ 1.987 ± 0.001 is obtained in all as-received samples. The defect density in the different samples increases monotonically with carbon content, indicating the defect is carbon-related. The intensity of g ~ 1.987 resonance can be enhanced and quenched after light illumination. The time evolution of the defect density is measured and fit to get a cross-section spectrum. The cross-sections were analyzed using an expression for absorption by defects with strong electron-phonon coupling. The threshold for photoexcitation and iv photo-quenching was 2.50 eV and 0.70 eV, respectively, with a symmetric lattice relaxation energy of 0.25 eV, which agrees with the predicted value for CN. The other resonance, which appears only after 2.75 eV or above illumination in the lightly doped samples with g// =1.951 and g⊥=1.948, is the well documented, shallow donor. We observed the direct charge transfer between CN and the donor, suggesting that the CN acceptor can compensate the donor and create semi-insulating material. This work identifies defects, CN and shallow donor, in semi-insulating GaN:C and discusses the charge transfer mechanism between the defects. The characterization technique was non-destructive and can provide important information about various insulating and semi-insulating materials.