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Electron paramagnetic resonance (EPR) spectroscopy was used to study the point defects in 2 × 1017–1019 cm−3 C-doped GaN substrates grown by hydride vapor phase epitaxy. The intensity of an isotropic signal with g = 1.987 ± 0.001 increased monotonically with the carbon concentration, indicating that the EPR signal represents a carbon-related defect. In each sample, the signal intensity increased under illumination with photon energy greater than 2.75 eV, and the photo-induced signal decreased with subsequent illumination at 0.95 eV. A second signal, well-documented to be a shallow donor, appeared along with the g = 1.987 signal in the most lightly doped samples. The appearance of the donor confirms that the photo-induced increase is caused by excitation of an electron to the conduction band and implies that a defect level for the carbon-related center is about 1 eV above the valence band edge, consistent with temperature-dependent Hall measurements.

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate a type of point defect present in 1019 cm−3 carbon-doped GaN substrates grown by hydride vapor phase epitaxy. A broad, isotropic resonance at g ∼ 1.987 was observed at 3.5 K, and the EPR intensity increased with illumination at energies greater than 2.75 eV and decreased with photon energies greater than 0.95 eV. The latter is consistent with a deep level of 0.95 eV above the valence band maximum and implies that the associated defect likely participates in donor compensation. The ionization energy for this defect is close to the predicted value for the (−/0) transition level of CN and transition levels associated with Ga vacancies such as VGa and VGa-ON-2H.

Herein, a carbon‐related point defect in thick free‐standing carbon‐doped GaN substrates grown by halide chemical vapor deposition is examined. Carbon is intentionally introduced to concentrations between 2 × 1017 and 1019 cm−3, and the number of point defects is proportional to the carbon concentration. The carbon center is detected using electron paramagnetic resonance spectroscopy after photo‐excitation with light greater than 2.8 eV. Simultaneous monitoring of the defect and a shallow donor confirms that the excitation occurs via removal of an electron from the deep carbon‐related acceptor and subsequent capture by the shallow donor. The study indicates that the defect level for the carbon defect is at least 0.7 eV above the valence band edge and therefore an excellent candidate for growth of semi‐insulating GaN.