Mg ions were implanted into Si-doped (5 × 1017 cm–3) n-GaN at a dose of 1.5 × 1011 or 1.5 × 1012 cm–2. MOS diodes were used to characterize the implanted GaN after 300 °C annealing for 3 h and after additional 500 °C annealing for 3 min. Although capacitance–voltage (C–V) characteristics varied with the dosage, the effects of acceptor-like defects induced by ion implantation were observed in the C–V characteristics independently of dosage and annealing temperature. A defect level at approximately 0.25 eV below the conduction band edge was detected electrically. By positron annihilation spectroscopy, its origin was identified as a divacancy consisting of Ga and N vacancies. It was found that its density compared with that of as-implanted GaN decreased with 300 °C annealing, and further increased with 500 °C annealing. This phenomenon was explained on the basis of the difference between the diffusion barriers of possible point defects.

The effect of increasing the dosage on the electrical properties of Mg‐ion‐implanted GaN before activation annealing is investigated to obtain knowledge on the defect levels generated by ion implantation. To probe the near‐surface region, GaN metal‐oxide‐semiconductor (MOS) structures with Al2O3 are used. Two kinds of MOS diodes with Mg‐ion dosages of 1.5 × 1011 and 1.5 × 1012 cm−2 implanted at 50 keV are prepared. Although anomalous capacitance–voltage (C–V) characteristics are observed for the low‐dosage sample, they are improved by annealing at 600 °C for 3 h. However, for the high‐dosage sample, more severe and persistent frequency dispersion is observed in the C–V characteristics, which is not improved by the same annealing. On the basis of the detailed analysis of capacitance–frequency (C–f) characteristics, it is concluded that the discrete interface trap at 0.2–0.3 eV below the conduction band is responsible for the frequency dispersion observed for the high‐dosage sample. Combined with the results of deep‐level transient spectroscopy, it is highly likely that the bulk deep levels affect the C–V and C–f characteristics. The possibility that the dominant deep levels are changed by the increase in Mg‐ion dosage is discussed.

The characteristics of a MOS diode with Mg-ion-implanted GaN before activation annealing were investigated. Mg ion implantation onto n-GaN with slightly high Si doping concentration (5×10 17 cm -3 ) was performed with a moderate dosage (1.5×10 12 cm -2 ). The completed MOS diode showed n-type features. The capacitance-voltage (C-V) and capacitance-frequency (C-f) characteristics of the MOS diode indicated that shallow surface Fermi level pinning and deep depletion occurred simultaneously. By applying the conductance method to the measured C-f characteristics, a discrete level at 0.2-0.3 eV below the conduction band edge was detected. On the basis of the simulation of the high-frequency-limit C-V curve, the detected discrete level distributed in the bulk of n-GaN rather than at the insulator/semiconductor interface, so that it caused surface Fermi level pinning at a relatively shallow energy level and deep depletion owing to its acceptorlike nature simultaneously.

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