Diffusion in a magnesium (Mg)-implanted homoepitaxial GaN layer during ultra-high-pressure annealing (UHPA, in ambient nitrogen, under 1 GPa) was investigated. Annealing at 1573 K resulted in Mg-segregation at the edge of the implanted region, which was suppressed using a higher temperature of 1673 K. Hydrogen (H) atoms were incorporated during the UHPA, resulting in the Mg and H developing the same diffusion profile in the deeper region. The diffusion coefficient of the Mg-implanted sample was 3.3 × 10 −12 cm 2 s −1 at 1673 K from the annealing duration dependence, 30 times larger than that of the epitaxial Mg-doped sample, originating from ion implantation-induced defects.

Plasma-induced damage was reduced by multistep-bias etching that involved a stepwise decrease of the etching bias power (Pbias) and subsequent annealing. The depth of damage at Pbias = 60 W was determined to be 60 nm from the capacitance–voltage characteristics of Ni/Al2O3/etched-GaN metal-oxide-semiconductor diodes. The damaged layer was removed by subsequent etching at Pbias = 5 W and 2.5 W. The residual and shallow damage induced by the low Pbias was then recovered by subsequent annealing at 400 °C. The multistep-bias etching of inductively coupled plasma reactive ion etching was thus confirmed to be effective for achieving a high etching rate with low damage.

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.

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Herein, we report on a photoluminescence (PL) method for evaluating the Mg acceptor concentration in GaN, which has thus far been difficult and costly to determine using conventional electrical methods. The proposed method is based on the intensity ratio between the acceptor bound exciton emission and free exciton emission in the PL spectra of GaN. The calibration curve for the Mg acceptor concentration ranging from 6.4 × 1016 to 1.2 × 1018 cm−3 was obtained from the concentration dependence of the PL spectra recorded at 40 K. Furthermore, the detection limit of the Mg acceptor concentration from this method was estimated to be approximately 1010 cm−3. Results indicate that our method enables the unambiguous, simple, low-cost, and nondestructive quantification of the Mg acceptor concentration of p-type GaN, which is important in power device applications.