Effects of Dosage Increase on Electrical Properties of Metal-Oxide-Semiconductor Diodes with Mg-Ion-Implanted GaN Before Activation Annealing

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 x 10(11) and 1.5 x 10(12) 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 degrees 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.