Encapsulant-Dependent Effects of Long-Term Low-Temperature Annealing on Interstitial Defects in Mg-Ion-Implanted GaN

The encapsulant-dependent effects of long-term low-temperature annealing on defects in Mg-ion-implanted GaN were investigated using metal-oxide-semiconductor (MOS) diodes. Annealing was carried out at 600 degrees C under nitrogen flow without or with a cap layer of Al2O3, SiO2, or SiN. For annealing at 600 degrees C for 3 h, the capacitance-voltage characteristics of the Al2O3 cap annealed samples indicated the existence of acceptor-like defects, whereas those of the capless, SiO2 cap and SiN cap annealed samples exhibited bumps, which indicated the existence of a donor-like defect level at around 0.8 eV from the conduction band edge E-C. A more distinct result was obtained for annealing at 600 degrees C for 30 h. Namely, annealing of samples with the Al2O3 cap layer induced an acceptor-like defect level at E-C-0.9 eV, whereas that with the SiN cap layer induced a donor-like defect level at E-C-0.8 eV. Secondary ion mass spectroscopy and transmission electron microscopy studies revealed that interstitial Ga (Ga-i) in Mg-implanted GaN diffused into the Al2O3 cap layer but not into the SiN cap layer after annealing. Most likely, the detected E-C-0.8 eV level can be assigned to interstitial Ga-i

Low-temperature annealing behavior of defects in Mg-ion-implanted GaN studied using MOS diodes and monoenergetic positron beam

Mg ions were implanted into Si-doped (5 x 10(17) cm(-3)) n-GaN at a dose of 1.5 x 10(11) or 1.5 x 10(12) cm(-2). MOS diodes were used to characterize the implanted GaN after 300 degrees C annealing for 3 h and after additional 500 degrees 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 degrees C annealing, and further increased with 500 degrees C annealing. This phenomenon was explained on the basis of the difference between the diffusion barriers of possible point defects

Effects of a photo-assisted electrochemical etching process removing dry-etching damage in GaN

We investigated the ability of a photo-assisted electrochemical (PEC) etching process to remove the damage that dry etching causes in the near-surface region of GaN samples. The process consists of anodic oxidation of the GaN surface and subsequent dissolution of the oxide with a chemical treatment, and the extent of the PEC reactions depends on the total charge density transferred in them. The PEC process was conducted for samples prepared with various dry-etching conditions followed by fabrication of Schottky barrier diodes (SBDs) and metal-insulatorsemiconductor (MIS) capacitors. The PEC process greatly improved the barrier height, ideality factor, and reverse leakage current of SBDs. Capacitance-voltage measurements of MIS capacitors revealed that the densities of interface states and discrete traps were both reduced by the PEC process. The results obtained here show that the PEC process can remove dry-etching damage from the GaN surface. (C) 2018 The Japan Society of Applied Physic

X-ray photoelectron spectroscopy study on effects of ultra-high-pressure annealing on surface of Mg-ion-implanted GaN

The effects of ultra-high-pressure annealing (UHPA) on the surface of Mg-ion-implanted GaN were investigated by X-ray photoelectron spectroscopy (XPS). After Mg ion implantation or Mg-N co-implantation, GaN was annealed at 1400 degrees C for 5 min under a nitrogen pressure of 1 GPa. No deterioration of the surface stoichiometry occurred after UHPA despite the extremely high annealing temperature. The angle-resolved XPS with calibration showed that the surface Fermi level was pinned at 0.5 eV from the conduction band edge after dehydrogenation subsequent to UHPA. However, the absence of pinning at the charge neutrality level showed that surface disorder was absent after UHPA. The surface photovoltaic effect as evidence of the achievement of p-type conduction even in the near-surface region was more remarkable for Mg-N-ion-implanted samples after dehydrogenation subsequent to UHPA. There is the possibility that the density of N-vacancy-related defects was reduced more by Mg-N co-implantation

Detection of defect levels in vicinity of Al₂O₃/p-type GaN interface using sub-bandgap-light-assisted capacitance-voltage method

Defect levels in the vicinity of the Al2O3/p-type GaN interface were characterized using a sub-bandgap-light-assisted capacitance-voltage (C-V) method. For metal-oxide-semiconductor (MOS) diodes prepared using p-type GaN (p-GaN) and Al2O3 formed by atomic layer deposition, the C-V curves measured in the dark showed capacitance saturation at a negative bias and a large negative voltage shift compared with ideal curves, which implied the effects of donor-like gap states in the vicinity of the Al2O3/p-GaN interface. Upon illumination with monochromated sub-bandgap light with photon energies higher than 2.0 eV under a large positive bias, the subsequently measured C-V curves showed three plateaus. The plateau under the positive bias voltage due to the surface inversion appeared despite the sub-bandgap illumination, which did not appear at 1.8 eV light illumination, indicating the existence of midgap defect levels. Moreover, the other plateaus were attributed to defect levels at 0.60 and 0.7-0.8 eV above the valence band maximum. For a sample whose surface was prepared by photo-electrochemical (PEC) etching to a depth of 16.5 nm, the C-V curve measured in the dark showed a reduced voltage shift compared with the unetched sample. Furthermore, sub-bandgap-light-assisted C-V curves of the sample with PEC etching showed no plateau at a positive bias, which indicated the reduction in the density of the midgap defect states. Possible origins of the detected defect levels are discussed. The obtained results showed that the interface control can improve the properties of p-GaN MOS structures. Published under an exclusive license by AIP Publishing