Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Applied Physics Express  

Defect time-evolution was investigated in Mg ion-implanted GaN after annealing at 1573 K for an unprecedentedly long duration. Transmission electron microscopy directly revealed that annealing for over 30 min reduced defects inhibiting Mg activation, just like annealing at 1753 K for a short duration. The cathodoluminescence intensity of donor-acceptor pair originating from Mg acceptors increased as the duration increased, and the intensity after annealing for 60 min was higher than after short-duration annealing at 1753 K. These show the potential of lowering the annealing temperature by prolonging the duration, which would lead to practical annealing technology for Mg ion-implanted GaN.

DOI： 10.35848/1882-0786/abd308

Scopus

Publisher：Applied Physics Express  

By controlling a metal-oxide-semiconductor interface of an AlSiO/GaN system, the electron inversion channel mobility was significantly improved to 229 cm2 V−1 s−1 in a field-effect transistor. A 3 nm thick AlN interlayer formed by atomic layer deposition effectively suppressed the oxidation of the GaN surface and reduced the border traps, resulting in high channel mobility. An additional nitrogen radical treatment before AlN deposition further improved the subthreshold slope and the channel mobility, which was consistent with the lower charged defects extracted from the mobility analysis in the low effective normal field region.

DOI： 10.35848/1882-0786/ace33c

Web of Science

Scopus

Publisher：Physica Status Solidi - Rapid Research Letters  

Herein, transmission electron microscopy direct observations are used to examine the time evolution of dislocation loops in Mg-ion-implanted GaN during annealing in N2 atmospheres of 2.0 and 0.3 GPa. It is indicated in the results that the diffusion of the native defects, for both interstitials and vacancies, is retarded during annealing at the higher pressure. Furthermore, secondary ion mass spectrometry shows that annealing at the higher pressure retards the migration of Mg and increases Mg-acceptor concentration in the ion-implanted region. These findings provide a design principle of the postimplantation annealing process to activate ion-implanted Mg in GaN.

DOI： 10.1002/pssr.202300035

Web of Science

Scopus

Publisher：Journal of Applied Physics  

We carried out atomic-scale observations of Mg-ion-implanted GaN by transmission electron microscopy (TEM) and atom probe tomography (APT) to clarify the crystallographic structures of extended defects and Mg agglomerations that form during post-implantation annealing. The complementary TEM and APT analyses have shown that Mg atoms agglomerate at dislocations that bound extended defects. The concentration of Mg is higher at the dislocations with a larger Burgers vector. This indicates that Mg agglomeration is caused by the pressure at the dislocations. Mg concentration in highly Mg-rich regions is 1 at. %, which exceeds the solubility limit of Mg in GaN. We investigated isothermal and isochronal evolution of the defects by TEM, cathodoluminescence analysis, and positron annihilation spectroscopy. The results indicated that the intensity of donor-acceptor pair emission increases with the annealing temperature and duration and reaches a maximum after elimination of the extended defects with highly Mg-rich regions. These results strongly suggest that such extended defects reduce the acceptor formation and that they as well as the previously reported compensating centers, such as N-related vacancies, can inhibit the formation of p-type GaN. The mechanism by which the extended defects reduce acceptor formation is discussed.

DOI： 10.1063/5.0097866

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Journal of Applied Physics  

Sputtering enables uniform and clean deposition over a large area, which is an issue with exfoliation and chemical vapor deposition methods. On the other hand, the process of physical vapor deposition (PVD) film formation has not yet been clarified. We prepared several samples from the sub-monolayer region, and performed Raman spectroscopy, X-ray photon spectroscopy and high-angle annular dark-field scanning transmission electron microscopy. From these results, the internal stresses inherent to PVD films, the bonding states specific to sub-monolayers, and the unique film structure and the grain formation process of PVD films were discussed from the perspective of sub-monolayers. As a conclusion, we found that it is important to suppress the formation of sub-monolayers on the substrate to completely form the first layer.

DOI： 10.35848/1347-4065/ac3fc9

Web of Science

Scopus

Event date： 2023.11

Language：English   Presentation type：Oral presentation (general)  

Event date： 2023.9

Language：English   Presentation type：Oral presentation (general)  

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：上智大学四谷キャンパス   Country：Japan