Mg-implanted p-type Gallium Nitride (GaN)
Atom probe tomography (APT) analysis is now being applied not only to metals but also to semiconductors and insulators. Here, an example of APT analysis for gallium nitride (GaN) is presented. GaN is expected to be a next-generation power semiconductor, and selective formation of p-type/n-type regions is essential for practical applications. Ion implantation is regarded as a promising method, but Mg ion implantation for p-type formation inevitably introduces defects such as dislocations and vacancies. STEM-EDS studies have also reported that, during the annealing process for repairing these defects and activating Mg, Mg can segregate at defects. However, the concentration of implanted Mg is extremely low (about 0.01 at% or less), so many aspects of the three-dimensional distribution of Mg dopants remain unclear. In this example, an APT specimen of GaN implanted with 1×1019 cm－3 (about 0.01 at%) Mg ions, and annealed at 1300°C, is shown together with a corresponding low-angle annular dark-field STEM (LAADF-STEM) image. Under these STEM observation conditions, defects such as those caused by lattice strain appear with bright contrast. The resulting three-dimensional Mg map enables detailed understanding of the spatial distribution of Mg atoms within the same field of view. As a result, in addition to Mg segregation at dislocation loops, the formation of high-density Mg clusters was clearly observed, and it was shown that these clusters are a factor inhibiting the p-type activation of Mg. Furthermore, process improvements based on such knowledge from nanoscale structure analysis have been developed, and it has also been reported that activation annealing under ultra-high pressure exceeding 1 GPa allows both the recovery of crystallinity and efficient p-type activation.
- J. Uzuhashi, J. Chen, A. Kumar, W. Yi, T. Ohkubo, R. Tanaka, S. Takashima, M. Edo, K. Sierakowski, M. Bockowski, H. Sakurai, T. Kachi, T. Sekiguchi, and K. Hono, "Atomic-scale investigation of implanted Mg in GaN through ultra-high-pressure annealing", J. Appl. Phys. 131, 185701 (2022)
- T.T. Sasaki, H. Sepehri-Amin, J. Uzuhashi, T. Ohkubo, and K. Hono, "Complementary and correlative (S)TEM/APT analysis of functional and structural alloys", MRS Bull. 47, 688–695 (2022)
- A. Kumar, J. Uzuhashi, T. Ohkubo, R. Tanaka, S. Takashima, M. Edo, and K. Hono, "Atomic-scale quantitative analysis of implanted Mg in annealed GaN layers on free-standing GaN substrates", J. Appl. Phys. 126, 235704 (2019)