Electrical activity of Mg clustering at nanoscale defects induced by N ion implantation in GaN

Abstract

The p-type doping of GaN using Mg ion implantation remains a critical challenge in the development of GaN power devices. Herein, we demonstrate that Mg clustering, induced by sequential N ion implantation, impacts the acceptor concentration (Na), compensating donor concentration (Nd), and acceptor activation energy (ΔEa). N was implanted at the same concentration as Mg to suppress Mg diffusion. Hall-effect measurements indicated that, for Mg doses above 1 × 1019 cm−3, Na reached a plateau, whereas Nd continued to increase. Consequently, the net acceptor concentration (Na − Nd) reached a maximum of 4 × 1018 cm−3 at a Mg dose of 1 × 1019 cm−3. ΔEa decreased with increasing Mg dose. Atomic-resolution structural analyses revealed that nanoscale defects generated by N implantation induced Mg clustering around these defects, with the cluster density increasing with Mg dose. Notably, peak Mg concentrations within these clusters exceeded 1 × 1021 cm−3 and increased with Mg dose, whereas Mg atoms outside these clusters remained uniformly dispersed in the range of 1.3–1.5 × 1018 cm−3 regardless of Mg dose. These findings suggest that the increase in Na up to a Mg dose of 1 × 1019 cm−3 can be attributed to the Mg atoms within these Mg-rich clusters acting as acceptors, which also lowered ΔEa. Conversely, Mg atoms at or near the peak Mg-concentration sites likely acted as compensating donors, contributing to the increase in Nd with increasing Mg dose. These findings elucidate the impact of Mg clustering induced by nanoscale implantation defects on the p-type conductivity of GaN, providing insight for improving ion-implantation doping strategies in GaN.