Effects of radiation damage on GaN epitaxial layer arising from argon ion implantation for edge termination

To suppress the electric -field crowding at the edge of GaN-based power devices and enhance the breakdown voltage as well, argon ion (Ar+) implantation has been demonstrated an efficient process of edge termination for n -type GaN, that is realized by the introduction of radiation -induced defects to modify electric -field distribution around the edge of devices. However, a high fluence of Ar+ irradiation inevitably causes radiation damage, which is absolutely detrimental to the electrical and material properties of GaN crystal. Therefore, the purpose of this study is to investigate the effects of radiation damage arising from Ar+ implantation on n -type GaN epitaxial layer. 180 keV Ar ions with various fluences ranging from 4.8 x 1013 to 6 x 1015 cm -2 were implanted, forming a thin damaged area near the surface of GaN epitaxial layer. The characteristics of Ar+-implanted GaN epitaxial layer were then thoroughly investigated by Hall effect measurement, X-ray diffraction (XRD), photoluminescence (PL), and Raman scattering spectroscopy. The results indicated that the electron concentration of GaN decreases with the increase of Ar+ fluence. About 32.5 % of carriers in GaN are removed after Ar+ irradiation to a maximum fluence of 6 x 1015 cm -2. As revealed by PL spectra, Ar+ implantation -induced defects would trap free carriers and behave like non -radiative recombination centers. An abrupt increase in lattice strain derived from XRD spectra implies a localized amorphous layer that may be formed in GaN crystal when Ar+ fluence is higher than 1.2 x 1015 cm -2. The Raman spectra also evidenced that Ar+ implantation into GaN leads to N sublattice damage and degradation in electrical conduction properties. The results obtained in this study are expected to be useful for the design of Ar+-implanted edge termination for GaN power devices.