PROOF OF AMPHOTERIC Mg-DOPANT IN GaN

The emission channeling technique with short-lived isotopes (EC-SLI) gives direct information on the lattice location of radioactive isotopes implanted into single crystals. During 2016 radioactive 27Mg (t1/2=9.5 min) was implanted at CERN-ISOLDE into differently doped samples of the wide band-gap semiconductor GaN. Following implantations between room temperature and 800°C, the majority of 27Mg occupies the substitutional Ga sites, however, below 350 °C significant fractions were also found on interstitial positions ~0.6 Å away from ideal interstitial octahedral sites. The interstitial fraction of Mg was correlated with the GaN doping character, being highest (up to 31%) in samples p-type doped with 2x1019 cm^-3 stable Mg during growth, and lowest in Si-doped n-GaN, thus giving first-direct evidence for the amphoteric character of Mg. Implanting above 350 °C converts interstitial 27Mg to substitutional Ga sites, which allows estimating the activation energy for migration of interstitial Mg as between 1.3 and 2.0 eV.