Isotope effects on the rate of electron-beam dissociation of Mg–H complexes in GaN

The effect of low-energy electron-beam irradiation on the stability of acceptor–hydrogen complexes in Mg-doped GaN has been directly examined with infrared optical spectroscopy. Consistent with prior electrical transport data, we find that Mg–H pairs begin to break apart under 25 keV electron-beam exposure at doses of a few mC/cm2. However, we find that, even after long exposures, roughly 12 of the acceptor–hydrogen pairs remain unaffected by the electron exposure. Using Mg-doped samples that have been vacuum annealed and D2 gas exposed, we demonstrate that there is a large (∼×5) isotopic shift in the beam-induced debonding rate of these acceptor–hydrogen complexes. H and D remain in the material during these treatments, and Mg–H or Mg–D reforms during postirradiation annealing. The implications of these observations for understanding the nature of the debonding process and the subsequent reactions of the detached H/D in the GaN lattice are discussed.