Hydrogen isotope exchange and the surface barrier in p-type gallium nitride

Fourier-transform infrared spectroscopy was used to examine the replacement of one H isotope by another within p-type, Mg-doped GaN during heating in H2 gas at 700 °C. A central objective was further mechanistic understanding of the surface-barrier effect that has previously been shown to limit H release during postgrowth thermal activation of H-passivated Mg acceptors. Ambient H21 or H22 was found to accelerate the removal of the other isotope by orders of magnitude, consistent with recombinative desorption of H2 being rate limiting. The results agree closely with a predictive model describing the interrelated behaviors of H within the semiconductor and on the surface. The saturation concentration of H decreased during the heat treatments, presumably indicating a reduction in the effective level of p-type doping, which is provisionally ascribed to compensation by N vacancies.