Direct evidence of Be as an amphoteric dopant in GaN

Abstract

The interest in Be as an impurity in GaN stems from the challenge to understand why GaN can be doped $p$ type with Mg, while this does not work for Be. While theory has actually predicted an acceptor level for Be that is shallower than Mg, it was also argued that Be is not a suitable acceptor because its amphoteric nature, i.e., its tendency to occupy substitutional Ga as well as interstitial sites, would be considerably more pronounced than for Mg and hence lead to self-compensation. Using the emission channeling technique at the ISOLDE/CERN facility, we determined the lattice location of $^{11}\mathrm{Be}$ $({t}_{1/2}=13.8\phantom{\rule{0.16em}{0ex}}\mathrm{s})$ in different doping types of GaN as a function of implantation temperature. We find within an accuracy of 0.08 \AA{} that the location of interstitial Be is the one predicted by theory. The room temperature interstitial fraction of $^{11}\mathrm{Be}$ was correlated with the GaN doping type, being highest (up to \ensuremath{\sim}80%) in $p$ type and lowest in $n$-GaN, thus giving direct evidence for the amphoteric character of Be. We find that interstitial $^{11}\mathrm{Be}$ fractions are generally much higher than for Mg, which confirms that indeed self-compensation should be considerably more pronounced for Be. With rising implantation temperature, an increasing conversion of interstitial to substitutional Be is observed, involving at least two clearly identifiable steps at 50--150 \ifmmode^\circ\else\textdegree\fi{}C and 350--500 \ifmmode^\circ\else\textdegree\fi{}C. This suggests that the migration of interstitial Be may be subject to two different activation energies.