Amphoteric arsenic in GaN

We have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive $^{73}$As. We give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fact that As$\scriptstyle_{Ga}\,$ " anti-sites ” are not minority defects provide additional aspects to be taken into account for an explanantion of the so-called “ miscibility gap ” in ternary GaAs$\scriptstyle_{1-x}$N$\scriptstyle_{x}$ compounds, which cannot be grown with a single phase for values of $x$ in the range 0.1<${x}$< 0.99.