Direct Evidence for As as a Zn-Site Impurity in ZnO

Arsenic has been reported in the literature as one of the few $p$-type dopants in the technologically promising II-VI semiconductor ZnO. However, there is an ongoing debate whether the $p$-type character is due to As simply replacing O atoms or to the formation of more complicated defect complexes, possibly involving As on Zn sites. We have determined the lattice location of implanted As in ZnO by means of conversion-electron emission channeling from radioactive ${}^{73}\mathrm{As}$. In contrast to what one might expect from its nature as a group V element, we find that As does not occupy substitutional O sites but in its large majority substitutional Zn sites. Arsenic in ZnO (and probably also in GaN) is thus an interesting example for an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system.