Shallow acceptor complexes in p-type ZnO

ZnO films grown on sapphire substrates by organometallic vapor phase epitaxy exhibit p-type behavior when sufficient N is properly incorporated and followed by an appropriate annealing sequence. While substitutional N on the O sublattice is a deep acceptor, shallow acceptor complexes involving N, H and V$_{Zn}$ can provide useful 10$^{18}$ cm$^{-3}$ p-type films. Taking advantage of Raman, SIMS, and Hall-effect data, we establish a two-step growth scheme to form a metastable double donor complex, N$_{{\mathrm{Zn}}^-}$V$_{\mathrm{O}}$, then convert it to a single shallow acceptor complex, V$_{{\mathrm{Zn}}^-}$N$_{\mathrm{O}^-}$H$^{+}$ during \textit{in situ} annealing in N$_{2}$O. The V$_{{\mathrm{Zn}}^-}$N$_{\mathrm{O}^-}$H$^{+}$ complex accepts electrons at ionization energies of 134 meV, rendering it an efficient p-type dopant at room temperature.