Structural characterization of H plasma-doped ZnO single crystals by Hall measurements and photoluminescence studies

Nominally undoped, hydrothermally grown ZnO single crystals have been investigated prior to and after doping in remote H plasma. Characterizations have been made by temperaturedependent Hall effect (TDH) and low temperature photoluminescence measurements. The H content before and after the doping has been determined using nuclear reaction analysis and is compared to the density of shallow donors derived from the TDH measurements. The electrical properties of the asgrown ZnO single crystals are found to differ significantly. This is ascribed to the density ratio of shallow donors and compensating acceptors. PL measurements showed that AlZn, GaZn, and interstitial zinc (Zni) are prominent shallow donors in the as-grown samples. Remote H plasma treatment produced a metallic conducting near-surface layer thus masking the electrical properties of the bulk. The electrical properties of the investigated samples are very similar after the treatment, independent of the as-grown state, because the density of shallow donors far exceeds that of compensating acceptors in the affected near-surface region. The maximum of the broad near-bandedge emission is found to be located at 3.3595 eV due to the high doping density.