Hall effect studies of donors and acceptors in different types of bulk ZnO modified by annealing and hydrogen implantation

Samples of as-manufactured and annealed zinc oxide (ZnO) grown by melt-growth, seeded chemical vapour transport (SCVT) growth and hydrogen-implanted hydrothermal ZnO were investigated via the temperature dependent Hall technique. The conduction in the melt-grown sample appeared to be dominated by two donors with activation energies of about 70 meV and 44 meV, the former disappearing with annealing above 550 oC. Only one dominant donor of about 80 meV was found in the SCVT-grown sample and it showed little change with annealing. Surface conduction effects were observed only in the SCVT-grown sample. Hydrogen-implanted hydrothermal ZnO layers were found to have only one dominant donor with activation energy of about 45 meV that was stable up to annealing temperatures of about 300 oC. The acceptor concentration was found to increase considerably with annealing above 300 oC. We attempt to interpret these results by considering theoretical predictions for the various native and extrinsic defects expected to occur in our samples. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)