Several shallow donor bound exciton photoluminescence (PL) transitions are reported in ZnO nanowires doped with carbon. The emission energies are in the range of 3360.8–3361.9 meV, close to previously reported emission lines due to excitons bound to donor point defects, such as Ga, Al, In, and H. The addition of small amounts of hydrogen during growth results in a strong enhancement of the PL of these carbon related emission lines, yet PL and annealing measurements indicate no appreciable bulk hydrogen. The observation of two electron satellites for these emission lines enables the determination of the donor binding energies. The dependence of exciton localization energy on donor binding energy departs somewhat from the usual linear relationship observed for group III donors, indicating a qualitatively different central cell potential, as one would expect for a complex. Emission lines due to excitons bound to ionized donors associated with these defects are also observed. The dependence of the PL emission intensities on temperature and growth conditions demonstrates that the lines are due to distinct complexes and not merely excited states of each other.

Ni doped, Li doped and (Li, Ni) codoped ZnO thin films were successfully grown using a pulsed laser deposition technique. Undoped and doped ZnO thin films were investigated using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES). Preliminary investigations on the Zn K-edge of the undoped and doped ZnO thin films revealed that doping has not influenced the average Zn-Zn bond length and Debye-Waller factor. This shows that both Ni and Li doping do not appreciably affect the average local environment of Zn. All the doped ZnO thin films exhibited more than 50% of substitutional Ni, with a maximum of 77% for 2% Ni and 2% Li doped ZnO thin film. The contribution of Ni metal to the EXAFS signal clearly reveals the presence of Ni clusters. The Ni-Ni distance in the Ni(0) nanoclusters, which are formed in the film, is shorter with respect to the reference Ni metal foil and the Debye-Waller factor is higher. Both facts perfectly reflect what is expected for metal nanoparticles. At the highest doping concentration (5%), the presence of Li favors the growth of a secondary NiO phase. Indeed, 2% Ni and 5% Li doped ZnO thin film shows %Nisub = 75 ± 11, %Nimet = 10 ± 8, %NiO = 15 ± 8. XANES studies further confirm that the substitutional Ni is more than 50% in all the samples. These results explain the observed magnetic properties.

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Extremely sharp low temperature photoluminescence (PL) linewidths as low as 0.17 meV are observed in nominally undoped ZnO nanowires grown by metalorganic vapour phase epitaxy (MOVPE). These are among the narrowest lines reported for ZnO PL, even for bulk growth, despite growth on highly mismatched sapphire substrates. MOVPE allows the control of group III dopants over a wide range of doping levels. At low concentrations the addition of indium and aluminum dopant resulted in the appearance of their corresponding neutral and ionized donor bound exciton transitions with linewidths comparable to those of nominally undoped material. At higher dopant levels, the axial growth rate decreases and the lateral growth rate increases for both dopants, resulting in eventual coalescence of the nanowires as well as a strong reduction in PL efficiency. The onset of lateral growth also coincides with the elimination of the so-called Y-line defect luminescence previously attributed to excitons localized at structural defects. Because of the lack of appreciable substrate induced strain, coupled with very high crystalline quality, nanowires provide an excellent tool for investigation of shallow dopant effects in ZnO by PL spectroscopy.