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.

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.

High-resolution photoluminescence (PL) experiments show that Sb doped ZnO nanowires exhibit shallow donor bound exciton (D0X) transitions at 3364.3 meV, which is shallower than the well-known In, Ga, Al, and H D0X transitions. The relative intensity of the Sb D0X transition scales with dopant concentration. Temperature dependent PL measurements show that the Sb D0X behaves like other D0X transitions with a thermal activation energy close to the spectroscopic binding energy. No evidence of an ionized donor bound exciton (D+X) is observed, consistent with the expectation from Haynes' rule that such a state would have a higher energy than the free exciton.