Temperature dependent (4.2–300 K) photoluminescence (PL) of bulk (0001)-oriented ZnO in the range of free- and bound-exciton emission is presented. Emission from several bound excitons and the free A exciton were observed from the low temperature (20 K) PL spectrum. The temperature dependence of the free-exciton peak position was fit using the Manoogian-Woolley equation and the coefficients obtained show reasonable agreement both with first-principle theoretical calculations and empirical values of the coefficients for other II–VI semiconductors. The strongest bound-exciton line with a width (full width at half maximum) of about 1 meV exhibited a thermal activation energy of approximately 14 meV, consistent with the exciton-defect binding energy. It was not observed at temperatures above 150 K. Additional analysis of this particular bound-exciton peak suggests it dissociates into a free exciton and a neutral-donor-like defect-pair complex with increasing temperature.

We report the preparation of ZnO nanocrystals embedded in a SiO2 matrix formed using sequential zinc and oxygen ion implantations. The optical absorption spectra and photoemission spectra of zinc implanted and zinc/oxygen coimplanted silica show that the first zinc implantation produces zinc clusters and that the subsequent oxygen implantation following the zinc implantation rearranges the distribution of zinc and oxygen ions at an atomic level. While thermal annealing of Zn only implanted silica leads to the formation of Zn nanocrystals, thermal annealing of zinc/oxygen coimplanted silica promotes the growth of ZnO nanocrystals. The absorption and photoluminescence spectra show that ZnO nanocrystals form in an amorphous SiO2 matrix and that their systematic change as a function of annealing temperature corresponds to the typical correlation between the increase of particle size and a redshift in near-band-edge emission.

The effects of mechanical polishing on the photoluminescence (PL) from each polar face of wurtzite-structure ZnO are presented. Differences observed for the 4.2K PL of a mechanically polished surface when compared to that of a chemomechanically polished surface include broadened bound-exciton peaks, hot-exciton luminescence, and a donor-acceptor pair peak at 3.2108eV. Analysis of this donor-acceptor pair peak results in estimated donor and acceptor ionization energies of 52±10 and 230±10meV, respectively, with a mean separation distance between pairs of approximately 3–4nm. The donors and acceptors are attributed to point defects introduced by dislocation motion during the polishing process and identified as octahedral Zn interstitials and Zn vacancies, respectively.

The optical and structural properties of H or He implanted ZnO were investigated using low temperature photoluminescence (PL) and infrared spectroscopy (IR). H implantation is shown to influence the relative luminescence intensities of the donor bound excitons, enhancing the 3.361 eV peak, and changing the overall intensity of the PL spectrum. PL from He implanted ZnO is used to demonstrate that implantation damage is partially responsible for the variations observed in the PL of H implanted ZnO. IR spectra show that the increase in the relative intensity of the 3.361 eV peak coincides with an appearance of the H vibrational mode in the ZnO lattice. Our results indicate that the implanted H forms O–H bonds at Zn vacancies, and that it is these defect complexes which give rise to the shallow donors participating in the observed bound-exciton luminescence at 3.361 eV.

A study of the effects of chemomechanical polishing on the room temperature photoluminescence of both polar faces of ZnO single crystals is presented. A distinct peak which we associate with second order exciton-phonon (FX-2LO) emission and which dominates the LO emission for both (0001) and (000 1 1) etched surfaces is observed. Chemomechanical polishing results in reduction of the distinct FX-2LO peak, and an increase in the relative importance of first order exciton-phonon (FX-1LO) emission. We attribute this to disorder introduced by the polishing process.Introduction The recent availability of high crystalline quality bulk ZnO presents new possibilities for short wavelength light emitters. Chemomechanical polishing is typically used in substrate preparation prior to epitaxial growth for creating flat surfaces with minimum roughness and subsurface damage. In this work, we examined the effects of chemomechanical polishing on the room temperature (RT) photoluminescence (PL) of both polar faces of undoped ZnO single crystals.