Optical investigations on the annealing behavior of gallium- and nitrogen-implanted ZnO

Abstract

Gallium and nitrogen ions have been implanted into ZnO crystals and metal organic vapor phase epitaxy grown ZnO layers. Postimplantation annealing behavior in the temperature range between 200 and 900 °C has been studied by means of Raman scattering and low-temperature photoluminescence. The temperature for healing of the implantation-induced defects was found to be 800 °C. Implanted gallium acts as donor with a donor binding energy ED of 53 meV, thus allowing the control of n-type doping in ZnO. From photoluminescence measurements of the donor-acceptor pair transition of a series of nitrogen-implanted ZnO samples we estimate the binding energy EA of the nitrogen acceptor between 163 and 196 meV. Electrical characterization of nitrogen-implanted samples shows a behavior ranging from low n-type to highly compensated. But no unambiguous and reproducible type conversion could be achieved.

Absence of ferromagnetic order in high quality bulk Co-doped ZnO samples

“…21 Nevertheless, crystalline disorder due to impurities or defects can result in the amplification of those modes due to the breaking out of the k-conservation law, giving rise to a broad band that reflects the density of phonon states around those frequencies, as observed for Ga implanted ZnO. 22 In our samples, Co atoms are also expected to introduce disorder in the crystal, which can explain the emergence of the broad band. For the sample with x = 0.04, the E 2 ͑H͒ peak is dominant, but as the Co composition increases, the broad band becomes the dominant feature of the Raman spectra, the inset of Fig.…”

Isotopic study of the nitrogen-related modes in N+-implanted ZnO

“…8͒ or to intrinsic host lattice defects. 9 Also, the correlation between N concentration and the intensity of the additional peaks has been confirmed by some works 8,10 and contradicted by others. 9 In a recent study, 10 on the basis of a local phonon density of states calculation, it was suggested that the additional mode observed at 275 cm −1 originates from localized vibration of the Zn atoms in a first-neighbor environment where part of the O atoms are replaced by N atoms.…”

“…The band between 520 and 600 cm −1 is due to disorder-activated longitudinal optical ͑DALO͒ modes and reflects the lattice disorder in the implanted layer. 8 To facilitate the comparison between the spectra of the implanted layers, the spectra shown in Fig. 1 have been normalized so that all of them display a similar DALO intensity.…”

Electron paramagnetic resonance and photo-electron paramagnetic resonance investigation on the recharging of the substitutional nitrogen acceptor in ZnO

“…4,5 To our knowledge, the isolated nitrogen acceptors were never observed in intentionally doped epitaxial films or single crystals, although evidence for the presence of high concentrations of nitrogen was obtained by other characterization methods. [6][7][8] For the EPR experiments on the N centers the samples had to be illuminated by light to convert them to the paramagnetic charge state (N 0 ). [1][2][3] This illumination was needed because residual shallow donors were present in the samples causing the nitrogen centers to be in the negative EPR inactive charge state (N À ).…”