ZnO nanostructures were grown by PLD on c-sapphire, Si (111) (n-type and p-type), steel and ZnO substrates and analysed using SEM, XRD and PL techniques. Under optimised growth conditions, self-forming arrays of vertically aligned nanostructures were obtained.  SEM studies revealed two main structures: nanocolumns and a “moth-eye type” array of nanocones, which gave a graded effective refractive index [2].

XRD measurements indicate that both types of structures were well crystallized and highly oriented along the c-axis. nZnO/pSi heterojunction LEDs formed using the nanocone arrays gave rectification and blueish-white electroluminescence [2]:

The sample photoluminescence was investigated using above band gap excitation. Low temperature PL spectra for nanocolumns grown on sapphire and n-type Si (111) show an emission which is similar to that observed for bulk ZnO with a spectrum dominated by donor bound exciton recombination at ~3.36 eV and a structured green band. The PL intensity was particularly enhanced for nanocone structures grown on the cubic Si substrate. For these samples, besides the usual PL lines observed both in ZnO bulk and in nanocolumns grown on sapphire, additional features were observed at 3.12 eV, 3.02 eV and 2.92 eV which follow a vibronic progression of 100 meV. The analysis of these new lines and a correlation with the growth parameters and structural analysis will be discussed.

[1] Sandana et al., accepted for publication J. Vac. Sci. Technol. (2009)

[2] Rogers et al. Proc. SPIE Vol. 7217 08 pp1-8 (2009)

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