科研之友
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摘要
ZnO nanopillars are often grown on various substrates by catalytic growth processes through a vapor-liquid-solid (VLS) mechanism. However, on silicon substrates, even with the catalyzed growth processes, it is still very difficult to obtain highly oriented ZnO nanopillar arrays. In this work, it was found that in most cases the actual growth process of ZnO on Si catalyzed by Au was not of real VLS character. In the initial growth stage, the substrate surface is partially melted and then oxidized into a very thin layer of SiO2. Zn-rich alloys instead of ZnO are first deposited on the SiO2/Si substrates and form polycrystalline hillocks in an atmosphere with low O-2 partial pressure. The difficulty for ZnO to nucleate on SiO2/Si is another reason preventing ZnO nanopillars from growing epitaxially on the substrates. Defects, steps, and/or stress on the substrate surfaces may support the nucleation process and thus may influence the initial growth stage and the control of the growth orientation of the pillars. With the help of scratches on Si substrates and by avoiding the formation of hillocks, well-aligned ZnO nanopillars were obtained both on Si (111) and (100) surfaces. Sharp photoluminescence (PL) peaks of bound exciton emissions and a free exciton emission were detected at low temperature. An unreported PL peak at about 3.367 eV and in some cases a donor-acceptor-pair transition at about 3.308 eV were also found. At higher temperature, a band-acceptor recombination process together with strong LO-phonon replicas occurred. A donor dopant concentration N-D of about 5.7x10(18) cm(-3) and an acceptor ionization energy of 126 +/- 2 meV were evaluated from the spectra.
- 出版日期2006-3-1
