Morphology, structure and optical properties of MOCVD grown pseudo-binary alloy nanowires of Zn 1-x Cd x Se on Si and Ga
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Morphology, structure and optical properties of MOCVD grown pseudo-binary alloy nanowires of Zn1-xCdxSe on Si and GaAs substrates C. M. Ng, C. X. Shan, Z. Liu and S. K. Hark Department of Physics, The Chinese University of Hong Kong, Hong Kong ABSTRACT Long and fine Zn1-xCdxSe pseudo-binary alloy nanowires of various compositions x covering the entire range were grown by metalorganic chemical vapor deposition, using diethlyzinc, dimethylcadmium and diisopropylselenide as precursors, on Si (100) and GaAs (100) substrates; sputtered gold was used as a catalyst to promote nanowire formation. By controlling the ratio of the flows of the precursors, the temperature and the pressure during growth, we obtained nanowires of desired compositions. The morphology, structure and optical properties of the nanowires were studied by various techniques, including secondary electron microscopy, atomic force microscopy, transmission electron microscopy, X-ray diffraction, photoluminescence, and Raman scattering. Depending on the substrate, composition and conditions of growth, either the zincblende or wurtzite nanowires were obtained. At compositions where the stable form would have been normally wurtzite, the zincblende form could be obtained under certain growth conditions. From the orientations of the ordered nanowires on the substrate surface, their directions of growth were deduced and confirmed by high resolution lattice imaging. The relationship between the band gap and the composition of the nanowires were measured and found to deviate from that of bulk alloys and epilayers. The interplay between the growth conditions and compositions and morphology of the nanowires are discussed. INTRODUCTION One-dimensional semiconductor nanostructures, such as nanowires and nanotubes, have great potential in the construction of nano-scaled electronic and optoelectronic devices [1-3]. The fabrications of group IV, III-V, and II-VI semiconductor nanowires have been demonstrated by various methods [4]. A large portion of work reported so far has been concentrated on elemental and binary compound semiconductor systems, such as Si, Ge, GaAs, ZnO, GaP and ZnS [5-8]; with only limited studies on alloy systems or tertiary compounds [9-11]. As far as we know, growth of ternary compound nanowires of variable compositions has not been reported. In this paper, we show the successful growth of Zn1-xCdxSe alloy nanowires over the entire composition range by metalorganic chemical vapor deposition (MOCVD) via a control of the partial pressures and flow rates of the vapors of precursors. Both the composition of the nanowires and the substrate on which they grow influence their morphology and structure; but the substrate effect dominates. ZnSe and CdSe are both attractive candidates for visible optoelectronic devices, due to their 2.69eV and 1.66eV bandgap energies at room temperature. Successfully controlling the compositions of alloy nanowires has the potential of developing new full color emitting or absorbing nanodevices. We found that the nano
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