Controlled Growth and Characterization of Non-tapered InN Nanowires on Si(111) Substrates by Molecular Beam Epitaxy
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1178-AA01-12
Controlled Growth and Characterization of Non-tapered InN Nanowires on Si(111) Substrates by Molecular Beam Epitaxy Y.-L. Chang, A. Fatehi, F. Li, and Z. Mi Department of Electrical and Computer Engineering, McGill University 3480 University Street, Montreal, Quebec H3A 2A7, Canada
ABSTRACT We have performed a detailed investigation of the molecular beam epitaxial (MBE) growth and characterization of InN nanowires spontaneously formed on Si(111) substrates under nitrogen rich conditions. Controlled epitaxial growth of InN nanowires (NWs) has been demonstrated by using an in situ deposited thin (~ 0.5 nm) In seeding layer prior to the initiation of growth. By applying this technique, we have achieved non-tapered epitaxial InN NWs that are relatively free of dislocations and stacking faults. Such InN NW ensembles display strong photoluminescence (PL) at room temperature and considerably reduced spectral broadening, with very narrow spectral linewidths of 22 and 40 meV at 77 K and 300 K, respectively. INTRODUCTION InN NWs and whiskers grown directly on Si substrates have attracted considerable attention of late. Among group III-nitrides, InN has the narrowest bandgap (~ 0.7 eV), the highest electron mobility and saturation velocity, as well as the smallest effective mass, which make it a nearly ideal material for a new class of nanoelectronic and nanophotonic devices [1-14]. The low toxicity [15] and the presence of an electron accumulation layer on InN NW surface [16] also make it a potential candidate for biosensing applications. Furthermore, the bandgap and the absorption spectrum of InGaN alloys can be continuously tuned from ~ 0.7 eV to 3.4 eV by varying In or Ga compositions, providing an almost perfect match to the solar spectrum. Therefore, InGaN may also emerge as the material of choice for low cost, high efficiency multijunction solar cells [17]. In terms of epitaxial growth of InN NWs, two general methods have been utilized. The first method involves the use of a foreign metal (typically Au) catalyst via the vapor-liquid-solid (VLS) mechanism [18, 19]. This widely used method has a drawback induced by metal impurity contamination, which can alter the bandstructure of the wire material and hinder device performance. Alternatively, InN NWs can also be spontaneously formed under nitrogen rich conditions [20]. In this case, even though no foreign metal catalyst is used, it is believed that the NWs may be formed via a self-catalytic VLS process [7, 8, 21], wherein nano-scale liquid droplets of the constituting metal element of the wire material act as catalysts that promote the NW nucleation and growth [14]. Common in both approaches, InN NWs grown exhibit a tapered morphology [7, 9, 14], or a variation in diameter along the length of the wire, which leads to uncontrolled electrical and optical properties and thus severely limits practical device applications. This difficulty in achieving high structural quality InN NWs may be partially attributed to the low decomposition temperature (~ 500 – 600 o
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