Influence of growth parameters on In-droplet-assisted growth of InAs nanowires on silicon

Applied Nanoscience, Aug 2017

The influence of growth parameters on the morphology and density of InAs nanowires (NWs) grown on bare Si substrates using Indium (In) droplets as catalyst is investigated. By tuning the growth temperature, V/III flux ratio, and growth rate, the diameter and yield of as-grown NWs were controllably manipulated. It is demonstrated that the In-droplet-assisted growth of InAs NWs can only be realized on bare Si within a relatively narrow growth window of 420–475 °C. Below 420 °C, NWs’ growth is kinetically limited, while the highest yield of vertically aligned NWs was obtained at ~450 °C. It is shown that In-catalyzed InAs NWs nucleation can only be realized on Si at highly As-rich conditions (V/III flux ratio >50), while the axial growth rate was found to be strongly dependent on the V/III flux ratio. The nucleation and axial growth of In-catalyzed InAs NWs are promoted by a low growth rate, while a high growth rate favors the formation of unwanted parasitic islands.

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Influence of growth parameters on In-droplet-assisted growth of InAs nanowires on silicon

Influence of growth parameters on In-droplet-assisted growth of InAs nanowires on silicon Ezekiel A. Anyebe 0 1 0 Federal University of Agriculture , PMB 2373, Makurdi , Nigeria 1 & Ezekiel A. Anyebe The influence of growth parameters on the morphology and density of InAs nanowires (NWs) grown on bare Si substrates using Indium (In) droplets as catalyst is investigated. By tuning the growth temperature, V/III flux ratio, and growth rate, the diameter and yield of asgrown NWs were controllably manipulated. It is demonstrated that the In-droplet-assisted growth of InAs NWs can only be realized on bare Si within a relatively narrow growth window of 420-475 C. Below 420 C, NWs' growth is kinetically limited, while the highest yield of vertically aligned NWs was obtained at *450 C. It is shown that In-catalyzed InAs NWs nucleation can only be realized on Si at highly As-rich conditions (V/III flux ratio [50), while the axial growth rate was found to be strongly dependent on the V/III flux ratio. The nucleation and axial growth of In-catalyzed InAs NWs are promoted by a low growth rate, while a high growth rate favors the formation of unwanted parasitic islands. InAs; Nanowires; Semiconductors; Molecular beam epitaxy Introduction Semiconducting nanowires (NWs) have been touted as promising building blocks for applications in photonics and electronic devices (Duan et al. 2003; Tian et al. 2007; Colinge et al. 2010; Tomioka et al. 2012; Wang et al. 2014) due to their unique properties including superior light absorption, enhanced photo-carrier separation, and epitaxial growth insensitive to lattice mismatch (Wei et al. 2009) . In particular, InAs NWs have garnered enormous research interest due to its narrow direct band gap (0.35 eV), small electron effective mass, and high electron mobility of *30,000 cm2/Vs at 300 K (Wallart et al. 2005; Ihn and Song. 2007) with potential for applications in high-speed electronics and mid-infrared optoelectronic devices (Dimakis et al. 2011) . The monolithic integration of NWs with Si has recently attracted enormous research interest to exploit the low-cost and scalability of the well-established Si platform as well as the fascinating electronic and optoelectronic properties of NWs. Although, Au is commonly used for NWs nucleation, its use is accompanied with the introduction of unwanted impurities and deep level traps (Allen et al. 2008) , which are detrimental to applications in optoelectronic devices (Bar-Sadan et al. 2012) . Consequently, there is a paradigm shift towards Au-free technologies including catalyst-free (Wei et al. 2009; Dimakis et al. 2011; Hwang et al. 2015) and droplet-assisted growth (DAG) of NWs (Somaschini et al. 2013; Anyebe et al. 2014; Ermez et al. 2015) . Whereas catalyst-free growth is Indium (In) free and requires no catalyst for NWs nucleation, droplet-assisted growth involves the in situ deposition of group-III element droplets (mostly Ga or In seeds) on the substrate prior to growth initiation to function as catalyst for the preferential nucleation of NWs. DAG growth is not only impurity-free and compatible with the complementary metal-oxide semiconductor (CMOS) platform (Glas et al. 2013) , it also allows for the precise control of NWs density (Somaschini et al. 2013; Anyebe et al. 2014; Ermez et al. 2015) , which is highly essential for applications in functional optoelectronic nanodevices. For instance, the electron mobility (Ford et al. 2009a, b; Abul Khayer and Lake 2010) and light absorption (Krogstrup et al. 2013; Heiss et al. 2014) , and hence performance of transistors and solar cells, respectively, have been shown to be strongly dependent on the NWs diameter. It is well established that the size and density of NWs can be controllably manipulated by tuning basic growth precursors (Anyebe et al. 2017; Li et al. 2017) . Various growth strategies have been employed for the growth parameter studies of InAs NWs including selective area growth (SAG) (Mandl et al. 2011; Bjoerk et al. 2012) , catalyst-free growth on SiOx-coated substrates (Hertenberger et al. 2010; Koblmu¨ ller et al. 2010; Madsen et al. 2011) , and Au-catalyzed growth (Dayeh et al. 2007; Tchernycheva et al. 2007; Babu and Yoh 2011; Zhang et al. 2016) . An investigation of the influence of growth parameters on In-droplet-assisted InAs NWs grown on Si would unravel the conditions for realizing optimal NWs with the highest density and aspect ratio as well as enable for the predictable and reproducible fabrication of high performance, and impurity-free nanoelectronic devices compatible with the CMOS technology. However, despite the significant influence of In-rich conditions (and in effect the predeposition of In droplets) on the NWs geometry (Jung et al. 2014; Zhang et al. 2014) resulting from strong differences in adatom kinetics compared to other growth techniques, little is known about the influence of growth parameters on the morphology an (...truncated)


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Ezekiel A. Anyebe. Influence of growth parameters on In-droplet-assisted growth of InAs nanowires on silicon, Applied Nanoscience, 2017, pp. 1-6, DOI: 10.1007/s13204-017-0585-8