Improving the composition uniformity of Au-catalyzed InGaAs nanowires on silicon Jae Cheol Shin a , Do Yang Kim b,c , Ari Lee a , Hyo Jin Kim a , Jae Hun Kim c , Won Jun Choi c , Hyun-Seok Kim d , Kyoung Jin Choi b,n a Korea Photonics Technology Institute, Gwangju 500-779, South Korea b School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science & Technology (UNIST), Ulsan 689-805, South Korea c Korea Institute of Science and Technology (KIST), Seoul 136-791, South Korea d Electronics and Electrical Engineering, Dongguk University, Seoul 100-715, South Korea article info Article history: Received 26 December 2012 Received in revised form 19 February 2013 Accepted 23 February 2013 Communicated by K. Deppert Available online 4 March 2013 Keywords: A1. Nanostructures A3. Metalorganic vapor phase epitaxy B1. Nanomaterials B2. Semiconducting III–V materials abstract Spatial distribution of indium (In) atoms in ternary In x Ga 1x As nanowires (NWs) was investigated by the energy-dispersive X-ray spectroscopy, which were grown on Si (111) by metal-organic chemical vapor deposition. The NWs have a tapered morphology with thicker diameter and higher In composition in the bottom of NWs. However, decreasing growth temperature and V/III ratio resulted in straight NWs with constant In composition throughout the NWs. This was attributed to enhanced deposition on the sidewall of the NW with higher In composition through the vapor–solid mode, leading to a core-shell structure consisting of low and high In-content layers. & 2013 Elsevier B.V. All rights reserved. 1. Introduction One-dimensional (1-D) nanostructures such as nanorods, nanowires (NWs), and nanobelts have been successfully synthe- sized using a wide range of semiconductors and demonstrated new design concepts for novel electronic and optoelectronic devices. Especially, hetero-structured 1-D nanostructures, includ- ing coaxial core-shell, axially-modulated, and alloyed NWs, have attracted much attention because of their controlled morpholo- gies and multi-functional optoelectronic properties [1–4]. Among them, alloyed semiconductor NWs can offer more unique proper- ties than the corresponding elemental or binary ones by engi- neering the bandgap energy, which is one of the most important parameters of a semiconductor and determines its electronic and optical properties [5–8]. III–V compound semiconductor NWs based on binary materials (e.g., GaAs, InP, GaN) have been fabricated for optical devices such as solar-cells and light- emitting-diodes [9,10]. For example, the ternary In x Ga 1 x As can cover the wavelength range from near- to mid-infrared (0.87– 387–3.5 mm) by adjusting indium (In) composition, as demon- strated by the heterojunction solar cells [8] and light-emitting diodes (LEDs) for medical applications [11]. Several recent works had reported the successful growths of high quality III-V semiconductor NWs by using selective-area epitaxy (SAE) in metal-organic chemical vapor deposition (MOCVD) reactor [12–14]. In the SAE-grown NWs, the growths were defined by the openings formed by various lithography methods resulting in highly-order NWs [12–14]. The fabrication of these patterns had been reported by using electron-beam lithography, and other self-assembled lithography methods (i.e. 2-D close-packed mono- layer colloidal deposition [15,16], or diblock-copolymer methods [17,18]). Vapor–liquid–solid (VLS) method, which facilitates one- dimensional (1-D) crystallization using metal catalyst, is also well-known method to synthesize semiconductor NWs [19,20]. The ternary NWs grown via VLS method, however, are suffered from large variation of the alloy composition along the NW height [4,21]. For example, the In composition of the ternary In x Ga 1 x As NW varies from 0.2 to 0.6 with NW position [4]. Formation of ternary In x Ga 1 x As NW as a result of gallium (Ga) diffusion from GaAs substrate have shown relatively uniform alloy composition along the NW height [22]. However, the tunable range of the alloy composition is very limited (i.e., x ¼ 0.81–1). In this paper, we have investigated the distribution of In atoms in the ternary In x Ga 1 x As NWs grown at different process para- meters such as growth temperature and V/III ratio, aiming to minimize the composition variation of the NW. In addition to the VLS, we have found that vapor–solid (VS) growth mechanism played important role for the composition variation along the NW heights. The VS growth mechanism is nearly deactivated with the decrease of growth temperature and V/III ratio, resulting in Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2013.02.025 n Corresponding author. E-mail address: choi@unist.ac.kr (K.J. Choi). Journal of Crystal Growth 372 (2013) 15–18