Elsevier

Journal of Crystal Growth

Volume 372, 1 June 2013, Pages 15-18
Journal of Crystal Growth

Improving the composition uniformity of Au-catalyzed InGaAs nanowires on silicon

https://doi.org/10.1016/j.jcrysgro.2013.02.025Get rights and content

Abstract

Spatial distribution of indium (In) atoms in ternary InxGa1−xAs 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.

Highlights

► We study the growth mechanism of the composition variation in the InGaAs nanowires. ► Indium distribution in the InGaAs nanowires was investigated by the X-ray analysis. ► We grow the ternary InGaAs nanowires having uniform alloy composition.

Introduction

One-dimensional (1-D) nanostructures such as nanorods, nanowires (NWs), and nanobelts have been successfully synthesized using a wide range of semiconductors and demonstrated new design concepts for novel electronic and optoelectronic devices. Especially, hetero-structured 1-D nanostructures, including coaxial core-shell, axially-modulated, and alloyed NWs, have attracted much attention because of their controlled morphologies and multi-functional optoelectronic properties [1], [2], [3], [4]. Among them, alloyed semiconductor NWs can offer more unique properties than the corresponding elemental or binary ones by engineering the bandgap energy, which is one of the most important parameters of a semiconductor and determines its electronic and optical properties [5], [6], [7], [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 InxGa1−xAs can cover the wavelength range from near- to mid-infrared (0.87–387–3.5 μm) by adjusting indium (In) composition, as demonstrated 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], [13], [14]. In the SAE-grown NWs, the growths were defined by the openings formed by various lithography methods resulting in highly-order NWs [12], [13], [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 monolayer 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 InxGa1−xAs NW varies from 0.2 to 0.6 with NW position [4]. Formation of ternary InxGa1−xAs 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=0.81–1).

In this paper, we have investigated the distribution of In atoms in the ternary InxGa1−xAs NWs grown at different process parameters 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 single-crystalline, ternary InxGa1−xAs NWs possessing very uniform alloy composition along the NW height.

Section snippets

Experimental methods

Metal-organic chemical vapor deposition (MOCVD, Aixtron inc.) with horizontal reactor has been used for the growth of InxGa1−xAs NWs. For the growth, p-type Si (111) wafer were immersed in poly-L-lysine (PLL) solution (Sigma-Aldrich inc.) for 2 min, rinsed in deionized water for 10 s and dried with N2 gun. Thin PLL layer which is positively charged promotes the uniform distribution of Au nanoparticles (NPs) on Si surface by preventing the agglomeration of negatively charged Au NPs [23].

Results and discussion

Fig. 1(a–c) shows the SEM images of ternary InxGa1−xAs NWs on Si (111) substrate grown at 440, 470, and 500 °C, respectively. One can see that most InxGa1−xAs NWs were vertically grown on the substrate. The number density of the NWs is in the range of 1–5×107/cm2 while that of the Au nanoparticles is 2×109/cm2. The surface of Si is known to be easily oxidized upon exposure to air. The de-oxidation process performed by a thermal annealing at 620 °C under H2 ambient was found to be an important

Conclusion

In summary, we have investigated the effects of growth temperature and V/III ratio on the morphology and group-III composition of ternary InxGa1−xAs NWs by using EDX and TEM analysis. The VS growth mode is strongly related to the In composition variation along the NW height as well as tapered shape of the NWs. By optimizing the growth parameters, we have demonstrated the single crystalline ternary InxGa1−xAs NWs via VLS growth mode. The In composition of the NWs is very uniform along the NW

Acknowledgment

This research was supported by Future-based Technology Development Program (Nano Fields, grant number: 2010-0029300) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology.

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