Structural Characterization of GaN Nanowires Fabricated via Direct Reaction of Ga Vapor and Ammonia
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Structural Characterization of GaN Nanowires Fabricated via Direct Reaction of Ga Vapor and Ammonia R.N. JACOBS*, L. SALAMANCA-RIBA*, M. HE**, G.L. HARRIS**, P. ZHOU**, S. N. MOHAMMAD**, AND J.B. HALPERN** *Dept. of Materials & Nuclear Engineering. University of Maryland, College Park, MD 20742 **Materials Science Research Center of Excellence Howard University, Washington, DC 20059
ABSTRACT We report structural studies of large-scale wurtzite GaN nanowires fabricated by direct reaction of Ga vapor and NH3. This recently reported growth technique [1] demonstrates processing of GaN one-dimensional structures as thin as 26 nm and up to 500 µm in length. This method is both interesting and attractive in that fabrication is carried out without the assistance of template materials as required by other methods. In this study, transmission electron microscopy (TEM) is used to characterize the nanowires, while x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS) data provide supporting structural/compositional analysis. Our structural investigation reveals the presence of thin hexagonal platelets, which we believe play a critical role in the nucleation, growth, and orientation of the wires. In particular, our findings indicate that most of the wires grow along the [ 2110 ] direction, normal to the platelet edges.
INTRODUCTION Since Han et al. first demonstrated the synthesis of Gallium Nitride (GaN) nanorods through a Carbon Nanotube-confined reaction [2], there has been increasing interest in finding novel fabrication techniques. Nanometer sized one-dimensional structures of various materials has potential uses in the development of nanodevices and for basic mesoscopic research [3,4]. GaN is particularly promising due to its large band-gap and high melting point, and is already being used in blue LEDs, laser diodes, and for high temperature electronic devices. Following Han’s publication in 1997, Cheng et al demonstrated the synthesis of wurtzite GaN in alumina membranes [4]. In addition, Duan et al [5], grew pure [ 0110 ] oriented wires using a laser-assisted catalytic method. Here, laser ablation of a GaNcatalytic metal composite target generated reactive sites confining and directing the growth of crystalline wires. There has now been a growing number of reports on methods to fabricate nanowires of GaN and other materials [6-10]. However, these methods have all required the use of catalysts or templates. The technique used in this work (described in the next section) demonstrates a catalyst/template free nanowire fabrication route through the direct reaction of Ga and flowing Ammonia in a tube furnace. EXPERIMENT The schematic diagram shown in Figure 1, illustrates the basic experimental set-up used in this work. Approximately 3 g of pure Ga metal was placed in a Boron Nitride boat which was set at the bottom of a horizontal oven. The tube of the oven was lined with a W9.4.1
Quartz Liner
Oven (850-900°C)
Cooled Cu Block
Ga Pump
NH3 Quartz tube
BN Boat
Figure 1. Experimental set-up for direct
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