Controlled Growth and Electronic Properties of Gallium Nitride Nanowires
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Controlled Growth and Electronic Properties of Gallium Nitride Nanowires Song Han, Wu Jin, Tao Tang, Chao Li, Daihua Zhang, Xiaolei Liu and Chongwu Zhou Department of Electrical Engineering – Electrophysics University of Southern California Los Angeles, CA 90089 – 0271 ABSTRACT High-quality single crystalline gallium nitride (GaN) nanowires are synthesized via a chemical vapor deposition (CVD) method using gold nanoparticles as the catalyst. This method enables control over several important aspects of the growth, including control of the nanowire diameter by using mono-dispersed gold clusters, control of the nanowire location via e-beam patterning of the catalyst sites, and control of the nanowire orientation via epitaxial growth on aplane sapphire substrates. Transport properties of these GaN nanowires are studied. Our work opens up new ways to use GaN nanowires as nano-building blocks. INTRODUCTION III-V nitride semiconductors have attract enormous attention in the past decade due to their exciting properties [1,2]. GaN is particularly interesting as its large direct band-gap (3.4eV) makes it ideal for blue light-emitting applications. A variety of devices based on GaN thin films have been demonstrated, including blue light emitting diodes (LEDs) [3] and laser diodes [4]. In contrast, research on GaN nanowires has not reached the same extent. Many groups have synthesized GaN nanowires using various techniques 32[5-13]; however, controlled growth of GaN nanowires of predetermined diameters remains a challenging issue, presumably because of the difficulty associated with producing mono-dispersed Fe or Ni catalyst clusters. An additional common feature of previous work is that GaN nanowires were usually grown all over the surface and entangled together. Controlled growth of individual GaN nanowires at predetermined sites has not been demonstrated. Here we report a CVD method which enables control over several important aspects of the growth, including control of the nanowire diameter by using monodispersed gold clusters, control of the nanowire location via e-beam patterning of the catalyst sites, and control of the nanowire orientation via epitaxial growth on a-plane sapphire substrates. The preparation of the GaN nanowires is briefly described as follows. Gallium source (99.9999%, Alfa Aesar) was put in the middle of the furnace. A Si/SiO2 substrate coated with Au nanoparticals was placed about 1 inch at the downstream of the Ga source. This quartz tube was heated to 900˚C. The reaction was carried out by flowing anhydrous NH3 gas through the quartz tube at 30 standard cubic centimeters per minute (sccm) for ten minutes. After the system cooled down, the Si/SiO2 substrate was found to be coated with a layer of white material, which was confirmed to consist of GaN nanowires by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). Our synthesis is based on the VLS growth mechanism, where the Ga vapor first diffuses into the gold catalytic
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