Catalyst-Free GaN Nanowire Nucleation: Correlation of Temperature-Dependent Nanowire Orientation and Growth Matrix Chang
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1206-M11-42
Catalyst-Free GaN Nanowire Nucleation: Correlation of Temperature-Dependent Nanowire Orientation and Growth Matrix Changes
Kaylee McElroy1, Virginia M. Ayres1, Thomas R. Bieler1, Benjamin W. Jacobs1,2, Martin A. Crimp1 1
College of Engineering, Michigan State University, East Lansing, MI 48824-1226, U.S.A.
2
Present address: Sandia National Laboratories, Livermore, CA 94551-0969, U.S.A.
ABSTRACT Growth orientation and type of internal structures are both observed to change abruptly as a function of growth temperature in catalyst free growth of gallium nitride nanowires. In the present work, corresponding temperature-dependent changes in the growth matrix substrate that can affect the availability of nucleation sites and influence the reactivity of constituent adatom materials in catalyst-free nanowire growth are investigated. The influence of Ga vapor pressure and an abrupt change in the availability of single versus molecular adatom constituents is identified as a possible controlling parameter. INTRODUCTION Gallium nitride (GaN) nanowires have been under extensive investigation in recent years due to their unique optical [1] and electrical properties [2] as well as their potential advantages in enabling new device applications [3, 4]. For device applications, control of crystalline quality and orientation is essential. To develop controlled nanowire growth processes, it is critical to understand nanowire nucleation and growth mechanisms. The nanowires examined in this study were grown using a catalyst-free growth method [5] at furnace growth temperatures of 850°C, 950°C and 1000°C. Catalyst free nanowire growth [5,6,7,8] results in no metal impurities in the nanowires and can be used in applications where device fabrication steps are incompatible with the presence of a metal catalyst [9, 10]. In previously reported work [11,12,13], we demonstrated that the nanowire growth orientation was influenced by growth temperature. Between 950°C to 1000°C, an abrupt change in wurtzite growth orientation from 112 0 to ⟨0001⟩ is observed. We further reported that the GaN nanowires had internal structures that continued along the entire length of the nanowires. The majority of nanowires grown at 850°C and 950°C had multiphase wurtzite and zinc-blende crystalline domains that persisted along the entire nanowire length. The growth direction was € ⟨110⟩ for the zinc-blende domains and 112 0 for the wurtzite domains as stated. Very recently, zinc-blende/wurtzite multi-domain GaN nanowires have been reported by another group [14]. In contrast, the majority of nanowires and rods grown at 1000˚C were single-phase wurtzite with a ⟨0001⟩ growth orientation and a different internal structure consisting of a single nanopipe [13]. A nanopipe can develop from€relaxation of a large Burgers vector screw dislocation [15]. While
ours is the first reported observation of nanopipe formation in the GaN nanowire system, evidence for formation of an internal screw dislocation in the related PbS nanowire system has been reported b
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