Microstructural properties and formation mechanisms of GaN nanorods grown on Al 2 O 3 (0001) substrates

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Young Hae Kwon and Tae Won Kang Quantum Functional Semiconductor Research Center, Dongguk University, Seoul 100-715, Korea

Dong Hun Kim, Dea Uk Lee, and Tae Whan Kima) Advanced Semiconductor Research Center, Division of Electronics and Computer Engineering, Hanyang University, Seoul 133-791, Korea (Received 10 February 2009; accepted 7 April 2009)

X-ray diffraction patterns, scanning electron microscopy images, and transmission electron microscopy images showed that one-dimensional GaN nanorods with [0001]oriented single-crystalline wurtzite structures were grown on Al2O3 (0001) substrates by hydride vapor-phase epitaxy without a catalyst. The tip morphology of the GaN nanorods became flat with increasing temperature difference between the gas mixing and the substrate zones. The gas mixing temperature significantly affected the formation of the nanorods, and the substrate temperature influenced the morphology and the strain of the GaN nanorods near the GaN/Al2O3 heterointerface. The strain and the stress existing in the GaN layer near the heterointerface were decreased with increasing growth rate. The formation mechanisms of the GaN nanorods grown on the Al2O3 (0001) substrates are described on the basis of the experimental results.

I. INTRODUCTION

GaN-based materials have attracted a great deal of interest for optoelectronic devices operating in the visible-ultraviolet region of the spectrum1–3 due to their unique properties of direct and wide band gaps, large exciton binding energies, excellent chemical stabilities, and high temperature stabilities.4–7 Because bulk GaN substrates are not available yet, GaN materials are typically grown on heterosubstrates, such as c-Al2O3, 6H-SiC, and Si (111) substrates. It is not easy to obtain high-quality GaN materials because of the large difference in the lattice mismatch and the thermal expansion coefficient between the GaN layer and the foreign substrate. Many studies have been carried out to obtain high-quality GaN materials over the last several years.8,9 Among several methods for achieving a high-quality GaN, the most desirable way is the formation of single crystal GaN materials with one-dimensional (1D) nanostructures, such as nanowires and nanorods.10 Onedimensional nanostructural materials have become particularly attractive because of their potential applications in next-generation electronic and optoelectronic nanodevices operating at relatively low power consumption.11–14 a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0298

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http://journals.cambridge.org

J. Mater. Res., Vol. 24, No. 8, Aug 2009 Downloaded: 22 Mar 2015

Hydride vapor-phase epitaxy (HVPE) is a useful growth technique for growing thick GaN layers with high deposition rate and at a relatively low cost. Several growth techniques, such as metal organic chemical vapor deposition and molecular beam epitaxy,15,16 have been extensively used to grow high-quality 1D GaN single-crystalline nanostructures. However, the HVPE method is relatively little