Effect of Thermal Annealing in Ammonia on the Properties of InGaN Nanowires with Different Indium Concentrations

• Published in: Journal of physical chemistry. C 2013-02, Vol.117 (7), p.3627-3634
• Main Authors: Hahn, Christopher, Cordones, Amy A, Andrews, Sean C, Gao, Hanwei, Fu, Anthony, Leone, Stephen R, Yang, Peidong
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electric Phenomena; Exact sciences and technology; MATERIALS SCIENCE; Nanocrystals and nanoparticles; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures; Physics
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp311685x

The utility of an annealing procedure in ammonia ambient is investigated for improving the optical characteristics of In x Ga1–x N nanowires (0.07 ≤ x ≤ 0.42) grown on c-Al2O3 using a halide chemical vapor deposition method. Morphological studies using scanning electron microscopy confirm that the nanowire morphology is retained after annealing in ammonia at temperatures up to 800 °C. However, significant indium etching and composition inhomogeneities are observed for higher indium composition nanowires (x = 0.28, 0.42), as measured by energy-dispersive X-ray spectroscopy and Z-contrast scanning transmission electron microscopy. Structural analyses, using X-ray diffraction and high-resolution transmission electron microscopy, indicate that this is a result of the greater thermal instability of higher indium composition nanowires. The effect of these structural changes on the optical quality of InGaN nanowires is examined using steady-state and time-resolved photoluminescence measurements. Annealing in ammonia enhances the integrated photoluminescence intensity of In x Ga1–x N nanowires by up to a factor of 4.11 ± 0.03 (for x = 0.42) by increasing the rate of radiative recombination. Fitting of photoluminescence decay curves to a Kohlrausch stretched exponential indicates that this increase is directly related to a larger distribution of recombination rates from composition inhomogeneities caused by annealing. The results demonstrate the role of thermal instability on the improved optical properties of InGaN nanowires annealed in ammonia.