Abstract
We report observation of catalyst-free hydride vapor phase epitaxy growth of InN nanorods. Characterization of the nanorods with transmission electron microscopy, and X-ray diffraction show that the nanorods are stoichiometric 2H–InN single crystals growing in the [0001] orientation. The InN rods are uniform, showing very little variation in both diameter and length. Surprisingly, the rods show clear epitaxial relations with thec-plane sapphire substrate, despite about 29% of lattice mismatch. Comparing catalyst-free with Ni-catalyzed growth, the only difference observed is in the density of nucleation sites, suggesting that Ni does not work like the typical vapor–liquid–solid catalyst, but rather functions as a nucleation promoter by catalyzing the decomposition of ammonia. No conclusive photoluminescence was observed from single nanorods, while integrating over a large area showed weak wide emissions centered at 0.78 and at 1.9 eV.
Highlights
InN marks the lower bandgap limit achievable within the group III-nitride semiconductor family
We report an observation of catalyst-free epitaxial growth of remarkably size-uniform and vertically-aligned InN nanorods on c-plane sapphire
Samples deposited with Ni catalyst produced the same size, length, and shape of rods, except for a much higher nucleation density of 6–8 rods per lm2 (Fig. 2, bottom panel), effectively fusing the nanorods into a continuous layer
Summary
InN marks the lower bandgap limit achievable within the group III-nitride semiconductor family. Growth with Au catalyst has been reported [3], but due to its relatively low efficiency, it typically requires large flow of ammonia. We report an observation of catalyst-free epitaxial growth of remarkably size-uniform and vertically-aligned InN nanorods on c-plane sapphire. We compare this growth to Ni catalyzed growth under the same conditions and suggest that a growth mechanism other than vapor–liquid–solid (VLS) may be responsible for the observed uniformity. Ammonia is delivered to the growth zone via separate 10 mm diameter quartz tube, and the InCl gas reacts with ammonia to form InN. The emitted luminescence was dispersed by a monochromator, filtered, and sensed using a Si CCD camera
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