Structural properties of 10 μm thick InN grown on sapphire (0001)
Introduction
It is only recently that InN single crystals of decent structural quality have been heteroepitaxially grown by a limited number of research groups worldwide. Most of the InN structural investigations have been based on x-ray diffraction measurements and just a few on transmission electron microscopy [1], [2], [3]. As has been shown for GaN [4], [5], [6], a more complete analysis can be obtained using both of the above techniques and comparing their results.
In this paper, we focused our studies on the structural quality of InN (0001) heteroepitaxially grown on Al2O3 by molecular beam epitaxy. We used both transmission electron microscopy (TEM) and high resolution x-ray diffraction (HR-XRD), in order to investigate the structural properties of InN and determine the density of threading dislocations (TDs). In the case of TEM, TD density was directly measured, while in the case of HR-XRD it was calculated through the peak broadening. Comparing the results of TEM with those of HR-XRD, conclusions about the spatial distribution of the pure-edge TDs in InN were drawn. Besides the comparison between TEM and HR-XRD as structural characterization tools, we also investigated the evolution of TDs along the [0001] growth direction. For the purposes of this work, we examined a sample consisting of a 10 μm thick InN epilayer grown on Al2O3 using thin intermediate layers of AlN and GaN.
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Experimental details
The sample we study in this work was grown on -plane Al2O3 substrate by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). In order to ensure the III-polarity of the epilayers, the substrate was initially nitridated at 300 ∘C and subsequently a 65 nm thick AlN layer was grown at 800 ∘C, followed by a 160 nm thick GaN layer at 700 ∘C. Finally, a 10 μm thick InN epilayer was grown at 400 ∘C using equal indium and active nitrogen fluxes. The growth of InN was performed in a single
Structural characterization by TEM
In the first part of this work, the structural quality of InN is being investigated by TEM. An XTEM micrograph of the film is shown in Fig. 1. The AlN interlayer, about 65 nm in thickness, can be also clearly depicted between the 160 nm thick GaN layer and the sapphire substrate. InN follows a compact growth mode, having an epitaxial orientation relationship of as shown in the corresponding selected
Conclusions
The structural properties of a 10 μm thick InN heteroepitaxial layer grown on Al2O3 by RF-MBE were investigated using TEM and HR-XRD. Threading dislocations of edge, screw and mixed character were the dominant defects in InN. The densities of pure edge and mixed type dislocations were found to decrease along the [0001] growth direction, while that of pure screw dislocations was found to remain constant. Comparing TEM with HR-XRD results, it was suggested that the edge dislocation distribution
Acknowledgements
The support of EU by the Marie Curie RTN program MRTN-CT-2004-005583 (PARSEM) is gratefully acknowledged. One of the authors (E. D.) acknowledges support by a PENED 01ED481 Ph. D. Scholarship. This work was also supported by MNiI (Polish Ministry of Science and Informatisation) grant no. 4T07A-01026.
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