Abstract
Phonon frequencies of a high-quality AlN layer coherently grown on a 6H-SiC (0001) substrate are investigated by Raman scattering. Owing to the largest strain in our coherent AlN layer among heteroepitaxially grown AlN layers ever reported, phonon frequencies of the E2 (low), E2 (high), and A1 (LO) modes are considerably shifted to 244.5 (−3.3, compared with bulk AlN), 672.1 (+16.3), and 899 (+11)cm−1, respectively. Full widths at half maximum of the phonon modes in the coherent AlN are almost equal to those of high-quality bulk AlN, clearly indicating its high crystalline quality and uniform strain. We discuss accuracy of phonon deformation potentials reported by several other groups thorough comparing our experimental results.
Highlights
Raman scattering is a powerful tool to investigate strain states since Raman spectra can be obtained without special sample preparation.[1,2]
Study of the phonon deformation potentials (PDPs) of aluminum nitride (AlN) is still immature and there is a great discrepancy between reports.[8,9,10,11,12,13,14]
We have focused on AlN growth on SiC substrates by rf-plasma-assisted molecular beam epitaxy
Summary
Raman scattering is a powerful tool to investigate strain states since Raman spectra can be obtained without special sample preparation.[1,2] By focusing incident light through optical lenses, high spatial resolution (∼1 μm) can be achieved.[3,4] To obtain strain states from Raman spectra, phonon deformation potentials (PDPs) are needed. Phonon frequencies of a highly strained AlN layer coherently grown on 6H-SiC (0001) Suda Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan (Received 6 December 2016; accepted 9 January 2017; published online 18 January 2017)
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