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RESEARCH PRODUCT

Raman study of strain in GaN/AlN quantum dot multilayered structures

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Raman spectroscopy has been used to investigate self-assembled stacks of GaN/AlN quantum dots with increasing number of periods. The E2H phonon modes associated to GaN and AlN are clearly resolved with visible excitation, and their energies allow the simultaneous monitoring of the dot and barrier strain states. The compression of the quantum dots is evidenced by a shift of the E2H phonon mode of circa 29 cm–1 to higher energies with respect to its relaxed value. The strain of the AlN spacer is found to be correlated to that of the dot, with an increase in its tensile component for the samples with fewer periods and a partial relaxation for samples over 50 periods. Additionally, resonant effects of the A1(LO) phonon mode have been investigated by tuning the excitation over a wide range in the ultra-violet region. A discussion of the strain distribution in quantum dots and spacers as a function of the number of periods is performed by means of a theoretical calculation based on the method of inclusions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)