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Depth resolved studies of indium content and strain in InGaN layers

Pereira, S.M.D.S. and Correia, M.R. and Ferreira Pereira Lopes, E.M. and O'Donnell, K.P. and Trager-Cowan, C. and Sweeney, F. and Alves, E. and Sequeira, A.D. and Franco, N. and Watson, I.M. (2001) Depth resolved studies of indium content and strain in InGaN layers. Physica Status Solidi B, 228 (1). pp. 59-64. ISSN 0370-1972

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Abstract

A depth resolved study of optical and structural properties in wurtzite InGaN/GaN bilayers grown by MOCVD on sapphire substrates is reported. Depth resolved cathodoluminescence (CL), Rutherford backscattering spectrometry (RBS) and high resolution X-ray diffraction (HRXRD) were used to gain an insight into the composition and strain depth profiles. It is found that both quantities can vary considerably over depth. Two representative samples are discussed. The first shows a CL peak shift to the blue when the electron beam energy is increased. Such behaviour conforms to the In/Ga profile derived from RBS, where a linear decrease of the In mole fraction from the near surface (0.20) down to the near GaN/InGaN interface (0.14) region was found. The other sample discussed shows no depth variations of composition. However, the strain changes from nearly pseudomorphic, close the GaN interface, to an almost relaxed state close to the surface. This discrete variation of strain over depth, originates a double XRD and CL peak related to InGaN.