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Photoluminescence and Raman analysis of strain and composition in InGaAs/AlGaAs pseudomorphic heterostructures

Photoluminescence and Raman spectroscopy have been used to determine composition and strain in pseudomorphic InxGa1-xAs/AlxGa1-yAs quantum wells. Series of MBE-grown samples, comprising bulk-relaxed InxGa1-xAs reference layers and InxGa1-xAs/AlyGa1-yAs quantum wells of different thicknesses, were considered. Photoluminescence transitions in the strained structures were analysed using a semiempirical model including strain and composition effects in the InxGa1-xAs well. The GaAs-like longitudinal optical LO phonon Raman shift allowed an independent strain estimation. The agreement between photoluminescence and Raman results confirms the assumption that there is no relaxation in the wells. The effects of uncertainties in the stress deformation potentials and phonon coefficients on strain determination have been discussed. The authors' results show that photoluminescence is an adequate tool to characterize InGaAs strained layers.