Characterization of interdiffusion around miscibility gap of lattice matched InGaAs/InP quantum wells by high resolution x-ray diffraction

Coherent pseudomorphic structures that alternate nano-layers of contrasting strains have higher strength. Their long term stability to thermal diffusion would be at the heart of a new design concept for structural materials destined to very high temperature applications. The project aimed at exploring the prospect of inhibiting diffusion between compositionally dissimilar coherent layers by using the properties of a miscibility gap. Model crystalline heterostructures of the technologically important InGaAsP semiconductor system were grown by epitaxy. Thermal interdiffusion in lattice matched InGaAs/InP Quantum Wells (QW) and the miscibility gap properties of the InGaAsP system were characterised by newly associating Photoluminescence (PL) spectroscopy with High Resolution X-Ray Diffraction (HRXRD).

The modelling of HRXRD rocking curves was pushed further to extract detailed information on the strains and compositions generated by interdiffusion of lattice matched InGaAs/InP QW specimens annealed at 800oC. A novel methodology simplified the curve fitting procedure to first extract strain information from the strain sensitive 004 rocking curves. The strain information was then used to constrain the curve fit of composition sensitive 002 rocking curves, and extract compositional information. Results clearly showed that under the influence of the miscibility gap, group V atoms initially diffuse at a higher rate, and then group III atoms diffusion prevails. The compositional information appeared to describe a diffusion path around the miscibility gap in the InGaAsP quaternary diagram, thus providing the first published experimental evidence of the miscibility gap contour.

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