Photoluminescence and X-Ray Diffraction Studies of the Diffusion Behaviour of Lattice Matched InGaAs/InP Heterostructures

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).

HRXRD data of samples annealed at various temperatures displayed contrasting states of strains. Detailed HRXRD measurements taken at various stages of annealing showed clearly that strains developed and grew with anneal time. They were initially characteristic of a higher diffusion rate for group V atoms, till a certain point at which group III diffusion became dominant. PL data supported that result, with a relative red-shift appearing at the onset of the prevalence of group III diffusion. Strain inversions and PL red-shifts occurred both at lower diffusion lengths when decreasing anneal temperatures, which was consistent with the miscibility gap growing within the InGaAsP quaternary diagram. This phenomenon explained the variety of results observed in the published literature and unified most of them. The HRXRD technique was also used to thoroughly characterise as-grown specimens.

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