On the diffusion of lattice matched InGaAs/InP microstructures

Coherent pseudomorphic structures that alternate nano-layers of contrasting strains have superior 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 miscibility gap properties of the InGaAsP system were characterised by newly associating Photoluminescence (PL) spectroscopy with High Resolution X-Ray Diffraction (HRXRD).

High temperature data (900oC) showed that lattice matched InGaAs/InP quantum wells interdiffused readily, with identical rates of diffusion for group III and V atoms. At 600oC, probably under the influence of the miscibility gap, HRXRD revealed strained layers in the annealed specimens. While strains were overall characteristic of larger diffusion lengths for group V atoms, PL data suggested that if group V atoms rate of diffusion was initially larger, group III interdiffusion later prevailed. This result suggested that the diffusion process is significantly altered by the presence of the miscibility gap. The strains evidenced were also consistent with a concentration dependant process. The technique appeared to provide a mean of surveying the miscibility gap, of monitoring diffusion and also characterising the formation of coherent strained layers.