Lateral composition modulation in InGaAsP strained layers and quantum wells grown on (100) InP by gas source molecular beam epitaxy

Lateral composition modulation (LCM) in InGaAsP layers (1500 Angstrom) and quantum wells (50 Angstrom) grown on (100) InP substrates by gas source molecular beam epitaxy were studied over a wide alloy range. Layers with lattice mismatches of -0.5% (compression), 0% (lattice-matched) and +0.5% (tension) were studied using photoluminescence, transmission electron microscopy and X-ray diffraction. Greater compositional fluctuations were observed for tensile material, compared with lattice-matched or compressively strained material. This is consistent with tensile material having nominal compositions that lie deeper within the calculated bulk spinodal isotherm. However, differences between the observed LCM structure and that predicted by bulk models, and the influence of growth conditions and lattice mismatch strain on the compositional fluctuations, suggest the need for a surface spinodal model.