Anomalous behavior of phase separation of InGaAsP on GaAs substrates grown by MOVPE

Immiscibility in InGaAsP on GaAs substrates grown by metalorganic vapor phase epitaxy (MOVPE) has been investigated. Epitaxial layers of InGaAsP over a wide compositional range were grown on (100) exact and 10° off toward 〈1 1 1〉 A GaAs substrates at the same time under growth temperatures of 630 and 690 °C. We examined the immiscibility by using measurements of surface roughness and optical characteristics, and revealed that the calculation based on the strictly regular solution model agreed very well to the immiscibility of InGaAsP grown on 10° off substrates at 690 °C. Furthermore, as for the samples grown at 690 °C on (100) exact substrates or grown at 630 °C, the phase separation was suppressed even in the unstable compositional region, especially in the compositions close to InGaP. This phenomenon is due to influence of the surface reconstruction of InGaAsP layers.