Temperature-dependent optical constant of an InGaAsP layer as determined from the reflectance spectrum

We demonstrate that the extinction coefficient and the refractive index, as well as the layer thickness, are obtained by comparing the simulation of the transfer matrix method with the reflectance spectrum of a 3-μm-thick InGaAsP layer on an InP substrate. The results clarify the complicated behavior of the optical constant near the energy gap. While the refractive index in the transparent region around the energy gap where active devices operate is approximated by a linear temperature dependence, complex behavior results from the singularity of the gap. We also find that the energy gap shrinkage with temperature follows the empirical law of Varshni.