Near-band-gap absorption of InGaAsP at 1.3 μm wavelength

InGaAsP, adapted in its composition for a band gap equivalent to a wavelength of 1.3 μm and lattice matched to InP, is grown by liquid-phase epitaxy. Transmission and reflectance measurements in the vicinity of the band gap are made, from which the refractive index of both InP and the quaternary compound are derived. Also the optical absorption coefficient α of the quaternary compound is obtained. Above the band gap, α can be fitted to the model of direct band-to-band transitions, allowing the precise determination of the band-gap energy. Below the band gap, α follows an exponential dependence on photon energy. Using material parameters for the quaternary compound, the role of phonon-assisted transitions is discussed in this spectral range. (author)