Barrier-induced carrier localization effects in ordered/disordered/ordered quaternary quantum wells grown on GaAs substrates

Optical and micro-structural properties of ordered/disordered/ordered InGaAsP quantum wells grown on GaAs substrates were investigated by photoluminescence spectroscopy, high-resolution transmission electron microscopy and selective area diffraction. Strong evidence of carrier localization effects was obtained from low temperature photoluminescence experiments. Photoluminescence spectra of thinner quantum wells were dominated by a broad emission band located at energies below the bandgap of the well material. The energy peak position of this emission varied considerably with the laser excitation power. Carrier localization was attributed to potential fluctuations in the barrier and well layers, as a result of two coexisting effects: Spontaneously atomic ordering and, in a minor degree, alloy inhomogeneities. We show that a reduction of the ordering degree in the bottom barrier layer resulted in a considerable decrease of localization effects in quaternary quantum well heterostructures.