CARRIER-INDUCED LOCALIZATION IN IN-GA-AS IN-GA-AS-P SEPARATE-CONFINEMENT QUANTUM-WELL STRUCTURES/

We present a detailed analysis of carrier-induced modifications on the spatial band diagrams of In-Ga-As/In-Ga-As-P separate-confinement mul tiple-quantum-well structures and its consequences on optical properti es. In the high-carrier-density regime, we observe experimentally a se cond peak in the spectra of the optical gain. This can be understood b y a buildup of a space charge and band bending which is caused by a sp atial separation between electrons and holes due to the different dens ity of states of the conduction and valence bands. This band bending c auses a localization of barrier conduction-band states in the quantum- well region and an enhancement of the overlap integral of those states with quantized heavy-hole states giving rise to substantial modificat ions in the optical matrix elements. These modified matrix elements ar e the origin of the new class of optical transitions observed in the o ptical gain spectra.