GaPAsSb type-I quantum wells and symmetric InGaAs/GaPAsSb/InGaAs type-II quantum wells are proposed as long wavelength active layers for GaAs based optoelectronic devices. Room temperature photoluminescence from 1.3 to 1.5 mu m is observed from the type-II quantum wells, while low temperature photoluminescence at 1.25 mu m is observed from type-I quantum wells. A reflection high-energy electron diffraction peak that is extended pal-allel to the surface, while its width is perpendicular to the surface is narrow, suggests that spontaneous lateral composition modulation occurs in the GaPAsSb layers.