Wide quantum wells, where the energy spacing between the first two energy levels is lower than the energy of the polar optical phonon, could represent the ideal condition to obtain a population inversion and the production of infrared lasers. On the other hand in these quantum wells the efficiency of carrier-carrier scattering is increasing with the width of the well and can produce a relatively quick relaxation of carriers in the first subband. In this work we present a detailed and systematic joint theoretical and experimental investigation considering different well width and carrier density and we conclude that in most cases the carrier-carrier scattering is sufficiently strong to forbid a significant population inversion.