The dynamics of excitons and trions in CdTe modulation-doped quantum wells are studied as a function of temperature by three-pulse four-wave mixing experiments. It is shown that trions are localized by interface roughness scattering and/or by the remote ionized donor potential at low temperature in the low-density regime. The diffusivity of excitons and trions increases with temperature but their mobilities are limited by acoustical phonon scattering, The coherence study reveals that the system is inhomogeneously broadened at low temperature and becomes nearly homogeneous as the temperature is increased.