We present the results of a study of the dynamics of trions and excitons in a CdTe modulationdoped quantum well as a function of temperature in the low-density regime. Using three-pulse four-wave mixing technique, we show that, at low temperature, these quasi-particles are inhomo-geneously broadened and localized due to disorder effects. At higher temperatures, trions and excitons are mobile and their homogeneous broadening is largely increased as a result of acoustic phonon scattering. Consistently, time-resolved luminescence measurements also reveal a free-particle character for trions at high temperatures.