This work reports a study of the passivation effects of different dielectric thin films deposited on monocrystalline CdTe/MgCdTe double heterostructures (DHs) using atomic layer deposition (ALD). Enhanced photoluminescence intensity was observed in all DHs with surface passivation, and increased photogenerated carrier lifetime was observed in DHs with HfO2, TiO2, Al2O3, and TiN passivated CdTe/MgCdTe DHs. These results have demonstrated effective suppression of the undesired surface recombination of CdTe/MgCdTe DHs by dielectric thin films deposited via ALD.