We present a study of the room temperature electromodulation properties of CdHgTe heterostructures as a base component for a photorefractive device operating at 1.5 &mgr;m. We reach absorption modulation as high as 200&percent;, in the near-gap transparent region of the spectrum, by application of a reverse bias of the order of 100 kV/cm. We observe the transition from the Franz–Keldysh effect in 200 Å wide wells to the quantum confined Stark effect in 90 Å wells. The calculated diffraction efficiency in a suitable photorefractive device would be of the order of8×10−4in both cases. ©1997 American Institute of Physics.