Using departure from stoichiometry for doping,p‐njunctions were prepared from CdxHg1−xTe alloys with 0.15 <x≤ 0.28, and their current‐voltage characteristics were measured at 77°K. The spectral study of these photovoltaic detectors operating at 77°K showed responses from 3 &mgr; up to 17.5 &mgr;. Detectivity measurements at the wavelengths of maximum response of these detectors yielded values at 77°K between 1 and 5 × 109cm‐W−1‐Hz1/2in the range 3 to 14 &mgr;. The speed of these detectors was measured to be <50 nsec, which was also confirmed by the observation of mode beats on the continuous output of a low‐power CO2laser at several frequencies up to 25 MHz.