Using departure from stoichiometry, p-n junctions were prepared in Cd x Hg 1-x Te with x \simeq 0.20 for the study of photovoltaic detection at 10.6 μ. In the final photodiodes, with sensitive areas between 4 \times 10^{-4} and 10-3cm2, values such as 10^{5} \Omega and 8 pF have been observed at -0.1 V reverse bias for the shunt resistance and capacitance at 77°K. The CO 2 laser detection characteristics were investigated, leading to 1010 \leq 5 \times 10^{10} cm W-1Hz1/2, a frequency response flat up to 1 GHz, a heterodyne noise equivalent power (NEP) = 8 \times 10^{-20} W/Hz with l-mW local oscillator power. Studies as a function of the temperature indicated that substantial sensitivity can be obtained up to 135°K.