InAs0.05Sb0.95 photoconductive infra-red detectors have been grown by molecular beam epitaxy in recessed Si wells. The embedded devices exhibited a voltage responsivity of 420 V/W at 77 K and 300 meV photon energy with a load resistor of 100 Ω and a bias voltage of 1.5 V. © 1990, The Institution of Electrical Engineers. All rights reserved.