InAs p-n diodes have been grown on GaAs and GaAs-coated Si substrates by molecular beam epitaxy. Transmission electron microscopy cross sections of the epilayers demonstrate a good structural quality. Photodiodes were obtained using a Be (p = 5 x 10(16) cm-3) and Si (n = 3 x 10(16) cm-3) doping scheme. The diodes exhibited 77 K zero-bias resistance area products of 2200 OMEGA cm2 for InAs/GaAs and 1500 OMEGA cm2 for InAs/GaAs/Si. The spectral response of the devices peaked at 2.95-mu-m with Johnson noise limited detectivities D* of 7.0 x 10(11) cm Hz1/2/W for InAs/GaAs and 5.8 x 10(11) cm Hz1/2/W for InAs/GaAs/Si. These results clearly demonstrate the feasibility of the monolithic integration of InAs infrared detectors and GaAs or Si read-out electronics.