Growth of GaInAs and A1InAs by molecular beam epitaxy on idium phosphide substrates is reported. Unintentionally doped, closely lattice matched GaInAs layers weren‐type with &mgr;300up to 8800 cm2 V−1 s−1andnas low as 1×1016cm−3whereas undoped A1InAs layers were typically high resistance. 2‐MeV Rutherford backscattering showed good GaInAs crystal quality although the A1InAs was somewhat disordered. Evidence for cation exchange at interfaces and surface accumulation of indium was evident from both RBS and sputter Auger profiles.Insitugrown A1 films on A1InAs showed an effective barrier height∼0.8 eV from 1/C2V s V curves, however attention to the forwardI‐Vcharacteristics indicated lower values. DLTS results indicate the GaInAs to be virtually trap‐free but that A1InAs has high deep level concentrations owing to low growth temperatures. Good photoluminescent efficiencies were demonstrated for GaInAs layers, however, poor results were obtained for A1InAs.