TlGaAs and GaAs were grown by molecular-beam epitaxy at temperatures lower than 350degreesC and were investigated by means of X-ray diffraction as well as by secondary ion mass spectrometry combined with Rutherford backscattering spectrometry. At the growth temperature of 250degreesC, the incorporation of Tl into TlxGa1-xAs was limited to x = 1.2%, while the limit was extended beyond 2.8% at the growth temperature of 200degreesC. Taking into account the lattice expansion effect of As antisites, the expression of the lattice mismatch of TlxGa1-x-omegaAs1+omega to GaAs is deduced as a function of the Tl content x. (C) 2002 Elsevier Science B.V. All rights reserved.