Annealing studies were performed on single hetero (SH) structures and multiple quantum well (MQW) structures of TlGaAs/GaAs grown by molecular-beam epitaxy (MBE) at a low growth temperature of 190 degrees C. X-ray diffraction (XRD) measurements on the SH structures revealed that the mole fraction of the antisite As in the low-temperature grown layers can be decreased to less than 0.1% by annealing at 450 degrees C for 30 min. Due to this annealing, however, decrease and inhomogeneity in Tl mole fraction were also caused. On the other hand, extending the total time of annealing at 400 degrees C to 16 h enabled us to decrease the antisite As mole fraction to about 0.1% without causing decrease and inhomogeneity in Tl mole fraction. It has also been confirmed that the well-defined MQW structures of TlGaAs/GaAs remain almost unchanged after annealing at 400 degrees C for 30 min. (c) 2006 Elsevier B.V. All rights reserved.