The InAsSb epilayers with a cutoff wavelength of 11.5 mu m were successfully grown on highly lattice-mismatched semi-insulating (10 0) GaAs substrate by the modified liquid phase epitaxy (UPE) technique. Fourier transform infrared (FTIR) transmission spectrum revealed a strong band gap narrowing for this alloy. The electrical properties were investigated by the Van der Pauw measurements at 300 and 77 K. InAsSb epilayers showed high Hall mobilities being 11,800 cm(2)/V S at room temperature (RT). After an annealing treatment for 10 h, the electron mobility at 77 K were improved from 1730 cm(2)/V s Vs (prior to annealing) to 13,470 cm(2)/V S. Wet etching was used to display the surface etch pits prior to and after annealing treatment, showing that the mobility improvement was due to the reduction of the etch pits density. (C) 2009 Elsevier B.V. All rights reserved.