The low-temperature growth of GaAs1-ySby with y = 0.4 and 0.85 has been reported recently along with characterization by X-ray diffraction, Hall, and current-voltage measurements. Here we extend the characterization by employing reflectance spectroscopy in the range 5-18 THz to confirm the compositions of the grown layers. In the course of this work we established for the first time that GaAs1-ySby may serve as an emitter of THz radiation under optical excitation by ultrashort pulses of near-infrared radiation in two distinct experimental arrangements: THz is generated when an electrical bias is applied through a simple electrode structure, attributed to a photoconductive effect; and THz is generated by the pristine layers themselves, attributed to a surface-field effect. In each case the THz emission is compared directly with that from low-temperature-grown GaAs. The results presented here are for as-grown material. Suitable annealing may improve the THz emission even further. (C) 2008 Elsevier Ltd. All rights reserved.