GaAs devices have relatively high atomic numbers (Z=31, 33) and thus extend the X-ray absorption edge beyond that of Si (Z=14) devices. In this study, radiation detectors were processed on GaAs substrates with 110-130 mu m thick epitaxial absorption volume. Thick undoped and heavily doped p(+) epitaxial layers were grown using a custom-made horizontal Chloride Vapor Phase Epitaxy (CVPE) reactor, the growth rate of which was about 10 mu m/h. The GaAs p(+)/i/n(+) detectors were characterized by Capacitance Voltage (CV), Current Voltage (IV), Transient Current Technique (TCT) and Deep Level Transient Spectroscopy (DLTS) measurements. The full depletion voltage (V-fd) of the detectors with 110 mu m epi-layer thickness is in the range of 8-15 V and the leakage current density is about 10 nA/cm(2). The signal transit time determined by TCT is about 5 ns when the bias voltage is well above the value that produces the peak saturation drift velocity of electrons in GaAs at a given thickness. Numerical simulations with an appropriate defect model agree with the experimental results. (C) 2015 Elsevier B.V. All rights reserved.