We have characterized the performance of soft-X-ray detectors fabricated with undoped and B-doped homoepitaxial diamond layers of high quality which were grown on a commercially available type Ib (1 0 0) substrate by means of a high-power microwave-plasma chemical-vapor-deposition (CVD) method. The signal currents of the diamond-based detectors with thin TiN electrodes formed vertically (along the homoepitaxial growth direction) were measured at room temperature as a function of the applied voltage, V-a, for irradiations of 500-1200 eV soft-X-ray beams ranging from approximate to 6 x 10(9) to approximate to 1 x 10(11) photons/s. The deduced apparent quantum efficiencies increased with the increasing V-a and reached to 2.5 x 10(3) at V-a = 60 V. As expected from the device structure, the detector performance depended only very slightly on the applied magnetic field up to 10 T. The excellently high sensitivities attained for soft-X-ray photons are discussed in relation to carrier amplification mechanisms which invested the above diamond detectors. (C) 2008 Elsevier B. V. All rights reserved.