A new type of radiation detector, a p-type modified electrode germanium diode, is presented. It is shown that the prototype displays, for the first time, a combination of features (mass, energy threshold and background expectation) required for a measurement of coherent neutrino-nucleus scattering in a nuclear reactor experiment. First results are presented from its calibration using sub-kiloelectronvolt nuclear recoils similar to those expected from reactor antineutrinos or light WIMPs (weakly interacting massive particles) beyond the reach of present detectors. The device hybridizes the mass and energy resolution of a conventional HPGe coaxial gamma spectrometer with the low electronic noise and threshold of a small x-ray semiconductor detector, also displaying an intrinsic ability to distinguish multiple-site from single-site particle interactions. The present performance of the prototype and possible further improvements are discussed, as well as other applications for this new type of device in neutrino and astroparticle physics (double-beta decay, neutrino magnetic moment and novel WIMP searches). © IOP Publishing Ltd.