3D semiconductor radiation detectors for medical imaging: Simulation and design

In conventional planar detection structures, photon absorption efficiency is limited by the thickness of the detector, which is itself limited by charge transport properties in the chosen material. Therefore a trade-off must be found between photons absorption efficiency and charge collection efficiency. To overcome this compromise, alternative detector architecture has been proposed [1], where charge collection is realized perpendicularly to the photon absorption plane. The volume of the detector is micro-structured with an array of columnar electrodes (alternatively anodes and cathodes) which penetrate through the whole bulk. Thanks to this new 3D architecture of the detectors, and as long as electrodes are sufficiently close, various semiconductor materials can be considered for room temperature use. CdTe and GaAs 3D detectors have been simulated thanks to a complete model coupling Monte-Carlo modeling of interaction of X- and γ-rays with matter (with PENELOPE, [2]) and computation of Charge Induction Efficiency (CIE) with finite elements method. Planar structures of the same material have also been simulated for comparison purposes. CdTe and GaAs single crystal detectors with an electrode pitch of 7μm have demonstrated spectrometric efficiency, i.e. discrimination of the energies of incident rays in the considered radiation energy range (typically 10μ160 keV for medical applications). Detectors with an electrode pitch of 350μm allowed the counting of photons arriving on the detector, without energy discrimination, which is suitable for X-ray imaging in medical applications.