The CEA is a major player in research into X-ray imagers for medical applications. For several years now, our laboratory at LITEN has been working in collaboration with LETI on a new generation of direct detectors based on halogenoplumbates perovskite photoconductors for applications in radiography, mammography and cardiac imaging. The laboratory has developed several processes for manufacturing thick films (>100µm) of perovskite semiconductors with state-of-the-art performances. However, they still need to be stabilized and improved to meet the stringent specifications of medical imaging. By analogy with other semiconductors (Si, Ge, CdTe, CZT, a-Se), it seems reasonable to assume that improving the performances of perovskite detectors will require advanced control of the bulk and surface properties of the semiconductor layer.
The candidate will be inspired by the developments of the perovskite community around high-purity single crystals for gamma detectors, and will transfer this know-how to the case of polycrystalline perovskite layers for X-rays. Initially, he will study the effects of unintentional extrinsic doping linked to the environment on the performance of X-ray detectors. Secondly, it will work to reduce the unintentional intrinsic doping by developing techniques for purifying precursor materials. At the same time, particular attention will be paid to the grain boundaries of polycrystalline layers and the feasibility of passivating surface defects using chemical treatments. The layers will then be tested in X-ray or gamma-ray detector devices. A thesis launched in parallel at LETI will characterize the density and nature of intrinsic carriers as a function of material and process conditions. Depending on the progress of the thesis, the possibility of intentionally doping the perovskite material could be explored. We hope that the results obtained as part of the thesis will enable us to improve the performance of X-ray detectors in order to meet medical imaging specifications, and to develop expertise in perovskite-based gamma detection. The work will be carried out in a highly collaborative environment involving laboratories from the CEA (LITEN, LETI, IRESNE), the CNRS (Institut Néel) and foreign laboratories. The PhD student will interact with several PhD students on a common topic.