Surface radiation hard p(+)n Si pixel detectors are required for the science experiment at a synchrotron, and the major challenge is to improve the charge collection efficiency in the high-voltage X-ray-irradiated Si pixel detectors. Several experiments have been performed at DESY, Hamburg, Germany, within the AGIPD consortium on the test structures to extract the microscopic parameters of the X-ray-induced surface radiation damage in the detectors. The results on the microscopic parameters are fed into Cogenda Visual TCAD commercial simulation program to compare the experimental results and simulation data. A very good agreement has been recorded between the results and simulation data. In this paper, several surface radiation hard p(+)n Si pixel design options have been explored using a microscopic model for the improvement in the high-voltage stability of the detector and high-charge collection efficiency. A new intra-guard ring is incorporated in the design of the two adjacent p(+) pixels equipped with symmetric in and outward metal overhang extensions. The proposed surface radiation hard optimal design can enhance the electric field in the gutter region of the n-Si-bulk, a region which can have a very low electric field, which is just below the Si-SiO2 interface of the detectors, and this is the major concern for the charge loss in the X-ray-irradiated detectors. The results are discussed in detail using electric field distribution in the different designs of the pixel detectors for the different X-ray doses, and an optimized p(+)n Si pixel detector design with an intra-guard ring structure is proposed for the experiment.
