Application of poly-Si/SiOx passivating contact in x-ray silicon pixel detector

Pixel x-ray detectors have been the working horse for the high resolution, high rate and high energy particle tracking for the past 20 years. In this paper, the (doped) poly-Si/SiOx is applied to heterojunction silicon pixel x-ray detectors. Ultrathin SiOx thin film of ~ 1.5 nm was prepared by wet chemical oxidation. Both P-type and N-type polycrystalline silicon (poly-Si) thin films were deposited on silicon oxide layer by APCVD to form the passivating contact on Si substrate. The influence of pixel size and the substrate thickness on the performance of pixel x-ray detectors was studied. The simulation results indicated that a thinner substrate was beneficial for the carrier transportation and collection. The experimental results showed that the leakage current turned large with increasing the pixel size. Whereas, the leakage current can be lowered by thinning the silicon substrate. Finally, the leakage current of 20 pA was achieved at room temperature for our 150 μm-large pixel x-ray detector and the energy resolution of 200 eV was obtained at 5.9 keV for the 305 μm-thick detector, which was better than that of detector on 525 μm substrate. The results suggested that good performance can be achieved for the pixel x-ray detector based on heterojunction on the thinned silicon substrate.