Defects studies of BiI3-Polymer composites with carbon fillers to achieve better charge transportation for direct X-ray detectors

Wide bandgap heavy semiconductor materials capable of detecting X-rays at room-temperature without cryo-genic cooling have great advantages that include portability and wide-area deployment with major applications include medical imaging, spectroscopy, and astrophysics. BiI3 being a wide band gap material, is explored as a prospective material for X-ray and gamma ray detection. However, thick samples of Bismuth tri-iodide (BiI3) are more prone to defects, which trap the photo-generated charge carriers thereby limiting the charge collection efficiency. Here, we report the defects and charge transportation properties of BiI3-polymer (Polystyrene and Polymethyl-methacrylate) composite pellets of thickness 1.5 mm, upon irradiation with X-rays at tube voltage 60 kV. The defects in the samples have been studied using photoluminescence and the lifetime calculation has been done using Time Resolved Photoluminescence Spectroscopy. In order enhance the transport properties, defect engineering in the samples have been done by embedding carbon based conductive fillers into BiI3- polymer composites using hot compression method leading to decrease in the deep defect density. The mobility-lifetime product (mu-r) of the charge carriers in composite samples has been calculated to be 6.53 x 10-1 cm2/V, using modified Hetch equation which is enhanced from 10-4 cm2/V for pristine BiI3 and from 10-2 cm2/V for CdZnTe and perovskites-based detectors. Also, the charge collection has been achieved up to 90% at a bias of 0.8 V for BiI3-polystyrene/super carbon composite samples. The results indicate that defects have been mitigated in the stable BiI3-polymer/filler composite pellets, making them a promising material for room temperature X-ray detection and imaging applications.