Scalable Manufacturing of Semiconducting Composite Devices for Ionizing Radiation Detection

Ionizing radiation detection including X-rays and Gamma rays have widely applications on clinic diagnostic, security check, industrial inspection, and cosmic exploration. The core idea of sensing these "invisible" photons is transferring the incident photons into readable signals by semiconductors. Semiconductor photoconductors and scintillators such as amorphous selenium (a-Se), cadmium telluride (CdTe), and thallium doped sodium iodide (NaI:Tl), etc. are predominantly used in commercial ionizing radiation detectors. These materials are generally obtained through a high temperature, vacuum, and time-consuming producing processes that limits the scalable-processibility and contributes to the relatively high cost of such detectors. In last decade, halide perovskite, a semiconducting compound (linear formula: ABX₃, where A=Cs or MA; B=Pb; X=Cl, Br, I) with astounding optoelectronic properties and low-cost nature, has attracted a lot of attentions. Such compounds can be dissolved into certain organic solvents and its precursors can further be crystallized into single crystals and polycrystal thin films. Most importantly, high atomic number elements such as cesium and lead contained make the perovskite a potential candidate for ionizing radiation detection purpose. Therefore, this dissertation focusses on the perovskite-based radiation detectors. To develop a new semiconductor detector which consisting combined properties of scalable-processibility and high detection sensitivity, the idea of produce perovskite-polymer semiconductor composites is firstly introduced in this dissertation. Pre-synthesized perovskite microcrystals and various polymers (polystyrene, polylactic acid, polystyrene-polyisoprene-polystyrene) are evenly mixed to fabricate the semiconducting composites. The positive impact of polymer-assisted composite on its mechanical properties can be summarized from the results. Subsequently, the scalable manufacturing processes, which include but not limited to hot-molding, melt-extruding, and 3D printing methods, are discovered to fabricate the customized-shape composite devices. On the other hand, improving the optoelectrical properties of perovskite-polymer composite is another crucial task. A unique method is demonstrated in this dissertation to modify perovskite microcrystals' surface for better dispersity of the perovskite microcrystals in composite. Followed by this, the perovskite/polymer ratios are also discussed for higher photon detection sensitivity. It is necessary to investigate charge carrier's behavior in our composites, which include but not limit to charge carriers' generation, separation, and transportation, within physical, chemical, and electrical interphases. Therefore, the mobility and lifetime of charge carriers (electrons and holes) are measured by Time-of Flight (TOF) technique. The mobility-lifetime product reaches to 10^(-4)~10^(-3) cm^(2)V^(-1), which can be compared with CdZnTe (CZT) based X-ray detectors. The Space Charge-Limited Current (SCLC) method and Many's equation was used to support the data from the TOF technique, these mobility and lifetime values extracted by different methods are showing strong consistency. Finally, as a proof of concept, a lead-free halide double perovskite, where one Ag⁺ and one Bi³⁺ replace two neighboring Pb²⁺ sites in the unit cells of haloplumbate perovskites without destroying the corner-sharing metal-halide octahedral networks of perovskite crystals, is used to fabricate the X-ray detection device to eliminate the toxicity of lead halide perovskite. The composite processing method introduced previously is also employed to halide double perovskite, for achieving solution-processed and flexible X-ray detectors and imagers with higher sensitivities.