Nanocrystalline Semiconductor Nuclear Radiation Detectors.

Abstract

The demand for precise and efficient nuclear radiation detection has significantly increased, especially in many scientific research fields as well as homeland security and medical imaging applications. The utilization of a quantum-dot-based semiconductor detector can, in principle, transform the capabilities of radiation detectors by yielding a high-performance detector via a low-cost solution-based fabrication modality. Nanocrystalline semiconductor (Nanocrystal, NC) materials exhibit exploitable properties, which arise due to the strong quantum confinement effect. If highly uniform multiplicities of excitons can be developed across macroscopic NC samples, then one can potentially quench the statistical counting noise associated with charge carrier creation in the bulk material. Based on the favorable features of NC materials for their application to the ionizing radiation detection, the NC approach, with a primary focus on the high atomic number and density materials (PbS, PbSe and CdTe), was investigated as a means to maximize the charge creation and minimize the uncertainty in that conversion. NC particles of different size and shape were synthesized by changing the reaction conditions, and their physical and opto-electric properties were investigated. Close-packed NC assemblies of cadmium and lead chalcogenides were formed by drop-, slide-, spin-casting or dip-coating NC dispersions on various metal contacts. Current-voltage (I-V) characteristics of each NC assembly were studied to evaluate its properties as an NC-assembly diode, as a function of the opto-electric properties of the NC particles, metal contacts, and the physiochemical property of the NC assembly. The responses of the NC assemblies toward radiation sources were studied via alpha particle impingement from an Am-241 source, and the highest energy-resolution samples exhibited a gamma-ray response that was comparable to existing semiconductor materials, including high-purity germanium and cadmium-zinc-telluride. The viability of using NC materials as a basis for the detection of ionizing radiation is assessed and empirical challenges are discussed. In short, this research focuses on fabricating nuclear radiation detectors out of nanocrystalline semiconductors via a solution-based approach. Various recipes and the subsequent electrical results for the NC assembly samples will be discussed, the main attention being paid to the enhancement of the charge carrier transport properties of the NC assembly.