Amorphous and Nanocrystalline Semiconductors for Optoelectronic Applications: Photoconductors, Detectors and Sensors Based on a-Se Alloys and Optoelectronic Glasses

辐射探测和成像用光电材料的DG计划包括一项关于掺杂非晶态Se-As合金(a-Se：As)的主要研究，以及一项关于稀土掺杂玻璃和微晶玻璃(含纳米晶)的补充研究。与晶体半导体相比，a-Se合金有一个明显的优势，即它们可以方便地大面积制造，这使得它们在平板X射线图像探测器中得到了广泛的商业应用。长期目标是通过在材料和器件层面上的发现来扩展我们在掺杂a-Se合金半导体和器件方面的科学技术知识，并在基础层面上推进知识，从而增强我们的实力。下一代a-Se探测器的设计，特别是用于一般放射学、CT和断层合成的探测器，还需要广泛了解这三层中使用的光电导体的电学性质，例如漂移迁移率、载流子捕获和复合寿命、灵敏度、暗电流、过量噪声、热生成率、X射线诱导效应(如缺陷产生或损坏)和弛豫效应--这些合金是老化并表现出弛豫效应的玻璃。鉴于加拿大光源(CLS)的可用性，我们打算继续在我们的研究中使用同步加速器设施，并继续与CLS工作人员合作；也继续与我们的工业合作伙伴将结果与实际探测器联系起来。该研究计划将涵盖从目前到新的a-Se合金(掺杂)的光导体研究的方方面面，共同努力通过物理模型将探测器性能与基本半导体特性联系起来。它还将包括用于微束放射治疗的Sm3+掺杂玻璃和微晶玻璃，其中我们需要精确测量CLS BMIT线上微束中的剂量分布(峰值剂量为2-3kGy，宽度为20微米)。在这个DG计划中将有许多项目。典型例子：(A)研究了新掺杂的a-Se合金的光电性质随温度和电场的变化，从而得到具有较低暗电流和较高外场的增强p-i-n结构(较厚的i层)。(B)研究a-Se合金、MTF、DQE的光导随工作电场、温度、总剂量和剂量率的x射线能量依赖关系。(D)研究X射线照射对光导体性能的影响，从而对实际探测器的灵敏度和DQE的影响。(E)发现新的Sm掺杂光电玻璃(OGs)，这些玻璃与组织等效，可更好地监测MRT剂量分布并解决当前的问题(能源依赖性)。这项工作的影响是产生了关于具有新成分的掺杂a-Se合金的新知识，用于设计和开发下一代平板x射线探测器和用于高剂量剂量测量的新OEG。

The DG program on optoelectronic materials for radiation detection and imaging includes a major study on doped amorphous Se-As alloys (a-Se:As) and a complimentary study on rare-earth doped glasses and glass ceramics (containing nanocrystals). a-Se alloys have one clear distinct advantage over crystalline semiconductors that they can be conveniently fabricated over large areas, which has led to their extensive commercial use in flat panel x-ray image detectors. The long term objective is to build on strength by extending our scientific and technological knowledge on doped a-Se alloy based semiconductors and devices by discoveries at the material and device levels; and advancing knowledge at the fundamental level. The design of next generation a-Se detectors, in particular for use in general radiology, CT and tomosynthesis, also needs extensive knowledge of the electrical properties of the photoconductor used in the three layers, e.g. drift mobilities, carrier trapping and recombination lifetimes, sensitivity, dark current, excess noise, thermal generation rate, x-ray induced effects (such as defect creation or damage) and relaxation effects - these alloys are glasses that age and exhibit relaxation effects. Given the availability of the Canadian Light Source (CLS), we intend to continue to use of the synchrotron facility in our research and continue to collaborate with the CLS staff; and also continue with our industrial partner in relating results to practical detectors. The research program will encompass all aspects of photoconductor research from present to new a-Se alloys (doped) in a concerted effort to relate detector performance to fundamental semiconductor properties through physical models. It will also include Sm3+ doped glasses and glass ceramics for Microbeam Radiation Therapy in which we need to accurately measure the dose profile in the microbeam at the CLS BMIT line (peak dose 2 - 3 kGy with a width 20 um). There will be a number of projects within this DG program. Typical examples: (a) Study of optoelectronic properties of new doped a-Se alloys as a function of temperature and electric field toward enhanced p-i-n structures (thicker i-layer) with lower dark currents and higher applied fields. (b) Study of the x-ray energy dependence of photoconductivity of a-Se alloys, MTF, DQE as a function of operating field, temperature, total dose and dose rate. (d) Study of the effects of x-ray irradiation on the photoconductor properties and hence on the sensitivity and DQE of the actual detector. (e) Discovering new Sm-doped optoelectronic glasses (OEGs) that are tissue equivalent for better MRT dose distribution monitoring and addressing current problems (energy dependence). The impact of the work is the generation of new knowledge on doped a-Se alloys with new compositions for the design and development of next generation flat panel x-ray detectors and new OEGs for high-dose dosimetry.