High performance X-ray detectors with sub-100eV energy resolution

软X射线检测应用广泛，从材料研究、医学成像到工业制造检测。该提案旨在开发一种新的软X射线（<20 keV）探测器，其具有比现有的冷却Ge和Si探测器更好的能量分辨率和灵敏度。这些新的X射线探测器将使用InAs制成，InAs是一种III-V族半导体材料，其具有上级Si的X射线探测特性的罕见组合，包括高X射线吸收系数，每个吸收光子产生的大量载流子，并且能够产生高增益而不引入过多噪声（最近在谢菲尔德发现）。这些InAs X射线雪崩光电二极管（APD）将被冷却以减少不需要的泄漏电流。我们的InAs APD有可能实现基本Fano因子限制的能量分辨率，而不是雪崩增益限制，从而改善了Si X射线APD的最佳数据。这可能是一种使技术能够获得高内部增益的好处，而不会导致显著的能量分辨率下降，这一直是X射线APD的主要缺点。它的衰减长度，即63%的X射线被吸收的距离，在5.9keV光子能量下比Si短6倍以上，在更高的能量下具有越来越大的优势。这使得更浅的InAs像素能够被制造，并且可能导致与数字X射线成像兼容的新一代大格式阵列。因此，本提案的最终目的是展示用于软X射线探测的具有高增益和优异能量分辨率的浅（<30微米）单像素InAs APD。这种新的能力可以支持下一代X射线检测的应用，如无损成像（材料研究中的故障分析和检查、电子元件/电路板检查和机械部件/组件）、医学成像（患者大面积成像，血管造影选择性显示体内血管），实时成像由于近年来谢菲尔德在InAs红外APD的晶片生长和器件制造方面取得了令人兴奋的进展，开发InAs X射线APD现在终于是可行的。尽管InAs X射线APD的开发面临着重大的不同挑战，但这两个项目的协同作用将加速其进展。研究人员拥有多年的APD经验，目前正在开发用于室温操作的AlGaAs X射线探测器，非常适合开展这项工作。除了演示高性能InAs X射线APD外，该项目还旨在开发一个X射线APD的设备模拟器，供其他X射线探测器研究人员使用。该模拟器具有预测能量分辨率极限的独特能力，同时考虑到雪崩增益过程的统计贡献。除了X射线APD模拟器，拟议的工作将建立晶片生长条件和设备制造程序适合于InAs X射线APD，并最终证明具有高增益和优良的能量分辨率的设备。

Soft X-ray detection is used in a wide range of applications ranging from material research, medical imaging, to industrial manufacturing inspection. This proposal aims to develop a new class of detectors for soft X-ray (<20keV) with potential to achieve better energy resolution and sensitivity than existing cooled Ge and Si detectors. These new X-ray detectors wil be made using InAs, a III-V semiconductor material which has a rare combination of properties for X-ray detection superior to Si, including high X-ray absorption coefficients, high number of carriers generated per absorbed photon, and ability to produce high gain without introducing excess noise (recently discovered at Sheffield).These InAs X-ray avalanche photodiodes (APDs) will be cooled to reduce unwanted leakage current. Our InAs APDs have the potential to achieve the fundamental Fano factor limited energy resolution rather than avalanche gain limited, thus improving on the best data from Si X-ray APDs. This could be the enabling technology to harvest the benefit of high internal gain without incurring significant energy resolution degradation, which has long been the main drawback of X-ray APDs. Its attenuation length, the distance by which the 63% of the X-ray is absorbed, is more than 6 times shorter than that of Si at 5.9keV photon energy, with increasing advantage at higher energies. This enables much shallower InAs pixel to be fabricated and could lead to a new generation of large format arrays that are compatible with digital X-ray imaging. Thus the ultimate aim of this proposal is to demonstrate shallow (<30micron) single-pixel InAs APDs with high gain and excellent energy resolution for soft X-ray detection. This new capability could underpin the next generation X-ray detection for applications such as non-destructive imaging (failure analysis and inspection in material research, electronic component/circuit board inspections and mechanical parts/assemblies), medical imaging (large area imaging of patients, angiography to selectively show blood vessels in the body), real-time imaging (to assist surgeries), and security screening of concealed objects through imaging.Developing InAs X-ray APDs is now finally feasible, owing to exciting developments in wafer growth and device fabrication at Sheffield in the recent years for InAs infrared APDs. Although there are significant different challenges in the development of InAs X-ray APDs, progress in both projects will be accelerated by the synergy. The investigator, who has years of experience with APDs and is currently developing AlGaAs X-ray detectors for room temperature operation, is well-placed to carry out the work. In addition to demonstration of high performance InAs X-ray APDs, this project aims to develop a device simulator of X-ray APDs which will be available to other X-ray detector researchers. This simulator has the unique ability to predict energy resolution limit, taking into account the statistical contribution of the avalanche gain process. In addition to the X-ray APD simulator, the proposed work will establish wafer growth conditions and device fabrication procedures appropriate for InAs X-ray APDs and eventually demonstrate devices with high gain and excellent energy resolution.