Investigation of high energy X-ray detectors to detect a trace of pollutant capable of operating at room temperature

1.用于高能X射线荧光的高灵敏度硅漂移探测器(SDD)的研制为了使SDD能够从Cd等痕量污染物中探测到高能X射线荧光，SDD用硅衬底的厚度要求大于1 mm。为了通过适当的反向偏置电压来耗尽整个硅衬底，电阻率大于5kΩcm的硅衬底是必要的，但电阻率大于5kΩcm的硅衬底的SDD尚未实现。我们讨论了如何实现电阻率高于5kΩcm的硅衬底的SDD，并提出了一种使用电阻率高于5kΩcm的硅衬底实现SDD的新结构。半绝缘半导体室温工作X射线探测器的研究半导体中的深能级降低了X射线探测器的性能。由于用于表征低阻半导体深能级的典型方法(DLTS：深能级瞬变光谱)不适用于高阻半导体和绝缘体，我们用我们提出的放电电流瞬变光谱(DCTS)测量了4H-SiC等高纯半绝缘半导体的深能级密度和发射率。根据各发射率随温度的变化关系，确定了激活能(即各深能级的能级)。用于X射线探测器的半导体抗辐射性能的研究由于这些X射线探测器有望在辐射环境中使用，我们用霍尔效应测量方法研究了半导体如硅和碳化硅的抗辐射性能。高能电子辐照降低了p型硅和p型碳化硅中的受主密度。另一方面，人们发现硅比碳化硅具有更强的抗辐射能力。

1. Research and development of highly-sensitive silicon drift detector (SDD) for high-energy X-ray fluorescenceIn order for SDD to detect high-energy X-ray fluorescence from a trace of pollutants such as Cd, the thickness of Si substrate for SDD required to be thicker than 1 mm. The Si substrate with resistivity higher than 5 kΩcm is necessary to deplete the whole Si substrate by an appropriate reverse bias voltage, but SDD with the Si substrate with resistivity higher than 5 kΩcm has not been materialized to date.We have discussed the problem of how to materialize the SDD with the Si substrate with resistivity higher than 5 kΩcm, and have proposed a new structure of SDD using Si substrate with resistivity higher than 5 kΩcm.2. Research of room-temperature-operating X-ray detector made of semi-insulating semiconductorDeep levels in semiconductors degrade the performance of X-ray detector. Because the typical method (DLTS: deep level transient spectroscopy) for characterization of deep levels in low-resistivity semiconductors is not suitable for high-resistivity semiconductors and insulators, we have determined the densities and emission rates of deep levels in high-purity semi-insulating semiconductors such as 4H-SiC by discharge current transient spectroscopy (DCTS) that we have proposed. From the temperature dependence of each emission rate, moreover, the activation energy (i.e., energy level of each deep level) has been determined.3. Study of radiation resistance of semiconductor for X-ray detectorSince these X-ray detectors are expected to be used in radiation environments, we have investigated the radiation resistance of semiconductors such as Si and SiC using Hall-effect measurements. The density of acceptors in p-type Si or p-type SiC is found to be decreased by irradiation of high-energy electrons. On the other hand, Si is found to be radiation-resistant more than SiC.