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检测器（SDD）的研究与开发为了使SDD能够检测来自痕量污染物（如Cd）的高能x射线荧光，SDD的Si衬底厚度要求大于1mm。电阻率高于5 kΩcm的Si衬底是通过适当的反向偏置电压耗尽整个Si衬底所必需的，但电阻率高于5 kΩcm的Si衬底的SDD迄今尚未实现。我们讨论了如何利用电阻率大于5 kΩcm的Si衬底实现SDD的问题，并提出了一种利用电阻率大于5 kΩcm.2的Si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的深能级降低了x射线探测器的性能。由于表征低电阻率半导体深能级的典型方法（DLTS: deep level transient spectroscopy）不适用于高电阻率半导体和绝缘体，我们提出了用放电电流瞬态光谱（DCTS）测定高纯度半绝缘半导体（如4H-SiC）中深能级的密度和发射率。此外，从各发射速率的温度依赖性出发，确定了活化能（即各深能级能级）。由于这些x射线探测器有望在辐射环境中使用，我们利用霍尔效应测量研究了硅和碳化硅等半导体的辐射电阻。发现在高能电子的照射下，p型Si或p型SiC中的受体密度降低。另一方面，硅被发现比SiC更耐辐射。

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.