Development of Large Area and High Performance Radiation Imaging Detectors for Medical Use

研究了利用金属有机气相外延（MOVPE）生长的CdTe厚层开发大面积高性能辐射成像探测器。取得了以下3项主要成果：1.提高工作效率；CdTe/n^<+->GaAs异质结二极管探测器的研制。采用MOVPE在n^<+->GaAs衬底上生长p-CdTe厚层制备异质结二极管探测器。首次证实了对来自Am源的59 keV入射伽马射线的探测和能量分辨能力。对探测器的结构进行了优化。MOVPE在Si衬底上直接生长CdTe薄膜技术的发展。首次实现了用MOVPE直接在Si衬底上生长单晶CdTe层。作为CdTe在Si上生长前的预处理，用GaAs片在氢环境中对Si衬底进行了退火。高质量的碲化镉厚层的生长，这是必要的辐射探测器，也实现了使用以下生长技术。在Si衬底上生长CdTe薄层后，生长层中的残余应力得到松弛，并在其上生长出较厚的CdTe层。CdTe/n^<+->Si异质结二极管探测器的研制。在上述1和2的基础上，利用直接生长在n^<+->Si衬底上的厚p-CdTe层制备了异质结二极管探测器。这些探测器被证实具有良好的电气特性。对探测器性能的改进进行了研究。在上述研究过程中，建立了实现目标探测器所必须的基本技术。

Development of large area and high performance radiation imaging detectors using thick CdTe layers grown by Metalorganic vapor phase epitaxy (MOVPE) has been studied. The following 3 major achievements were obtained.1.Development of CdTe/n^<+->GaAs heterojunction diode detectors.Heterojunction diode detectors were fabricated using thick p-CdTe layers grown on n^<+->GaAs substrates by MOVPE. Detection and energy discrimination capabilities for the incident gamma ray of 59 keV from Am source were confirmed for the first time. Optimization of the detector structure was also carried out.2.Development of direct growth technique of CdTe lavers on Si substrates by MOVPE.Growth of single crystal CdTe layers directly on Si substrates by MOVPE was achieved for the first time. As a pretreatment before the CdTe growth on Si, the Si substrates were annealed with GaAs pieces in the hydrogen environment. Growth of high quality CdTe thick layers, which were necessary for radiation detectors, was also achieved by using the following growth technique. After the growth of thin CdTe layers on Si substrates, residual stress in the grown layers were relaxed, and thick CdTe layers were grown on them.3.Development of CdTe/n^<+->Si heterojunction diode detectors.On the basis of results obtained in 1 and 2 above, heterojunction diode detectors using thick p-CdTe layers grown directly on n^<+->Si substrates were fabricated. The detectors were confirmed to have good electrical characteristics. Improvements of the detector performance were also studied.Throughout the above studies, fundamental techniques which were inevitable to realize the purposed detectors were established.