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）生长的厚CdTe薄膜研制大面积高性能辐射成像探测器。1. CdTe/n^<+->GaAs异质结二极管探测器的研制采用MOVPE法在n^<+->GaAs衬底上生长厚p-CdTe层，制备了异质结二极管探测器。首次证实了该探测器对59 keV入射Am源γ射线的探测和能量分辨能力。2.发展了MOVPE法在Si衬底上直接生长CdTe单晶层的技术，首次实现了在Si衬底上直接生长CdTe单晶层。作为在Si上生长CdTe之前的预处理，Si衬底与GaAs片一起在氢气环境中退火。辐射探测器所必需的高质量CdTe厚层的生长也通过使用以下生长技术来实现。在Si衬底上生长CdTe薄层后，释放生长层中的残余应力，在其上生长厚的CdTe层。3. CdTe/n^<+->Si异质结二极管探测器的研制在上述（1）和（2）结果的基础上，直接在n^<+->Si衬底上生长厚的p-CdTe层，制成了异质结二极管探测器。探测器被证实具有良好的电气特性。通过以上研究，建立了实现目标探测器所必需的基本技术。

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.