H. Yamanishi

I. Yonenaga

K. Ueki

K. Wakita

S. Yamaguchi

T. Amano

T. Kuroda

National Institute for Fusion Science (NIFS-Repository)

§ 26. R&D of High Sensitive RadiationDetectorKuroda, T., Yamaguchi, S., Wakita, K. (ChubuUniv.)Amano, T. (Tokyo Univ. of Technol.)Yonenaga, I. (Tohoku Univ.)Ueki, K. (Natl. Maritime Res. Inst.)Yamanishi, H.The purpose of this study is to develope a radiationdetector of high sensitivity, and to apply that detector tothe LHD experiment. In addition, generally usedpossibility is pursued. In conventionally, radiationdetectors in which reverse bias is applied to a diodecomprising of semiconductors such as silicon orgermanium are used for detecting ionizing radiation. Sincethe energy of radiation is absorbed in a solid part whosedensity is high, it ·is expected that the sensitivity isessentially high. However, there is not amplification initself, and leak current is large. There are some limitationsof use, such as cooling it in liquid nitrogen temperature.For the above-mentioned situation, the element ofsemiconductor for light detection apparatus has beendeveloped recently, which has function of amplitude ownsignal. An example is raised in the following. That is anelement of a type called avalanche photo diode (APD). Inthe element, photoelectric effect is occurred as lightabsorption. This principle is the same as a normalsemiconductor detector for radiation. Therefore, it issuggested that APDs has sensitivity for ionizing radiationtheoretically. However, there have been few studies forthis application. In this .study, gallium/arsenic orindium/phosphorus are also assumed as element material.Because of high atomic number, absorption byphotoelectric effect becomes large in different order ofmagnitude comparing with silicon. Sensitivity of lowenergy X-ray will be improved as a result. In addition,sensitivity of high-energy gamma ray may become high.We have a plan of theoretical examination in theseelements.In the last year, it had been cleared up that APD has aperformance of radiation detection in high sensitivity.230In this year, a fabrication of Si-altemative semiconductorwas progressed.(1) Fabrication of a GaAs elementGaAs is suitable material in the gamma-rayspectroscopy which the band gap energy is wider incomparison with Si and Ge, and it works in roomtemperature. However, the non-dope layer of thicknessmore than 0.080 mm is necessary for gamma-ray detector,and super high purity is demanded. Super high purityGaAs liquid phase epitaxial growth (LPE) by a slide boatmethod was tried in an institution of Chubu University.The growth of crystal was conducted after heating a sourceplate in the circumstance of high purity hydrogen gas flow.The source plate was set at 800 degrees Celsius in 18hours for purification. After that, a basal plate was chargedin this circumstance for 90 min. The temperature wasreduced in a ratio of 1.0 degrees Celsius /min.. Therefore,the growth of crystal was started at 798 degrees Celsius.As a result, about 30mm growth layer was obtained.Carrier density 2*10 14cm-3 , mobility 50,000cm2/Vs wasgot by electric evaluation with a Hall effect. It was notremarkable high purity because of lack number of growth.We need to reach the performance, the carrier density lessthan 1013cm-3 , and the mobility more than 100,OOOcm2/Vs,for making a radiation detector.(2) Single crystal of GeSiA single crystal of GeSi (Ge 5%, Si 95%) was madein Tohoku University. It was processed into surface barriertype to be able to examine this as a radiation detector.This detection element is effective about 20mm insidediameter, thickness 7mm. The sensitivity characteristic forgamma rays will be examined under controled temperaturein order to reduce thermal noises.

R&D of High Sensitive Radiation Detector

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