High quality CdTe and its application to radiation detectors

CdTe crystal growth by the travelling heater method and the characteristics of its radiation detectors are described. A CdTe polycrystalline ingot is synthesized from purified 99.99999% Cd and Te metals and crystals of 32 mm in diameter are grown at temperaturesof 700°C–900°C with a growth speed of 2–5 mm per day. A high resistivity of more than 10 9 Ω cm is obtained at a Cl concentration of 1.5 ppm with electron and hole lifetimes of 1.0 and 0.5 μs respectively. The pulse count mode detectors are fabricated using wafers cut from the ingots. For practical application to medical diagnostics, 90-element array detectors with an element size of 1.8 mm × 2 mm × 1.2 mm are developed. The averaged FWHM is 4.0 keV and the count rate variation is less than 4% for a 60 keV γ-ray source. For dosimetry use, detectors as large as 10 mm × 10 mm × 2 mm and 25 mm diameter × 2 mm thickness volumes are fabricated. Environmental and high temperature acceleration tests have been systematically conducted. Mean time to failure is estimated to be 10 9 h at 25°C.