Undoped InSb schottky detector for gamma ray measurements

Abstract

For measuring X-rays and gamma-rays with better energy resolution and higher efficiency than conventional semiconductor detectors such as Si and Ge detectors, we are studying InSb radiation detectors. Previously, we fabricated p-InSb Schottky type, pn-junction type detectors, and undoped InSb Schottky type detectors with an electrode of 3 mm in diameter, and measured alpha particles of 241 Am. For measuring gamma-rays, we fabricated undoped InSb Schottky type detectors with smaller electrode areas. Gamma-ray signals were clearly separated from the background, and differences between energy spectra of 241 Am and 133 Ba gamma-rays were observed.

Photon detection by a cryogenic InSb detector

“…In case of the energy of gamma rays being converted into electrons by photoelectric effect, the energy of photoelectrons is almost the same as that of primary gamma rays, i.e., 59 keV. The range of electrons with 59 keV in InSb substrate is estimated as nearly 20 m. 7 On the other hand, the depletion layer thickness of the undoped InSb detector without applying bias voltage was 9 m. 6 Most of the photoelectrons escaped from the depletion layer with depositing their energy partly. For the measurement of a photopeak, the thickness of the depletion layer should be increased.…”

“…This undoped wafer was n-type by the polarity of preamplifier output pulses in the alpha particle measurements. 6 The wafer was cut to the dimensions of nearly 5 mmϫ 7 mm. Both sides of the InSb substrate were etched using a mixture of nitric and lactic acids (1:10) for 5 min.…”