MIS tunnel diode as a low energy X-ray and gamma-ray detector

Highly perfect n-type cadmium telluride single crystals have been used to fabricate semiconductor detectors for X-ray and low energy gamma-ray spectrometry at room temperature. The detectors are of MIS tunnel diode type. Between the metal (M) and the semiconducting CdTe crystals (S) there is a thin insulator (D) with a critical value of thickness. The mechanism for a current condition is tunneling through the insulator. Our studies by SIMS and ellipsometry show that there is a nonstoichiometric region between the insulator and the semiconductor and in the insulator with thickness below 30 A. The effect of the nonstoichiometry in the MIS structure upon spectrometric performance of the detector has been analyzed. A considerable improvement of the energy resolution for full energy peak can be achieved by appropriate interfaces of the MIS tunnel detectors. The Np - Lα (13.9 keV), Np -Lβ (17.7 keV) and Np -Lγ (20.8 keV) X-ray are clearly resolved. The spectrum of the characteristic X-ray from 55Fe source (5.9 keV) shows the energy resolution to 0.9 keV (FWHM) at room temperature. (author)