Experimental analysis of current noise spectra in CdTe detectors

In this paper we analyze in detail a peculiar behavior of CdTe detectors, namely the fact that in conjunction with a typical resistive electrical characteristic in which the current is proportional to the externally applied biasing voltage through an equivalent detector resistance, the detector shows a noise level well above the corresponding Johnson noise and close to the shot noise of the standing current. By using a correlation spectrum analyzer, a careful and extensive experimental analysis of the current noise behavior of CdTe detectors for X and gamma ray has been performed. The current noise spectra have been measured over a wide range of frequencies, from below 1Hz up to 100kHz and operating points from 0V up to 150V. In addition to a strong 1/f component, a white noise is present at the level of the shot noise of the standing current and extending in frequency for a limited range related to the carriers transit time across the detector.