Current noise spectra in CdTe semiconductor diodes

By using a correlation spectrum analyzer, we succeeded in performing direct measurements of the current noise spectra of cadmium telluride (CdTe) diodes, commonly used in gamma-ray spectrometers. The current noise spectra have been measured over a wide range of frequencies, from below 1 Hz up to 100 kHz, and for diode operating points from 0 up to 150 V. The device showed linear I-V characteristics in all the bias range with a dynamic resistance of about 2 G Omega. Around the equilibrium condition (0-0.5 V), the white component of the noise spectrum is in agreement with the Johnson noise associated to the device resistance. As the bias is increased up to 150 V, the white noise level is shown to slowly approach the shot noise behavior. The white noise shows a cut-off frequency consistent with the carriers transit time across the device. In all the nonequilibrium conditions, the noise spectra also show a significant 1/f component whose power density increases with the square of the device current. (C) 2000 American Institute of Physics. [S0021-8979(00)00110-9].