1/f Conductance noise in stabilized amorphous selenium

Abstract

We report measurements of low-frequency conductance fluctuations in samples of amorphous selenium alloys that find use in direct-conversion, flat-panel X-ray image detectors. The signal-to-noise ratio of these detectors depends in part on the fluctuations in the so-called dark current that flows through the selenium layer; proper modeling of the detector performance requires measurements of this noise signal. The conductance noise was measured for various applied voltages ranging from 400 to 2000V that produced dark currents ranging from 10−9 to 10−6A. The noise power density spectrum varies approximately as 1/fα from 0.5Hz to 1kHz with α in the range from 0.77 to 1.5. The noise spectrum depends on resting time after application of the voltage and on the metal used for the electrodes which implies that the noise is controlled by the metal semiconductor interface. Integration of the noise power density over the measured frequency range yields an rms fluctuation of the dark current that can be as large as 1% of the average value.