PHOTOCURRENT TRANSIENTS IN ALMOST IDEAL SILICON P-N-JUNCTIONS

Results obtained from measurements and spectroscopic analysis of current transients induced in almost ideal silicon n(+) - p junctions by infra-red stimulation n illuminating a reverse biased junction by means of an infra-red emitting diode for a few seconds, a current transient is generated which, at 0 degrees C, lasts several hours. This can be decomposed, by means of a proper spectroscopic method, into a sum of four exponential contributions with time constants ranging from tens up to thousands of seconds. Similar dark current transients were already obtained for the same junctions when they were stimulated by a change of the reverse bias voltage, without any optical excitation. The spectroscopy of both optical and voltage induced current transients gives four exponential components with the same time constants. Both the dark current and the photocurrent transients are ascribed to the same SiyOx clusters containing hundreds of Si atoms and four types of single energy level defect centers with different localization. While the voltage induced current transients implicate the activation of such defect centers in the p-region near the n(+) - p interface only, those due to the photostimulation produce their activation throughout the whole n(+) region as well. This fact leads to much greater values for the transient photocurrent in n comparison to those induced by voltage changes and, as a consequence, to greater reliability and accuracy in the measurements and in the results obtained from their analysis. (C) 1995 American Institute of Physics.