Edge injection currents and their effects on 1/ f noise in planar Schottky diodes

Abstract

A technique has been devised whereby the foreward bias edge current of a planar Schottky diode can be separated from the area current. The saturation current density and ideality factor of this edge current have been measured, the edge saturation current density being related to the area saturation current density by a newly defined edge figure of merit, M e . The area current agrees very closely with the thermionic emission Schottky diode equation, whereas the edge currents exhibit serious departures from this equation. No guard rings or process steps other than those normally used to fabricate diodes are needed to obtain these measurements. An ultra-low-noise preamplifier has been constructed which is sufficiently sensitive to detect the difference between the thermal noise of a short and a 5 ohm resistor. Noise power levels approaching case1 2 kT (pure shot noise) have been observed in unpassivated Schottky diodes. The low frequency noises (1/ f noise) of planar Schottky diodes has been measured and correlated with the edge currents, the correlation being expressed in the form of a newly defined noise figure of merit, M n . The technique and figures of merit are universally applicable to all forms of planar diode structures, including Schottky barrier and diffused junction types.