A Contactless Method for High-Sensitivity Measurement of p-n Junction Leakage

Abstract

A contactless p-n, junction leakage measurement method is described that uses low-noise vhf oscillator circuitry to examine the dynamic memory-like behavior of the junctions. This method utilizes the eddy current loading effect, via inductive coupling, in order to determine the leakage-dependent decay time of the photoinduced voltage across the diffused p-n junctions. The contactless measurement is made under low forward bias conditions (≤10 mV) such that this measurement is a function of only generation-recombination processes in the junction depletion region. In the low-noise circuitry, sensitivity is enhanced when the oscillatory amplitude is made directly proportional to the figure of merit Q of the coupled oscillator resonant LC tank. This simple oscillator circuit contains only one JFET and a small number of inductors and capacitors, and is supplied by a constant-current source. Junction decay times between 10-4 and 1 s, corresponding to junction leakages between 10-6 and 1010A/cm2, respectively, have been measured and are in excellent agreement with the derived theory showing the contactless decay time to be inversely proportional to the conventional contacting reverse leakage.