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The metal-semiconductor contacts used in dopant profiling by the spreading resistance technique are point contact rectifiers. Several interfering effects normally associated with point contact diodes, e.g., conductivity modulation through the injection of high densities of excess carriers, local heating of the sample, high-field mobility variation, etc., are avoided in making spreading resistance measurements by using a voltage of only 5 mV across the probes. However, when a spreading resistance system is operated in an environment containing high levels of radio frequency radiation, AC currents are induced in the probes and the semiconductor sample. And, at least for some types of spreading resistance contacts, these currents are rectified and result in significant additional DC voltages across the metal-semiconductor junctions. The maximum DC level observed to date due to RF pickup is about 10 mV. This paper presents a discussion of some of the effects observed as a result of pickup from one particular (500 MHz) source. Also, several practical ways to determine when RF pickup is present and how to reduce or eliminate it are presented.
spreading resistance, dopant profiling, point contact diodes, radio frequency noise, measurements
President, Solid State Measurements, Inc., Monroeville, PA