THIS IS AN ELECTRONIC UNIT THAT USES A FOUR POINT PROBE TO DETERMINE A SEMICONDUCTOR'S CONDUCTIVITY TYPE VIA THE RECTIFICATION METHOD. AN AC VOLTAGE IS APPLIED BETWEEN PROBES 1 AND 3 AND THE RESULTING POTEBTIAL BETWEEN NEEDLES 2 AND 4. THE VOLTAGE DROP V42 IS SMALL WHEN THE AC VOLTAGE AT PROBE 2 IS POSITIVE BECAUSE THE METAL SEMICONDUCTOR JUNCTION IS FORWARD BIASED. BUT FOR NEGATIVE VOLTAGE AT PROBE 2, THE JUNCTION IS REVERSE BIASED. BUT FOR NEGATIVE VOLTAGE AT PROBE 2, THE JUNCTION IS REVERSE BIASED; V IS LARGE AND POSITIVE. THE LARGE POSITIVE AND SMALL NEGATIVE AC V RESULT IN DC COMPONENT WITH THE POLARITY OF THE SEMICONDUCTOR METAL JUNCTION VOLTAGE NECESSARY TO REVERSE BIAS THE JUNCTION. FOR N-TYPE V IS GREATER THAN O, AND FOR P-TYPE V IS LESS THAN O.

CLASSIFICATION IS DETERMINED ACCORDING TO GIRS 1 AND 6 OF THE COMBINED NOMENCLATURE. CN 90308200 FOR MEASURING OR CHECKING SEMICONDUCTOR WAFERS OR DEVICES.