Abstract
Some improvement made on the procedure of measuring the resistivity of semiconductor ma-terial by two- or four- point probe a. c. method is described. In the a. c. measurement, elimination of the current probe stray capacitance to ground is important, and for this purpose a differential amplifier is used in the input circuit. To obtain the accuracy of 2% in error over the whole range, the amplifier must have a good common mode rejection ratio, a linear characteristic over the range of 80 db, and an input resistance greater than 50 megohms, which also reduce the error due to the parasitic ground capacitance of the voltage probe to become less than 0.01 per cent. The measurable range of resistivity is from 0.001 to 10, 000 ohm-cm. The V-I characteristic at each point contact differs depending upon whether the surface is mechanically polished or chemically etched. As the surface becomes cleaner, the rectification becomes remarkably appeared. Measured resistivity of a smooth specimen is always lower than its bulk resistivity because of injection of minority carriers. To minimize such an error, a sandpaper-polished rough surface is to be used and also the output waveform is to be monitored by an oscilloscope. Thus, the reduction of error on contact potential and the raising of sensitivity become easier by the a. c. method than by the d. c. method.
