Product(s) :

Semiconductor Characterization: 4200-SCS

Switching and Control: 7065

Low-Current/High-Resistance: 236, 237, 238

Question : What are techniques to consider for Van der Pauw measurements (high resistivity)?

Answer: The van der Pauw technique for measuring resistivity involves applying a current and measuring voltage using four small contacts. A total of eight measurements are made.

A differential measurement may be required if the sample resistance is of the same magnitude as the isolation of the voltmeter.

A Source-Measure Unit, such as the 236 should be combined with an electrometer (used as a high-impedance buffer) to provide the equivalent of a differential electrometer. The buffer is connected between the sample and the LO Sense terminal of the SMU.

Another approach includes the Model 7065 switching card, a current source and a digital multimeter. The switch card has built-in unity-gain buffers, so differential measurements can be made easily on high resistivity samples. For more information see the Resistivity Measurements section of Keithley's Low Level Measurements handbook.

The model 4200-SCS Semiconductor Characterization System with preamps is also ideal for high resistance samples because of its high input impedance, accuracte low current sourcing. For more information on this approach, read Application Note #2475: Four-Probe Resistivity and Hall Voltage Measurements with the Model 4200-SCS