Four Probe Experiment

We offer Four Probe Method, it is one of the standard and most widely used method for the measurement of resistivity of semiconductors. The experimental arrangement is illustrated. In its useful form, the four probes are collinear. The error due to contact resistance, which is specially serious in the electrical measurement on semiconductors, is avoided by the use of two extra contacts (probes) between the current contacts. In this arrangement the contact resistance may all be high compare to the sample resistance, but as long as the resistance of the sample and contact resistances are small compared with
the effective resistance of the voltage measuring device (potentiometer, electrometer or electronic voltmeter),
the measured value will remain unaffected. Because of pressure contacts, the arrangement is also specially useful for quick measurement on different samples or sampling different parts of the same sample..

The experiment consists of the following:

(i). Four Probes Arrangement, FPA-02:
It has four individually spring loaded probes. The probes are collinear and equally spaced. The probes are mounted in a teflon bush, which ensure a good electrical insulation between the probes.
A teflon spacer near the tips is also provided to keep the probes at equal distance. The whole –arrangement is mounted on a suitable stand and leads are provided for the voltage measurement.

(ii). Sample (Ge-n type)
Germanium crystal in the form of a chip

(iii). Oven FPO-02 (upto 200°C)
It is a small oven for the variation of temperature of the crystal from the room temperature to about 200°C (max.)

(iv). Thermometer DFP 02-THR (0-150°C)

(v). Four Probe Set-up, DFP-02
    The set-up consists of three units in the same cabinet.

(a) Multirange Digital Voltmeter
     Range: X1 (0-200mV) & X10 (0-2V)   
     Resolution: 100mV at X1 range   
     Accuracy: ±0.1% of reading ±1 digit   
     Impedance: 1MΩ
     Display: 3½ digit, 7 segment LED

(b) Constant Current Generator
     Open Circuit: 18V
     Current range: 0-20mA
     Resolution: 10mA
     Accuracy: ±0.25% of the reading ±1 digit
       Load regulation: 0.03% for 0 to full load
     Line Regulation: 0.05% for 10% changes

(c) Oven Power Supply: Built-in for the above oven.

Typical results obtained from this set-up are shown in the datasheet.   

The experimental set-up is complete in all respect.