AIM:- Determination of the band gap of a semiconductor by Four Probe Set-Up

APPARATUS :- Probes Arrangement, Sample, Oven, Four Probe Set-up consisting i) Multirange Digital Voltmeter, ii) Constant Current Generator and iii) Oven Power Supply

FORMULA :-
      

PROCEDURE:-

1. Put the sample on the base plate of the four probe arrangement. Unscrew the pipe holding the four probes and let the four probes rest in the middle of the sample. Apply a very gentle pressure on the probes and tighten the pipe in this position. Check the continuity between the probes for proper electrical contacts.

2. Connect the outer pair of probes (green/black leads) to the constant current power supply and the inner pair (red/black leads) to the probe voltage terminals.

3. Place the four probe arrangement in the oven and fix the thermometer in the oven through the hole provided.

4. Switch on the ac mains of Four Probe Set-up and put the digital panel meter in the current measuring mode through the selector switch. In this position LED facing mA would glow. Adjust the current to a desired value (say 5 mA).

5. Now put the digital panel meter in voltage measuring mode. In this position LED facing mV would glow and the meter would read the voltage between the probes.

6. Connect the oven power supply. Rate of heating may be selected with the help of a switch - Low or High as desired. Switch on the power to the Oven. The glowing LED indicates the power to the oven is 'ON'.

7. As the temperature of the oven and hence that of the semiconductor sample rises, the voltage decreases. The voltage value for every 10⁰C interval are recorded. The heating is done upto 150⁰C. The observations are recorded in table.

GRAPH:-
Plot a graph of log₁₀p against 10³/T.

CALCULATIONS:-

RESULT:-
The band gap of given semiconductor is found to be      eV.

PRECAUTIONS:-
The Ge crystal is very brittle. Therefore, use only the minimum pressure required for proper electrical contacts.