Objective: Determination of Energy Band Gap of Silicon, Germanium etc using diodes and light emitting diodes.

Theory: The current-voltage characteristic of a p-n junction can be described by the ideal diode equation

Considering the diode in forward bias, 1 can be neglected in above equation. is proportional to the Boltzmann factor and to  where  is a constant. We may thus write

Neglecting the  dependence of  as compared to the exponential dependence on T and can treat B = A as almost constant. Therefore,

Combining Eqs. (1) and (2), and neglect 1 in Eq. (2), we obtain

Experimentally if the current I is constant, above equation may be rewritten as

where C=ln(I/B). If we rewrite Eq. (3),

we have


which is the linear relation, provided that  is constant. If we compare Eqs. (4) and (1), we see that intercept and slope  We divide b by a and obtain

Equation (5) relates the band gap energy to the experimentally determined values of the parameters a and b in Eq. (1).
The Setup facilitates determination of Energy Band Gap of semiconductors by measuring the voltage drop across sample at a constant current. A graph of V vs T¹ is plotted and ratio of its slope and intercept gives the value of Energy Gap as per equation (5).

• 1.Main unit having digital voltmeter (0-9.99V dc) and micro ammeter (0-999 µA dc), highly stabilized variable power supply (5V)
• 1.Samples (Ge, Si, LEDs),
• 1.Energy controlled hot air oven, Oil and Thermometer.