Given below is a brief description of the experiments that may be performed.
(a) Reverse saturation current I0 and material constant η
The magnitude of I0 is too small to be measured conveniently and further, it is a function of the applied voltage. The direct measurement of this current is therefore both difficult and erroneous. In the present set-up, readings for the forward V-I characteristics are obtained by 31⁄2 digit DPM for a wide range of currents.
If, V and lnI are plotted on a graph paper a straight line is obtained. This line intersects the current (lnI) axis at lnI0 and its slope ∆V/∆lnI may be solved to compute η.
(b) Energy band-gap and temperature coefficient of the junction voltage The P-N junction under test is kept in a small, fast temperature controlled oven. The temperature is adjustable in the range from room temperature to about 80°C. From the readings of the temperature and junction voltage on digital instruments provided on the panel, the temperature coefficient and energy bandgap are computed.