Question

(i) Draw the circuit arrangement for studying the V - I characteristics of a pn junction diode in

(i) forward and (ii) reverse bias. Briefly explain how the typical V - I characteristics of a diode are obtained and draw these characteristics.

(ii) With the help of necessary circuit diagram explain the working of a photo diode used for detecting optical signal

Answer 1

Reverse biasing 

The VI characteristics are obtained by connecting the battery, to the diode, through a potentiometer the battery, to the diode, through a (or ,rheostat). The applied voltage to the diode is changed. The applied voltage to the diode is changed. The values of current, for different values of voltage, are noted and a graph between V and I is plotted. The V-I characteristics of a diode, have the form the form shown here.

(ii) The circuit diagram, for the photo diode, is shown here.

The photo diode is ilIuminated by optical signal whose photon energy is greater than the energy gap of the semiconductor used.

The electric field, at the junction, separates the electrons and holes and thus gives rise to an emf.

When an external load is connected, a (photo) current is proportional to the intensity of light incident on the photo diode.