Question

Draw a circuit diagram to obtain characteristic curve in forward bias of p-n junction diode. Mention the effect of forward bias on depletion layer of the junction.

Hint:

In forward bias, the potential barrier is reduced, allowing current to flow through the diode. At high forward voltages, the current increases rapidly. The diode has negligible current flow below the threshold voltage (0.7V for silicon diodes).

Answer 1

Step 1: Circuit Diagram for Forward Bias of p-n Junction Diode.
To obtain the characteristic curve of a p-n junction diode in forward bias, we need to connect the diode in a circuit with a variable power supply. The positive terminal of the power supply is connected to the p-type side (anode) of the diode, and the negative terminal is connected to the n-type side (cathode).
\begin{center} \includegraphics[width=0.7\linewidth]{pn_diode_forward_bias.png} % Add image of the p-n junction diode in forward bias \end{center}

Step 2: Explanation of Circuit Diagram.
- A power supply provides a varying voltage across the diode.
- The anode of the diode is connected to the positive terminal, and the cathode to the negative terminal of the power supply.
- A milliammeter is connected in series with the diode to measure the current that flows through the circuit.

Step 3: Characteristic Curve.
When the diode is forward biased, the current increases as the applied voltage increases beyond a threshold (typically around 0.7V for silicon diodes). At lower voltages, the current is almost zero, but as the voltage increases, the current increases exponentially. The characteristic curve of a p-n junction diode in forward bias shows this exponential increase.

Step 4: Effect of Forward Bias on the Depletion Region.
- In forward bias, the external voltage decreases the width of the depletion region, allowing more charge carriers to recombine at the junction.
- As the forward voltage increases, the potential barrier decreases, and more charge carriers can cross the junction, leading to an increase in current.

Final Answer: In forward bias, the depletion region becomes narrower, and the current increases exponentially with the applied voltage after a certain threshold.