Question

Write the differences between intrinsic semiconductor and extrinsic semiconductor.
OR
What is P-N junction diode? Describe its use as a full wave rectifier with diagram.

Hint:

In a full-wave rectifier, both positive and negative cycles of the input AC are utilized, making it more efficient in converting AC to DC compared to a half-wave rectifier.

Answer 1

a. Differences Between Intrinsic and Extrinsic Semiconductor: 
1. Definition: 
- Intrinsic Semiconductor: An intrinsic semiconductor is a pure semiconductor in which the number of electrons is equal to the number of holes. It does not have any impurities added to it and has relatively low conductivity. Silicon and germanium in their pure forms are examples. 
- Extrinsic Semiconductor: An extrinsic semiconductor is a semiconductor that has been doped with impurities to alter its electrical properties. It has either extra electrons (n-type) or extra holes (p-type) and has higher conductivity than intrinsic semiconductors.
2. Conductivity: 
- Intrinsic Semiconductor: The conductivity of intrinsic semiconductors is low because they have very few charge carriers. 
- Extrinsic Semiconductor: The conductivity of extrinsic semiconductors is higher than intrinsic semiconductors due to the addition of impurities, which provide free charge carriers (electrons or holes).
3. Doping:
- Intrinsic Semiconductor: Intrinsic semiconductors are pure materials and are not doped with any foreign elements. 
- Extrinsic Semiconductor: Extrinsic semiconductors are doped with foreign elements to increase the number of free charge carriers. Doping can create n-type or p-type semiconductors.
4. Charge Carriers: 
- Intrinsic Semiconductor: In intrinsic semiconductors, the charge carriers (electrons and holes) are generated purely by thermal excitation. 
- Extrinsic Semiconductor: In extrinsic semiconductors, the charge carriers (electrons in n-type and holes in p-type) are supplied by the dopant atoms.
b. P-N Junction Diode and its Use as a Full-Wave Rectifier: 
A P-N junction diode is a semiconductor device formed by joining a p-type material (which has an excess of holes) and an n-type material (which has an excess of electrons). The junction between these two materials is called the P-N junction. The P-N junction diode allows current to flow in one direction (forward bias) and blocks current in the opposite direction (reverse bias), making it useful in rectification.
Working as a Full-Wave Rectifier: 
A full-wave rectifier uses both halves of the input AC signal, making it more efficient than a half-wave rectifier. It typically uses two diodes in a bridge configuration to convert the AC signal into a pulsating DC signal.
Working Principle:
1. In the positive half cycle of the input AC signal, current flows through the P-N junction diodes in the direction that allows the current to pass through the load resistor. This results in a positive voltage across the load.
2. In the negative half cycle of the AC input, the diodes conduct in the opposite direction, but due to the arrangement, current still flows through the load resistor, maintaining the same direction of current. This results in a continuous DC output.
The diagram below shows a simple full-wave rectifier circuit with a P-N junction diode: