Detailed Notes on Doping in Semiconductors for JEE Preparation (NCERT Reference: Class 11 and 12)

1. Basics of Semiconductors:

• Key Points:

• Semiconductors are materials with electrical conductivity intermediate between conductors and insulators.

• They have a partially filled valence band and an empty conduction band.

• The bandgap energy determines the semiconductor’s type.

• NCERT Reference: Ch. 14, Semiconductors (Class 11)

2. Types of Doping:

• Key Points:

• Doping is the process of introducing impurities into a semiconductor to modify its electrical properties.

• N-type semiconductors are formed by doping with atoms that have one extra electron in their outermost shell (e.g., phosphorus).

• P-type semiconductors are formed by doping with atoms that have one less electron in their outermost shell (e.g., boron).

• NCERT Reference: Ch. 14, Semiconductors (Class 11)

3. Dopant Materials and Mechanisms:

• Key Points:

• Common n-type dopants: phosphorus, arsenic, antimony

• Common p-type dopants: boron, gallium, indium

• Substitutional doping: dopant atoms replace semiconductor atoms in the crystal lattice.

• Interstitial doping: dopant atoms occupy spaces between semiconductor atoms in the crystal lattice.

• NCERT Reference: Ch. 14, Semiconductors (Class 11)

4. Energy Levels and Band Diagrams:

• Key Points:

• Dopant atoms create impurity energy levels within the semiconductor’s bandgap

• N-type semiconductors have a donor level just below the conduction band.

• P-type semiconductors have an acceptor level just above the valence band.

• The Fermi level shifts towards the conduction band in n-type semiconductors and towards the valence band in p-type semiconductors.

• NCERT Reference: Ch. 14, Semiconductors (Class 11)

5. Effects of Doping on Conductivity:

• Key Points:

• Doping increases the electrical conductivity of semiconductors by increasing the number of charge carriers (electrons in n-type and holes in p-type).

• The conductivity of a semiconductor depends on the dopant concentration and the temperature.

• NCERT Reference: Ch. 14, Semiconductors (Class 11)

6. Formation of p-n Junctions:

• Key Points:

• A p-n junction is formed by joining a p-type semiconductor with an n-type semiconductor.

• The region near the junction is called the depletion region.

• The potential barrier across the depletion region is called the built-in potential.

• NCERT Reference: Ch. 14, Semiconductors (Class 11)

7. Current-Voltage Characteristics of Diodes:

• Key Points:

• A diode is a semiconductor device with two terminals (anode and cathode).

• Under forward bias, the current increases rapidly as the voltage increases (low-resistance state).

• Under reverse bias, the current is very small (high-resistance state).

• The I-V characteristics of diodes are nonlinear.

• NCERT Reference: Ch. 14, Semiconductors (Class 11)

8. Applications of Doped Semiconductors:

• Key Points:

• Doped semiconductors are used in various electronic devices, including diodes, transistors, solar cells, and light-emitting diodes (LEDs).

• Diodes are used to rectify alternating current (AC) to direct current (DC), protect circuits from overvoltage, and detect radio signals.

• Transistors are used to amplify electrical signals, switch electronic circuits, and store digital information.

• Solar cells convert sunlight into electrical energy.

• LEDs emit light when an electrical current passes through them.

• NCERT Reference: Ch. 14, Semiconductors (Class 11), Ch. 15, Communication Systems (Class 12)

9. Device Fabrication Techniques:

• Key Points:

• Semiconductor device fabrication involves several steps, including crystal growth, deposition, lithography, and etching.

• Crystal growth methods: Czochralski method, Bridgeman method, zone refining.

• Deposition techniques: physical vapor deposition (PVD), chemical vapor deposition (CVD).

• Lithography: the process of creating patterns on the semiconductor surface using a photoresist.

• Etching: the process of removing unwanted material from the semiconductor surface using a chemical etchant.

• NCERT Reference: Ch. 14, Semiconductors (Class 11), Ch. 16, Electronic Devices (Class 12)

10. Emerging Materials:

• Key Points:

• Wide-bandgap semiconductors, such as gallium nitride (GaN) and silicon carbide (SiC), are gaining importance in semiconductor doping and device applications.

• These materials have higher breakdown voltages, higher thermal conductivity, and higher electron mobilities than conventional semiconductors like silicon.

• They are used in high-power electronic devices, high-temperature electronics, and optoelectronic devices.

• NCERT Reference: Not covered specifically in NCERT, but supplementary materials and research articles can be consulted.