Notes from Toppers
Detailed Notes on Doping in Semiconductors for JEE Preparation (NCERT Reference: Class 11 and 12)
1. Basics of Semiconductors:
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Key Points:
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Semiconductors are materials with electrical conductivity intermediate between conductors and insulators.
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They have a partially filled valence band and an empty conduction band.
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The bandgap energy determines the semiconductor’s type.
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NCERT Reference: Ch. 14, Semiconductors (Class 11)
2. Types of Doping:
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Key Points:
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Doping is the process of introducing impurities into a semiconductor to modify its electrical properties.
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N-type semiconductors are formed by doping with atoms that have one extra electron in their outermost shell (e.g., phosphorus).
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P-type semiconductors are formed by doping with atoms that have one less electron in their outermost shell (e.g., boron).
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NCERT Reference: Ch. 14, Semiconductors (Class 11)
3. Dopant Materials and Mechanisms:
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Key Points:
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Common n-type dopants: phosphorus, arsenic, antimony
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Common p-type dopants: boron, gallium, indium
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Substitutional doping: dopant atoms replace semiconductor atoms in the crystal lattice.
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Interstitial doping: dopant atoms occupy spaces between semiconductor atoms in the crystal lattice.
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NCERT Reference: Ch. 14, Semiconductors (Class 11)
4. Energy Levels and Band Diagrams:
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Key Points:
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Dopant atoms create impurity energy levels within the semiconductor’s bandgap
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N-type semiconductors have a donor level just below the conduction band.
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P-type semiconductors have an acceptor level just above the valence band.
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The Fermi level shifts towards the conduction band in n-type semiconductors and towards the valence band in p-type semiconductors.
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NCERT Reference: Ch. 14, Semiconductors (Class 11)
5. Effects of Doping on Conductivity:
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Key Points:
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Doping increases the electrical conductivity of semiconductors by increasing the number of charge carriers (electrons in n-type and holes in p-type).
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The conductivity of a semiconductor depends on the dopant concentration and the temperature.
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NCERT Reference: Ch. 14, Semiconductors (Class 11)
6. Formation of p-n Junctions:
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Key Points:
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A p-n junction is formed by joining a p-type semiconductor with an n-type semiconductor.
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The region near the junction is called the depletion region.
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The potential barrier across the depletion region is called the built-in potential.
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NCERT Reference: Ch. 14, Semiconductors (Class 11)
7. Current-Voltage Characteristics of Diodes:
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Key Points:
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A diode is a semiconductor device with two terminals (anode and cathode).
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Under forward bias, the current increases rapidly as the voltage increases (low-resistance state).
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Under reverse bias, the current is very small (high-resistance state).
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The I-V characteristics of diodes are nonlinear.
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NCERT Reference: Ch. 14, Semiconductors (Class 11)
8. Applications of Doped Semiconductors:
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Key Points:
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Doped semiconductors are used in various electronic devices, including diodes, transistors, solar cells, and light-emitting diodes (LEDs).
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Diodes are used to rectify alternating current (AC) to direct current (DC), protect circuits from overvoltage, and detect radio signals.
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Transistors are used to amplify electrical signals, switch electronic circuits, and store digital information.
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Solar cells convert sunlight into electrical energy.
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LEDs emit light when an electrical current passes through them.
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NCERT Reference: Ch. 14, Semiconductors (Class 11), Ch. 15, Communication Systems (Class 12)
9. Device Fabrication Techniques:
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Key Points:
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Semiconductor device fabrication involves several steps, including crystal growth, deposition, lithography, and etching.
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Crystal growth methods: Czochralski method, Bridgeman method, zone refining.
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Deposition techniques: physical vapor deposition (PVD), chemical vapor deposition (CVD).
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Lithography: the process of creating patterns on the semiconductor surface using a photoresist.
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Etching: the process of removing unwanted material from the semiconductor surface using a chemical etchant.
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NCERT Reference: Ch. 14, Semiconductors (Class 11), Ch. 16, Electronic Devices (Class 12)
10. Emerging Materials:
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Key Points:
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Wide-bandgap semiconductors, such as gallium nitride (GaN) and silicon carbide (SiC), are gaining importance in semiconductor doping and device applications.
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These materials have higher breakdown voltages, higher thermal conductivity, and higher electron mobilities than conventional semiconductors like silicon.
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They are used in high-power electronic devices, high-temperature electronics, and optoelectronic devices.
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NCERT Reference: Not covered specifically in NCERT, but supplementary materials and research articles can be consulted.