πŸ’» Physics β€” Class XII

Semiconductor Electronics

From semiconductor materials to diodes, transistors, and logic gates β€” the building blocks of modern electronics

πŸ“– Chapter 14 ⏱ ~55 min read 🏷️ Electronics

Table of Contents

  1. Introduction
  2. Classification of Materials
  3. Extrinsic Semiconductors
  4. p-n Junction Diode
  5. Rectifier Circuits
  6. Zener Diode
  7. Transistor (BJT)
  8. Logic Gates

14.1 Introduction

Devices in which a controlled flow of electrons can be obtained are the basic building blocks of all the electronic circuits. Before the discovery of transistor in 1948, such devices were mostly vacuum tubes. The invention of the transistor revolutionised electronics, leading to miniaturisation and the modern digital age.

14.2 Classification of Materials

Semiconductor electronics
Figure 14.1 β€” p-n junction diode, diode symbol, and key semiconductor devices
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Conductors

Very low resistivity (~10⁻⁸ Ω·m). Free electrons flow easily. Examples: Cu, Ag, Al.

πŸ”΄

Insulators

Very high resistivity (>10¹⁰ Ω·m). No free electrons. Examples: rubber, glass, diamond.

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Semiconductors

Intermediate resistivity (~10⁻⁴ to 10⁴ Ω·m). Si, Ge, GaAs. Band gap ~1 eV.

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Intrinsic vs Extrinsic

Intrinsic: pure. Extrinsic: doped with impurities (n-type or p-type).

14.3 Extrinsic Semiconductors

14.4 p-n Junction Diode

A p-n junction is formed when p-type and n-type semiconductors are joined. The depletion region creates a potential barrier:

Vβ‚€ = (kT/e) ln(NₐN_d/nα΅’Β²)
Vβ‚€ β‰ˆ 0.7V for Si, 0.3V for Ge. Forward bias reduces barrier; reverse bias increases it.
⚑ Forward vs Reverse Bias

Forward: p connected to +, n to βˆ’. Low resistance, current flows easily.
Reverse: p connected to βˆ’, n to +. High resistance, only tiny leakage current flows.

14.5 Rectifier Circuits

A rectifier converts AC to DC using diodes:

14.6 Zener Diode

A Zener diode is designed to operate in reverse breakdown. It maintains a constant voltage (Zener voltage) across its terminals:

V_Z = constant (in breakdown region)
Used as voltage regulator. Current changes but voltage remains nearly constant.

14.7 Transistor (BJT)

A bipolar junction transistor (BJT) has three terminals: emitter, base, and collector:

I_C = Ξ²I_B | I_E = I_B + I_C
Ξ² = current gain (typically 50-200). Small base current controls large collector current β†’ amplification.

14.8 Logic Gates

Logic gates are the building blocks of digital circuits, performing Boolean operations on binary inputs:

GateSymbolTruth TableOutput
ANDA Β· B00β†’0, 01β†’0, 10β†’0, 11β†’1Both inputs must be 1
ORA + B00β†’0, 01β†’1, 10β†’1, 11β†’1Either input must be 1
NOTΔ€0β†’1, 1β†’0Inverts the input
NAND(A Β· B)'00β†’1, 01β†’1, 10β†’1, 11β†’0Negative AND
NOR(A + B)'00β†’1, 01β†’0, 10β†’0, 11β†’0Negative OR
Ch 13 β€” Nuclei Back to Ch 1 β€” Electric Charges

Physics Class XII β€” Chapter 14: Semiconductor Electronics

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