TIP1123 Chapter 10_Electronics

10.0 Introduction to Electronics

• Overview of Chapter 10 focusing on electronics and semiconductors, particularlydiodes.

10.1 Atomic Number

• Atomic number (Z): Number of protons in the nucleus of an atom.

• Arrangement of elements in the periodic table is based on atomic number.

• Neutral atoms have equal numbers of protons and electrons, net charge = 0.

10.2 Electron Shells & Orbit

• Bohr Model: Electrons orbit the nucleus at specific, discrete distances known as shells.

• Each shell has a maximum number of electrons it can hold; examples include:

  • Copper: 2, 8, 18, 1

  • Silicon: 2, 8, 4

10.3 Valence Electrons

• Electrons in the outermost shell (valence shell) determine chemical reactions and electrical properties.

• Valence electrons are less tightly bound to the atom, contributing to bonding behavior.

10.4 Ionization

• When an atom absorbs external energy, valence electrons can gain enough energy to escape from the atom, resulting in ionization.

• This leaves a positively charged ion and a free electron.

Conduction

Room temperature, few electrons can acquire enough thermal energy to reach conduction band.

• Cause some valence electrons to gain sufficient energy to jump gap from valence band to conduction band (free electrons) Hole is left in valence band

• every electron moved to conduction band left 1 hole in valence band = electron hole pair

• Free electrons = conduction electrons

Recombination

• conduction band electron lose energy and fall back to hole in valence band

10.5 Semiconductors & Semiconductor Materials

• Materials classified as:

  • Conductors: e.g., Copper, aluminum, allows free movement of electric charges.

  • Insulators: e.g., Glass, rubber, restricts charge movement.

  • Semiconductors: Exhibit properties intermediate between conductors and insulators, typically made of silicon or germanium.

10.6 Electron & Hole Current

• In intrinsic semiconductors, applying voltage allows free electrons in the conduction band to move, producing an electric current.

• Hole current occurs when valence electrons move into holes, creating new holes and effectively causing holes to move through the semiconductor.

10.7 Doping

• Doping: The process of adding impurities to a pure semiconductor to enhance its conductivity.

  • Intrinsic: Naturally occurring semiconductors.

  • Extrinsic: Semiconductors modified by doping.

• Types of Doping:

  • Trivalent Doping (3 valence electrons): Results in p-type semiconductors (e.g., Al, B).

  • Pentavalent Doping (5 valence electrons): Results in n-type semiconductors (e.g., P, As).

10.8 N-type Semiconductor

• Formed by adding pentavalent impurities, increasing the number of conduction electrons (e.g., Phosphorus, Arsenic).

• Majority carriers in n-type materials are electrons.

10.9 P-type Semiconductor

• Formed by adding trivalent impurities, creating holes (e.g., Boron, Aluminum).

• Majority carriers in p-type materials are holes.

• Hole conduction densities>electrons

10.10 Diode Basics

• Definition: Two-terminal device that conducts current in one direction.

• An ideal diode has zero resistance in the forward direction and infinite resistance in reverse.

Diode Functions

• Blocks current in one direction and allows it to flow in the opposite direction, protecting circuits (e.g., in battery-operated devices).

Diode Construction

• Consists of a pn junction; one half n-type (cathode) and the other p-type (anode).

• Diode symbol represents cathode (K) and anode (A).

• Resistor: limit forward bias current to not overheat and damage pn junction

Forward and Reverse Bias

• Forward Bias: Positive voltage connected to the anode, allowing current flow.

• Reverse Bias: Positive voltage connected to the cathode, resulting in minimal current, approximately zero.