semi-conductor

Introduction to Semiconductors

• Electronic materials aim to generate and control electrical current flow.
• Types of electronic materials include:
  • Conductors: low resistance, allow current flow easily
  • Insulators: high resistance, suppress current flow
  • Semiconductors: can either allow or suppress current flow, depending on conditions

Conductors

• Good conductors have low resistance, allowing easy electron flow.
• Best elemental conductors include copper, silver, gold, aluminum, and nickel.
• Alloys like brass and steel are also good conductors.
• Some conductors can be liquid, such as salt water.

Conductor Atomic Structure

• Good conductors' atomic structure usually has only one electron in their outer shell.
• This outer electron, called a valence electron, is easily stripped from the atom, facilitating current flow.

Insulators

• Insulators have high resistance, preventing current flow.
• Common insulators include glass, ceramics, plastics, and wood.
• Most insulators are compounds of multiple elements.
• Atoms are tightly bound in insulators, making it hard to strip electrons for current flow.

Semiconductors

• Semiconductors can be controlled to act as either good conductors or good insulators.
• Common semiconductor elements include carbon, silicon, and germanium.
• Silicon is the most widely used semiconductor.

Periodic Table of Elements

• The provided periodic table highlights semiconductor materials.

Semiconductor Valence Orbit

• The defining characteristic of a semiconductor element is its four valence electrons in the outer orbit. (Silicon is shown as an example.)

Crystal Lattice Structure

• Semiconductors have a unique capability to link atoms together to form a physical structure called a crystal lattice.
• Atoms link together by sharing outer electrons forming covalent bonds.
• This creates a 2D and 3D crystal lattice structure.

Semiconductor Structure

• Semiconductors can have a crystalline or polycrystalline structure.

Semiconductors Can Be Insulators

• Pure semiconductors, like silicon, resist current flow due to tightly bound atoms in their crystal lattice.
• These pure, intrinsic semiconductors are good insulators.

Intrinsic Material

• A perfect semiconductor crystal without impurities or lattice defects is called an intrinsic semiconductor.

Doping

• Doping is the addition of impurities to semiconductors to alter their electrical properties.
• Impurities are different elements to those already present.
• Doping allows semiconductors to either conduct electricity more easily (n-type) or resist electricity more easily (p-type)

Semiconductors Can Be Conductors

• Impurity atoms, such as arsenic, with five valence electrons can be added to silicon to create an abundance of free electrons, becoming n-type semiconductors.
• By adding these impurities, an abundance of 'free' electrons can move around to conduct current.

Improving Conduction by Doping

• Adding impurities, also called dopants, can change the conductivity of semiconductors.
• Elements with 5 outer electrons (donor dopants) contribute extra electrons, increasing conductivity (n-type).
• Elements with 3 outer electrons (acceptor dopants) accept an electron from the silicon, creating holes for increased conductivity (p-type).

Doping - Phosphorus and Arsenic

• Phosphorus and arsenic, added as impurities (dopants), introduce extra electrons, resulting in n-type.
• The extra electron is free to move around and contribute to electric current.
• The phosphorus becomes a positive ion after giving up an electron.

Doping - Boron

• Boron, with three valence electrons, creates holes in the silicon crystal lattice, producing p-type.
• The space left is identified as a hole, behaving like a positive charge and attracting electrons.
• Boron becomes a negative ion after accepting an electron.

Resistance Effects of Doping

• Higher doping concentration generally leads to lower resistance and greater conductivity in semiconductors.
• Doping amount controls semiconductor resistance.

Another Way to Dope

• Impurities with fewer than 4 valence electrons create a hole.
• Creating holes gives them the capability to attract and conduct current.

Types of Semiconductor Materials

• Silicon doped with extra electrons forms N-type semiconductors (N for negative due to the electron charge).
• Silicon with electron-missing "holes" forms P-type semiconductors (P for positive due to the positive charge of the hole).

Current Flow in Semiconductors

• A DC voltage source with a positive terminal attracts free electrons in a semiconductor, creating a positive charge.
• Electrons flow from the negative terminal to the positive in conventional current flow.
• In the semiconductor, 'hole' movement is an important conductor.

In Summary

• Pure semiconductors are insulators.
• Doping changes conductivity, creating N-type (extra electrons) and P-type (missing electrons/holes).
• Increased doping increases conductivity.