Semiconductor Devices

Semiconductors

In general, semiconductors are inorganic or organic materials that can control their conduction depending on chemical structure, temperature, illumination, and the presence of dopants. The name semiconductor comes from the fact that these materials have electrical conductivity between a metal, like copper, gold, etc., and an insulator, like glass. They have an energy gap of less than 4eV (about 1eV). In solid-state physics, this energy gap or band gap is an energy range between the valence band and conduction band where electron states are forbidden. In contrast to conductors, semiconductors’ electrons must obtain energy (e.g., from ionizing radiation) to cross the band gap and reach the conduction band. The properties of semiconductors are determined by the energy gap between valence and conduction bands.

Semiconductor Devices

Semiconductor devices are electronic components that are made from semiconductor materials, such as silicon. These devices have electrical properties that are between those of conductors (which allow electricity to flow easily) and insulators (which block electricity from flowing). Here are some common semiconductor devices:

1. Diodes: A diode is a two-terminal electronic device that allows current to flow in only one direction. It is made by joining a p-type semiconductor (which has an excess of holes) and an n-type semiconductor (which has an excess of electrons) together.
2. Transistors: A transistor is a three-terminal electronic device that can amplify or switch electronic signals. It is made by joining three layers of semiconductor material together: an n-type layer, a p-type layer, and another n-type layer (for an NPN transistor) or a p-type layer (for a PNP transistor).
3. Integrated Circuits: An integrated circuit (IC) is a miniaturized electronic circuit that is made by combining multiple semiconductor devices, such as diodes, transistors, and resistors, onto a single piece of silicon. ICs are used in a wide range of electronic devices, from computers and smartphones to automobiles and medical equipment.
4. Solar Cells: A solar cell is a semiconductor device that converts sunlight into electricity. It is made by doping a silicon wafer with impurities to create p-type and n-type regions, which create a built-in electric field that separates electrons and holes and generates a voltage.
5. Light-Emitting Diodes (LEDs): An LED is a semiconductor device that emits light when a current flows through it. It is made by doping a semiconductor material with impurities that create a p-n junction, which emits light when an electrical current passes through it.

These are just a few examples of the many semiconductor devices that are used in electronic applications.

Types of Semiconductors

Semiconductors can be classified into two basic types based on their electronic properties:

1. Intrinsic Semiconductors: These are pure semiconductors that are made up of a single element (e.g., Silicon, Germanium) and have no intentional doping with impurities. Intrinsic semiconductors have a specific number of electrons in their valence band and conduction band. They conduct electricity when they are heated, and some electrons gain sufficient energy to break free from their bonds and become free electrons in the conduction band.
2. Extrinsic Semiconductors: These are impure semiconductors that are intentionally doped with impurities to change their electronic properties. Extrinsic semiconductors can be further classified into two types:
   1. p-type semiconductors: In p-type semiconductors, impurity atoms such as boron are introduced into the semiconductor material. These impurities have fewer valence electrons than the semiconductor material, which results in “holes” (absence of electrons) being created in the valence band. These holes can conduct current like positive charge carriers, which gives the material its p-type designation.
   2. n-type semiconductors: In n-type semiconductors, impurity atoms such as phosphorus are introduced into the semiconductor material. These impurities have more valence electrons than the semiconductor material, which creates excess electrons in the conduction band. These excess electrons can conduct current like negative charge carriers, which gives the material its n-type designation.