Semiconductor Basics and Doping

Study Notes

Semiconductor basics

When an electron moves from the valence band to the conduction band, a vacancy called a "hole" is left behind in the valence band.
Another electron fills this hole, resulting in the creation of a new hole.
Electrons have a negative charge, while holes are considered to have a positive charge.

Intrinsic Semiconductors

An intrinsic semiconductor is a pure semiconductor, like pure silicon (Si) or germanium (Ge).
Silicon and germanium each have four valence electrons – electrons in their outer shell.
Each valence electron forms a covalent bond with electrons in neighboring atoms.
To increase the conductivity of a semiconductor, different elements (impurities or dopants) are added.

Doping

Dopants have a different number of valence electrons, usually +/- 1, to increase the number of free electrons or holes.
Boron (B) has three valence electrons and is a p-type dopant.
Adding boron results in a hole for each boron atom.
Holes attract electrons from neighboring silicon atoms and contribute to current flow.
Arsenic (As) has five valence electrons and is an n-type dopant.
Adding arsenic results in one extra free electron for each arsenic atom, increasing conductivity.

Semiconductor Basics

When an electron moves from the valence band to the conduction band, it leaves behind a vacancy called a "hole" in the valence band.
To fill the space of the missing electron (hole), another electron moves to the hole, resulting in another hole.
An electron carries a negative (-) charge, while the hole is considered to carry a positive (+) charge.
An intrinsic semiconductor is a pure semiconductor, like pure silicon (Si) and germanium (Ge).
Both silicon and germanium have four electrons in their outer shell, known as valence electrons.
Each valence electron forms a covalent bond with the electrons in neighboring atoms, resulting in four covalent bonds.

Doping Semiconductors

To increase the conductivity of a semiconductor, different elements, called impurities or dopants, are added.
These dopants have a different number of valence electrons (usually +/- 1 electron) to increase the number of free electrons or holes.
An element like boron (B), which has three valence electrons, can be used as a dopant.
When boron is added to silicon, three of its valence electrons bond with neighboring silicon atoms, leaving one missing electron (hole) for each boron atom.
The hole attracts electrons from neighboring silicon atoms, becoming a current carrier, similar to electrons, to support current flow.
An element like arsenic (As), which has five valence electrons, can also be used as a dopant.
When arsenic is added to silicon, four of its valence electrons bond with neighboring silicon atoms, leaving one electron for each arsenic atom available and free to conduct electrical current.

Description

Explore the fundamentals of semiconductors, including the movement of electrons and the concept of holes. Understand intrinsic semiconductors and the effects of doping with various elements to enhance conductivity. This quiz covers key principles that are essential for studying semiconductor physics.