What is a Semiconductor?
A silicon wafer with etched processor cores. Silicon is a semiconductive material.
CREDIT: Oleksiy Mark | Shutterstock
A semiconductor is exactly what its name implies: a material that conducts electrical currents, but only partly. Semiconductors fill a key role in the capabilities of electronic devices. Computers, smartphones and cars all use semiconductors.
The purpose of semiconductors
Semiconductors offer lower resistance to the flow of electricity in one direction, which allows other electrical components like transistors to open and close electrical currents for the purpose of storing information and executing processes. Being able to effectively direct the flow of currents is paramount in electronics.
How a semiconductor works
The functioning of a semiconductor is best explained at an atomic level. In an atom, electrons are organized in layers, the outermost layer being the valence shell. The electrons on this shell are those that allow bonding (i.e., covalent bonds) to form between neighboring atoms. Conductors typically have just one electron contained in the valence shell, whereas semiconductors have four.
If a neighboring atom is of the same type, the valence shell of one atom binds with other atom’s shells, creating structures called crystals. Semiconductors are made of crystals of elements such as germanium and silicon. These materials by themselves, however, are not enough to truly become a semiconductor. Pure crystals are typically anything but electrically conducive. By mixing a crystal with other elements through the process of “doping,” a crystal can become a semiconductor.
Doping and semiconductors
Doping can be used to create both N-type and P-type semiconductors. N-type semiconductors are created by introducing phosphorus, which contains five valence electrons. With the fifth electron remaining unbonded, it behaves like a regular conductor like copper. P-type semiconductors are created by combining boron, which contains only three electrons. By having fewer electrons than the semiconductor, a hole is created, giving a positive charge to the material.
When electrical currents are applied to either N-type or P-type semiconductors, currents flow as they would through a regular conductor. The negative or N-type semiconductor pushes electrons, whereas the positive or P-type semiconductor pulls them. By combining both types of semiconductors together, electrical engineers are able to organize and measure electrical currents.
The history of semiconductors
The discovery of semiconductors cannot be attributed to any one individual. Early references of the material date back to 1782. Michael Faraday became the first individual to witness the semiconductor effect in 1833. As temperature levels decreased, Faraday noted the electrical resistance of materials like silver sulfide decreased.
In 1874, the first semiconductor diode effect was discovered by Karl Braun. He saw electrical currents flowing freely in one direction. It wasn’t until 1901 that an actual semiconductor device was created, called “cat whiskers,” used to detect radio waves. Discoveries like these helped pave the way to electrical devices that made use of semiconductor materials, such as the transistor in 1947.
Semiconductors in transistors
Transistors largely rely on the use of semiconductors in directing the flow of currents. In 1947, researchers at Bell Telephone Laboratories created the transistor, which consisted of two gold foil contacts resting on a germanium crystal. The contacts used the crystal to boost the strength of currents flowing between each contact, allowing for one-way electrical currents through a “sandwich” effect of the crystal being contained between the two metal contact points to further amplify the flow of electricity.