What are Semiconductors?

A semiconductor is actually a material with electrical conduction between that of the conductor, such as the metal, and the insulator, such as wood or plastic. Due to their special property – variable conductivity, semiconductors have become an importance in today’s electronics. This semiconductor cannot allow free passage for electric current like conductors, nor can it completely stop it, as is the case of insulators.

Silicon (Si), and germanium (Ge) have, of course been the most common semiconductor materials but gallium arsenide (GaAs) compounds are increasingly used in modern electronics.

A Brief History of Semiconductors

The development of semiconductors has shaped many modern electronics. Below is a brief history of this fascinating development:

19th Century: Early Discoveries

It is evident that the earliest discovery related to semiconductor properties existed in the early 19th century. In 1833, British scientist Michael Faraday discovered the property wherein electrical resistance in silver sulfide decreases as the temperature increases.
By the late 1800s, researchers such as Karl Ferdinand Braun had recorded the rectifying behavior of materials such as selenium and copper oxide, paving the way for later use of semiconductors in the world of electronics.

Rise of Solid-State Physics in the Early 20th Century

In the early 20th century, scientists began to explore the atomic structure of the materials. Quantum mechanics helped explain to some extent how material conduction might arise, opening the door for a slightly better understanding of semiconductor properties.
Julius Lilienfeld filed a patent for the first field-effect transistor in 1929 although never constructed until decades later.

1940s: The Semiconductor Industry Becomes Born

During World War II, it was felt that much better systems for radar and communication were very urgently needed, which thus pushed further into solid-state electronics. In 1947, at Bell Labs, John Bardeen, Walter Brattain, and William Shockley discovered the transistor with germanium as a semiconductor. This was the actual beginning of the semiconductor industry and led them to receive the Nobel Prize in Physics in 1956.

1950s-1960s: Silicon Revolution

The first main semiconductor material was developed with silicon in the 1950s. Silicon was more abundant, and its properties were also much better suited for making electronic devices than germanium.
In 1958, Texas Instruments engineer Jack Kilby designed and developed the first integrated circuit or IC, which consisted of several transistors put together in one piece of silicon. Nearly at the same time as the invention of the first IC, Robert Noyce of Fairchild Semiconductor produced a similar silicon product that eventually led to the microchip.

1970s-Present: The Era of the Integrated Circuit and On

The microprocessor, sparked by Intel’s 4004, brought the electronics revolution of the 1970s and started off the personal computer revolution.

From the 1980s to the present, semiconductors have been the backbone that enabled development in computing, telecommunications, and consumer electronics. Moore’s Law predicted the exponential rise in the number of transistors on a chip in the industry and thus drove innovation in its field.
Semiconductors lie at the center of today’s technologies: artificial intelligence, 5G communications, and quantum computing. The evolving future applications are founded upon the research of new materials such as gallium nitride (GaN) and graphene.
Semiconductor history reflects rapid technological development, transforming how we live, work, and communicate with each other.

Types of Semiconductors

Intrinsic Semiconductor

Intrinsic semiconductors are the pure semiconductors. No impurities are added in these. Silicon (Si) and Germanium (Ge) are the most common Intrinsic semiconductors.

In intrinsic semiconductors, conduction of electricity is purely dependent on the temperature variation.

At higher temperatures, some electrons gain enough energy to break free of their atomic bonds, becoming free electrons (negative charge carriers) or holes (positive charge carriers).

The number of electrons is equal to the number of holes, and thus, their electrical neutrality is balanced.

Extrinsic Semiconductors

These are the semiconductors whose conductivity can be increased by introducing small amount of impurities in it. They are also known as impure semiconductors.

The process by which impurities are added in a semiconductor is known as Doping.

1. n-type Semiconductor

An n-type semiconductor is a doped material, doped with elements carrying more valence electrons than the semiconductor being doped. For instance, silicon (Si) or germanium (Ge). An n-type semiconductor has additional charge carriers of either electrons or holes as a result of the impurities added.

Free electrons are the majority charge carriers and holes are the minority charge carriers.

The overall charge of an n-type semiconductors remains neutral. It is because the addition of dopant atom does not introduce any net charge. It simply creates free electrons.

2. p-type Semiconductor

A p-type semiconductor is an extrinsic semiconductor. It carries doping with elements having fewer valence electrons than the semiconductor material itself. Eg. silicon (Si) or germanium (Ge). This introduces “holes” positive charge carriers into the material which increases its conductivity.

Holes are the majority charge carriers and electrons are the minority charge carriers.

The overall charge of a p-type semiconductor remains neutral. The addition of dopant atoms does not introduce any net charge; it merely creates holes as charge carriers.

How do Semiconductors Work?

The conductivity of semiconductors depends on the movement of electrons and holes. In an intrinsic semiconductor, thermal energy excites some electrons, causing them to jump from the valence band to the conduction band, leaving behind holes in the valence band. The free electrons and holes move in opposite directions when an electric field is applied, resulting in electrical current.

For extrinsic semiconductors, doping introduces additional charge carriers (electrons in N-type and holes in P-type), enhancing the material’s conductivity. This characteristic allows semiconductors to be engineered for specific purposes in electronic devices.

Common Semiconductor devices

1. Diodes
2. Transistors
3. Integrated Circuits (ICs)

Applications of Semiconductors

Microprocessors: The brains of computers made using millions of tiny transistors on semiconductor chips.

Solar Cells: Convert sunlight into electrical energy using the photovoltaic properties of semiconductors.

LEDs (Light Emitting Diodes): Use semiconductors to produce light when an electric current passes through them.

Sensors: Semiconductor devices used to detect changes in the environment, such as temperature, light, and pressure.

Conclusion

Understanding semiconductors is important for understanding the operation of modern electronic devices. Their salient properties, most notably variable conductivity, make them indispensable in a wide range of applications – from simple diodes to complex microprocessors. The only question is what the role of semiconductors will eventually be as technology advances. Semiconductors will certainly remain one of the most fascinating topics for studying physics and electronics students.