semiconductor

History

The first experiments with semiconductors began in the 19th century: Faraday noticed that silver sulfide conducts current better when heated. In 1947, Bardeen, Brattain, and Shockley created the first germanium transistor. Since then, silicon has become the basis of electronics. Shuji Nakamura in the 1990s developed bright blue LEDs based on gallium nitride—a semiconductor—for which he received the Nobel Prize.

How it works

In a semiconductor, electrons are in energy bands. There is a valence band, where electrons are tightly bound to atoms, and a conduction band, where they are free. Between them is a forbidden band. An electron can jump across it if it receives energy greater than the band gap width. This is like jumping over a ditch: without a running start (energy), it won't work. By adding impurities (doping), additional steps can be created to facilitate the jump—this is how transistors are made.

History

The first experiments with semiconductors began in the 19th century: Faraday noticed that silver sulfide conducts current better when heated. In 1947, Bardeen, Brattain, and Shockley created the first germanium transistor. Since then, silicon has become the basis of electronics. Shuji Nakamura in the 1990s developed bright blue LEDs based on gallium nitride—a semiconductor—for which he received the Nobel Prize.

How it works

In a semiconductor, electrons are in energy bands. There is a valence band, where electrons are tightly bound to atoms, and a conduction band, where they are free. Between them is a forbidden band. An electron can jump across it if it receives energy greater than the band gap width. This is like jumping over a ditch: without a running start (energy), it won't work. By adding impurities (doping), additional steps can be created to facilitate the jump—this is how transistors are made.

History

Semiconductor properties were first observed by Michael Faraday in 1833 in silver sulfide. In 1874, Karl Braun discovered the rectifying effect at a metal-semiconductor contact. The decisive breakthrough came in 1947 with the invention of the transistor at Bell Labs (Bardeen, Brattain, Shockley). Shuji Nakamura in 1993 made a breakthrough by creating a bright blue LED based on gallium nitride, opening the way to white LED lighting. For this achievement he was awarded the Nobel Prize.

How it works

The conductivity of a semiconductor is determined by the concentration and mobility of free charge carriers. In an intrinsic semiconductor at T>0, electrons transition from the valence band to the conduction band, leaving holes. The carrier concentration obeys the law of mass action: n_i^2 = N_c N_v exp(-E_g/kT). When doped, donors create levels near the conduction band, facilitating thermal ionization. The principle of operation of the p-n junction, the basis of diodes and transistors, relies on diffusion and drift of carriers in an electric field. An important role is played by Coulomb's law, which determines potential barriers, and the Schrödinger equation, which describes the wave functions of electrons in a periodic potential.

Open problems & fun facts

Creation of semiconductors with high mobility at room temperature (e.g., based on graphene); Control of defects in wide-bandgap semiconductors for UV optoelectronics; Development of semiconductors compatible with biological tissues for implantable devices; Search for materials for high-temperature electronics (silicon carbide, diamond)

💡 Semiconductors are used not only in electronics but also in solar cells: photons of light knock electrons from the valence band into the conduction band, creating an electric current. The most common semiconductor—silicon—makes up almost a third of the Earth's crust, literally the sand under our feet!