Semiconductors. (1978)

Punched tape.

Decryption of information from punched tape into text and its printing works automatically.

Graph builder.

Electronic lamp.

Various types of electronic lamps.

An electronic lamp is a glass bulb with an anode, cathode and grid.

The lamp changed all the time, the principle of emission of electrodes by a heated cathode remained unchanged.

The main element of electronic vacuum devices is a filament.

Large-scale operation of the electronic lamp.

The discovery of the phenomenon of the internal photoelectric effect led to the creation of semiconductor technology.

Gramophone.

An old TV, on the screen of which stylized images of a phone, a car, a gramophone are shown.

Calculator.

Let's consider the issues of band representations of semiconductor physics.

Current conductors (razor blade) and dielectrics (glass ball).

The conductivity of semiconductors depends on external influences.

The inner world of the crystal is not quite ordinary.

The laws of quantum mechanics apply here.

As an example, consider silicon, the most common material in the manufacture of semiconductor devices.

Silicon has 14 electrons.

10 of them are in internal orbits.

4 external electrons determine its valence.

Cartoon explaining the structure of the silicon molecule.

In crystalline silicon, valence electrons are socialized.

A cartoon showing this process.

Electrons participate in valence exchange, which cannot lead to an electric current.

In order to understand how semiconductors work, it is necessary to abandon the usual concepts of classical physics.

The energy model of the silicon atom.

This model consists of 3 energy levels.

They are filled with electrons in accordance with the Pauli principle.

At the lower level there are 2 electrons, at the middle 8.

There are 4 electrons at the upper level.

In the process of crystal formation, the energy levels of isolated atoms are transformed into zones of levels.

The zone occupied by valence electrons is called valence.

The free zone closest to it is called the conduction band.

There is an energy interval between them that is inaccessible to electrons.

These are the basic concepts of the zone theory of a solid.

The number of levels that make up the valence band and the conduction band are proportional to the number of atoms forming the crystal.

A band model with a completely filled valence band and a completely empty conduction band is demonstrated.

Notes.

The analogy of the zone model with musical notation.

Comparison of a planar crystal model with a zone model.

Comparing different models of the behavior of valence electrons, it turns out that the energy state of the electron we have noted remains unchanged, while in the system of spatial representations it participates in valence exchange.

In order for the crystal to become electrically conductive, an electron transition from the valence band to the conduction band is necessary.

It is necessary to have a free charge carrier.

The condition for obtaining such an electron is heating.

When heated, the atoms of the crystal begin to vibrate, which leads to the fact that the electron of the valence band receives energy sufficient to transition to the conduction band.

In this case, a free state or a hole is formed in the valence band.

Schematic representation of such an electron transition.

The hole behaves like a positively charged particle.

When an external electric field is applied, free electrons and holes move in opposite directions.

The crystal becomes electrically conductive.

If the crystal contains an admixture of foreign atoms, then impurity levels appear in the forbidden zone.

The electrons of the impurity atoms easily pass into the conduction band.

Impurity atoms turn into positive ions.

Such impurities are called donor or N-type.

Other impurities create permitted levels near the valence band.

Electrons from the valence band move to these levels, and holes form in the zone.

The impurity ion in this case turns out to be negative.

Such impurities are called acceptor or P-type.

The electrical properties of solids depend on the filling of zones and the presence of a band gap in the energy spectrum.

In the isolation ward, the forbidden zone is wide.

In semiconductors already.

In metal, the valence band is partially filled.

Due to the small band gap, semiconductors are extremely sensitive to external influences.

This property of theirs led to the emergence of semiconductor electronics.

In engineering, semiconductor crystals are most widely used, in which regions with various types of impurities are formed.

At the point of contact of the regions with donor and acceptor impurities, free electrons and holes diffuse towards each other.

As a result of recombination, a potential barrier appears in the region of the PH transition.

Before us is a kind of electric valve, the main element of many semiconductor devices.

Various semiconductor elements.