Educational film for university students on the course "General Physics". About the nature of electrical conductivity of solids using the technology of modern physical experiment.
Punched tape.
Automatically deciphers information from punched tape into text and prints it out.
Plotter.
Electron tube.
Different types of electron tubes.
An electron tube is a glass bulb with an anode, cathode, and grid.
The tube has been constantly changing, but the principle of emission of electrodes by a heated cathode has remained unchanged.
The main element of electronic vacuum devices is the filament.
Close-up of an electron tube.
The discovery of the internal photoelectric effect led to the creation of semiconductor technology.
Gramophone.
An old TV set with stylized images of a telephone, car, and gramophone on its screen.
Calculator.
Let's consider 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 a crystal is not quite ordinary.
The laws of quantum mechanics operate here.
As an example, let's consider silicon, the most common material in the production of semiconductor devices.
Silicon has 14 electrons. 10 of them are in internal orbits. 4 outer electrons determine its valence.
Cartoon explaining the structure of the silicon molecule.
In crystalline silicon, valence electrons are shared.
Cartoon showing this process.
Electrons participate in valence exchange, which cannot lead to the emergence of electric current.
To understand how semiconductors work, you need to abandon the usual ideas of classical physics.
Electrical engineering, Electronic tubes, Quantum Mechanics
Energy model of the silicon atom.
This model consists of 3 energy levels.
They are filled with electrons in accordance with the Pauli principle.
The lower level has 2 electrons, the middle level has 8. The upper level has 4 electrons.
During crystal formation, the energy levels of isolated atoms are transformed into level zones.
The zone occupied by valence electrons is called the valence zone.
The free zone closest to it is called the conduction zone.
Between them is an energy interval inaccessible to electrons.
These are the basic concepts of the band theory of solids.
The number of levels that make up the valence zone and conduction zone is proportional to the number of atoms that form the crystal.
A band model with a completely filled valence zone and a completely empty conduction zone is demonstrated.
Notes.
Analogy of the band model with musical notation.
Comparison of a planar model of a crystal with a band model.
Comparing different models of valence electron behavior, 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.
For a crystal to become electrically conductive, an electron must move from the valence band to the conduction band.
A free charge carrier must appear.
The condition for obtaining such an electron is heating.
When heated, the crystal atoms begin to oscillate, which leads to the electron of the valence band receiving energy sufficient to move to the conduction band.
In this case, a free state or hole is formed in the valence band.
Schematic representation of such a transition of electrons.
The hole behaves like a particle charged positively.
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.
Electrons of the impurity atoms easily move to the conduction band.
Impurity atoms turn into positive ions.
Such impurities are called donor or N-type.
Other impurities create allowed levels near the valence band.
Electrons from the valence band move to these levels, and holes are formed in the band.
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 the bands and the presence of a forbidden band in the energy spectrum.
In an insulator, the forbidden band is wide.
In semiconductors, it is narrower.
In a metal, the valence band is partially filled.
Because of the small width of the forbidden band, semiconductors are extremely sensitive to external influences.
This property led to the emergence of semiconductor electronics.
In technology, semiconductor crystals are most widely used, in which areas with different types of impurities are formed.
At the point of contact between areas with donor and acceptor impurities, free electrons and holes diffuse towards each other.
As a result of recombination, a potential barrier arises in the PN junction region.
Before us is a kind of electric valve, the main element of many semiconductor devices.
Various semiconductor elements.
Crystal, Electron, Hole, Semiconductors, Band theory of solids