Semiconductor diode: principle of operation, applications and advantages

A semiconductor diode is a special device with one pn junction, as well as an anode and cathode terminal, which is intended for all kinds of changes in the electrical signal. In most cases, the cell is made of silicon, although other semiconductor materials are sometimes used. Among the main components of the device is a crystalline part with a pn junction.

general information

It should be noted that modern semiconductor diodes are created on the basis of germanium or selenium, as they were more than a hundred years ago. These materials have a specific structure that allows the elements to be used to modernize circuits and electrical appliances, as well as to convert different currents.

There are different types of such inventions in the world, which differ in the material of manufacture, the principle of operation and the scope of application.

Plane and polycrystalline rectifiers are in great demand., which are analogs of bridges. They interact through two contacts.

As for the advantages of devices, they should include:

1. Complete interchangeability. A failed element can be replaced with any other one with the same properties and principle of operation. There are no special requirements for choosing exactly the same model.
2. High throughput.
3. Cheapness and availability. Semiconductor diodes are sold in every electrical store. The cost of such products is from 50 rubles. In addition, they can be removed with your own hands from the schemes of old devices.

Principle of operation

It is not difficult to understand the principle of operation of a semiconductor diode. All you need to do is understand the basic laws of physics and know how some electrical processes occur.

Initially, an electric current acts on the cathode, which causes the heating element to glow. In turn, electrons are emitted from the electrode, and an electric field appears between the two parts.

Anodes with a positive charge act on electrons and attract them, and the generated field acts as a catalyst for such a reaction. Also at this moment, the emission current is formed.

A space-negative charge begins to form in the two electrodes, which can impede the flow of electrons. However, this happens only when the potential of the anode decreases, as a result of which the mass of electrons is not able to cope with negative elements, which makes them move in the opposite order, that is, the electrons return to cathode.

Often, the indicators of the cathodic current are kept at zero - this happens when exposed to particles with a minus charge. As a result, the generated field does not make the electrons move faster, but causes a reverse reaction - it slows them down and forces them back to the cathode. Ultimately, the circuit is opened as the diode remains off.

Device and design

Having dealt with the principle of operation of a semiconductor diode, you can begin to study its device and design. This information will be needed for further use of the diode and a deeper understanding of its operating properties. The element is based on the following components:

1. Outer shell. A small balloon is used as a body. It is completely vacuum and can be glass, metal or ceramic.
2. There are two electrodes inside the structure. The first is used as a cathode with a filament that provides stable electron emission. In its simplest form, it is a thread with a minimum thickness that can glow as the current is applied. But at the present time, models of indirect heating are actively disseminated. Unlike classical types, they are presented in the form of small cylinders with a specific layer where electrons are emitted.
3. As for the second electrode, it is the anode that receives electrons from the cathode. The element has a positive charge and a cylindrical shape. Silicon or germanium is used in the manufacture of a diode crystal.

Areas of application and purpose

The fields of application of semiconductor diodes are very extensive. Today, without them, it is difficult to imagine the work of most electrical devices, and this is not surprising. The elements are used for the manufacture of diode bridges, as well as the following devices:

1. Devices to protect devices against polarity reversal or overloads.
2. Switches.
3. Diode spark protection systems.

As for diode bridges, they are a device of four, six or twelve connected diodes (the exact number of diodes is determined by the type of circuit, which is 1-phase, 3-phase half-bridge or 3-phase full bridge). The system is used as a rectifier and is often installed in car generators. The fact is that the use of such a bridge made it possible to significantly reduce the device and make it more reliable.

Diode detectors consist of diodes and capacitors, which allows low frequency modulation from a variety of signals, including an amplitude modulated radio signal. Devices are indispensable for the functioning of various household appliances, such as a TV or radio. Also, with the help of semiconductor diodes, it is possible to provide full protection against polarity reversal when starting removable inputs and overloads.

The task of diode switches is to switch high frequency signals. To control the circuit, constant electric current, frequency separation and signaling to capacitors are used. Also, on the basis of diodes, a powerful spark protection is created, which prevents overloads and deviations from the permissible voltage limit.

It is practically impossible to do without the use of diodes in modern electronics. Therefore, it is very useful to know how such common devices are arranged, how they work and what they are intended for.

Inclusion methods

The r-n junction is affected by external voltages, as well as magnitude and polarity, which affect the final indicators of the electric current. When using direct connection, the positively charged conductor is connected to the p-type area, and the negative pole to the n-type area. In this case, events will develop as follows:

1. Due to the supplying external voltage in the junction of the r-n-type, an electric field will form, which will be directed in the opposite direction from the diffusion field inside.
2. After that, the field voltage readings will drop noticeably, which will narrow the barrier layer.
3. Further, most of the electrons will be able to move from one region to another, and then return back.
4. The drifting current parameters will remain unchanged, since they are affected only by the number of charged carriers in the r-n region.

With an increase in the reverse voltage, the current will reach the highest rates and go to the next stage - saturation. As the temperature rises, the saturation current parameters increase.

Common malfunctions

Sometimes semiconductor devices stop functioning, which is due to natural depreciation or the end of the established service life. There are other types of malfunctions, which should include:

1. Breakdown of the transition. With this phenomenon, the semiconductor becomes an ordinary conductor that has no specified properties and does not hold the electric current in a specified direction. You can solve the problem with a standard multimeter that beeps and determines the resistance level.
2. Break of the transition. It is a reverse process, as a result of which the device turns into an insulator. In this case, the electric current is passed in only one direction. To determine the location of the break, it is necessary to use a tester with working probes. If these elements are of insufficient quality, then it will not be possible to carry out an accurate and correct diagnosis.
3. Violation of tightness. Any leakage is a serious threat to the normal operation of semiconductor devices.

Breakdown types

There are several types of breakdowns that occur as the reverse current increases. These include:

1. Thermal breakdowns.
2. Electrical breakdowns.

The first danger occurs with unbalanced operation of the heat sink or with overheating of the r-n-junction due to the effect of excessively high current values. The problem of thermal runaway can lead to a host of unpleasant consequences, including:

1. Growth of vibrations of atoms from the composition of the crystal.
2. Interaction of electrons with a conductive region.
3. The rapid rise in temperature indicators.
4. Deformation processes in the structure of crystals.
5. Complete damage to the radio component.

As for the electrical breakdown, it cannot be called an irreversible process, because with such a nuisance, the crystal remains operational. Therefore, timely measures taken will save the diode from destruction, as well as extend its service life.

Depending on the type, electrical breakdowns are tunnel and avalanche. In the first case, the trouble develops due to the passage of an excessively high voltage through narrow junctions, as a result of which electrons freely slip through the breakdown. Such defects are formed when a large number of impurities appear in the molecules. The phenomenon causes an increase in reverse current and a decrease in voltage.

As for avalanche breakdowns, they occur due to the influence of strong fields, which accelerate the carrier to peak performance, and then knock out the mass of valence electrons from the atoms. Because of this, electrons fall into the conductive region, losing their properties. The specific behavior, reminiscent of the nature of the avalanche descent, came to be called avalanche breakdown.

Without a doubt, modern electrical appliances and various radio engineering inventions cannot fully function without semiconductor diodes. And in order to extend the service life of household appliances with these elements, you need to know about the principle of their operation, the main malfunctions and how to deal with them.