Pulse diodes. What is the difference between a pulse diode and a rectifier diode?

Pulse diode – This is a diode with short transient duration, designed for use in pulsed operating modes. Οʜᴎ are used as switching elements (for example, in computers), for detecting high-frequency signals and for other purposes.

At rapid changes voltage across the diode in the - junction, transient processes occur due to two main processes. The first is the accumulation of non-base carriers in the base of the diode when it is directly turned on, ᴛ.ᴇ. diffusion capacitance charge. And when the voltage changes to the opposite (or when it decreases), this charge dissolves. The second phenomenon is the recharging of the barrier capacitance, which also does not occur instantly, but is characterized by a time constant, where is the differential resistance of the diode (resistance across alternating current), a - barrier capacitance - transition.

The first phenomenon plays a major role at high densities of forward current through the diode, the charge of the barrier capacitance in in this case plays a minor role. At low current densities, transient processes in the diode are determined by the second phenomenon, and a secondary role is played by the accumulation of non-base charge carriers in the base.

Let's consider the process of switching a diode from a state of high conductivity (diode open) to a state of low conductivity (diode closed) (Figure 1.11). When direct voltage is applied, a significant forward current arises, which leads to the accumulation of non-base charge carriers in the base area (this is a high-resistance n- region).

When a diode switches from the forward direction to the reverse direction, at the initial moment a large reverse current flows through the diode, limited mainly by the volumetric resistance of the base. Over time, the minority carriers accumulated in the base recombine or leave through the junction, and the reverse current decreases to its stationary value. This entire process takes reverse resistance recovery time– time interval from the moment the current passes through zero after switching the diode until the reverse current reaches the specified value low value. This is one of the basic parameters of pulsed diodes, and according to its value they are divided into six groups: >500 ns; =150…500 ns;=30…150 ns, =5…30 ns; =1…5 ns and<1 нс.

Figure 1.11 - The process of switching a diode from open to closed state

When a current pulse is passed in the forward direction, a voltage surge is observed at the first moment after switching on (Figure 1.12), which is associated with an increase in voltage until the accumulation of non-base carriers in the base of the diode ends. After this, the base resistance decreases and the voltage decreases.

Figure 1.12 -. The process of switching a diode from a closed state to an open state

This process is characterized by the second parameter of the pulse diode - forward voltage establishment time, equal to the time interval from the beginning of the current pulse until the specified value of the forward voltage is reached.

The values of these parameters depend on the structure of the diode and on the lifetime of non-base charge carriers in the diode base. To reduce the lifetime of non-base carriers, a small amount of gold impurity is introduced into the base. Gold atoms serve as additional recombination centers; as a result of their introduction, the lifetime of charge carriers and, consequently, the diffusion capacity of the transition decreases. Reducing the barrier capacity is achieved by technological and constructive methods. Pulse diodes are manufactured on the basis of planar technology, epitaxial growth, and ion beam technology. The main semiconductor material in this case is silicon.

In high-speed pulse circuits, Schottky diodes (Figure 1.13) are widely used, in which the transition is made on the basis of a metal-semiconductor contact. The symbol is shown in Fig. 16.

Figure 1.13 - Schottky diode symbol

Structurally, Schottky diodes are made in the form of a low-resistance silicon wafer, on which a high-resistance epitaxial film with electrical conductivity of the same type is applied. A layer of metal is applied to the surface of the film by vacuum deposition.

Schottky diodes are also used in high current rectifiers and logarithmic devices.

Pulse diodes - concept and types. Classification and features of the category "Pulse Diodes" 2017, 2018.

A pulse diode is a diode with short transient duration, designed for use in pulsed operating modes. They are used as switching elements, for detecting high-frequency signals and for other purposes. With rapid changes in voltage across the diode in the pn junction, transient processes occur due to two main processes. The first is the accumulation of minority carriers in the base of the diode when it is directly turned on, i.e. diffusion capacitance charge. And when the voltage changes to the opposite (or when it decreases), this charge dissolves. The second phenomenon is the recharging of the barrier capacitance, which also does not occur instantly, but is characterized by a time constant t=rd*Cbar, where rd is the differential resistance of the diode (AC resistance), and Cbar is the barrier capacitance of the pn junction. The first phenomenon plays a major role at high densities of forward current through the diode; the charge of the barrier capacitance in this case plays a secondary role. At low current densities, transient processes in the diode are determined by the second phenomenon, and the accumulation of minority charge carriers in the base plays a secondary role.

Consider the process of switching a diode from a high conductivity state (diode open) to a low conductivity state (diode closed). When a forward voltage is applied, a significant forward current arises, which leads to the accumulation of minority charge carriers in the base region (this is a high-resistance n - region). When a diode switches from the forward direction to the reverse direction, at the initial moment a large reverse current flows through the diode, limited mainly by the volumetric resistance of the base. Over time, the minority carriers accumulated in the base recombine or escape through the pn junction, and the reverse current decreases to its steady-state value. This entire process takes the recovery time of the reverse resistance tgoc - the time interval from the moment the current passes through zero after switching the diode until the reverse current reaches a specified low value. This is one of the main parameters of pulsed diodes, and according to its value they are divided into six groups: tboc >500 ns; tboc =150…500 ns; tboc =30…150 ns, tboc =5…30 ns; tboc =1…5 ns and tboc<1 нс.

Figure 1.11 - The process of switching a diode from open to closed state

When a current pulse is passed in the forward direction, a voltage surge is observed at the first moment after switching on (Figure 1.12), which is associated with an increase in voltage until the accumulation of minority carriers in the diode base ends. After this, the base resistance decreases and the voltage decreases.

Figure 1.12 The process of switching a diode from closed to open state

The values of these parameters depend on the structure of the diode and on the lifetime of minority charge carriers in the diode base. To reduce the lifetime of minority carriers, a small amount of gold impurity is introduced into the base. Gold atoms serve as additional recombination centers; as a result of their introduction, the lifetime of charge carriers and, consequently, the diffusion capacity of the pn junction decreases. Reducing the barrier capacity is achieved by technological and constructive methods. Pulse diodes are manufactured based on planar technology, epitaxial growth, and ion beam technology. The main semiconductor material in this case is silicon. In high-speed pulse circuits, Schottky diodes are widely used, in which the transition is made on the basis of a metal-semiconductor contact. The symbol is shown in Fig.

Figure - Schottky diode symbol

These diodes do not spend time accumulating and dissolving charges in the base; their performance depends only on the speed of the barrier capacitance recharging process. The current-voltage characteristic of Schottky diodes resembles the characteristic of diodes based on pn junctions. The difference is that the forward branch within 8 - 10 decades of applied voltage represents an almost ideal exponential curve, and the reverse currents are small (fractions to tens of nanoamperes). Structurally, Schottky diodes are made in the form of a low-resistance silicon wafer, on which a high-resistance epitaxial film with electrical conductivity of the same type is applied. A layer of metal is applied to the surface of the film by vacuum deposition. Schottky diodes are also used in high current rectifiers and logarithmic devices.

Pulse diodes.

This regular diodes, with a normal current-voltage characteristic, but operating in switching mode. Their field of application is digital circuits, the elements of which are either in the open state “0” or in the closed state “1”. Therefore, in this application, the timing parameters of the diode are of interest: how quickly it goes from off to on and vice versa. In Fig. shows a pulse diode based on an asymmetrical contact. Let us accept the condition that the emitter has n – conductivity. This gives grounds to consider the behavior and current of only electrons. With reverse asymmetry, everything said will apply to holes.

Let's consider the processes during switching. Let's apply direct voltage to it - an ideal stage, Fig. A). Initially, electrons with the highest energy, located directly near the p-n junction, will begin to move, then they will be joined by those located inside the n region. Thus, due to the difference in carrier energies, their number gradually increases, and the forward current gradually increases. This process over time is shown in Fig. b), and for evaluation, the parameter tset is introduced - the time to establish the open state. For a long time, the current does not change and a large number of minority carriers, electrons, accumulate in the “p” junction region. A nonequilibrium concentration of carriers arises in the p region of the crystal.

Let us apply an equally sharply changing reverse voltage polarity to the junction. Nonequilibrium electrons accumulated in the “p” region will begin to be removed under the influence of an electric field into the “n” region. Their concentration is high, so the reverse current will be large for some time. This stage of the process is shown in Fig. b) like t1. Eventually, the output process will end, the transition becomes a closed state. Now there are two semiconducting regions p and n b and a dielectric layer between them. This is a capacitor that begins to charge under the influence of reverse voltage. The charge current will decrease according to the exponential law, in Fig. b) this is time t2. In general, the recovery time of the closed state is equal to t1+t2=trestore.

Rice. Pulse diode

Rice. Processes in a pulsed diode.

Usually t restore

>> than t restore

A diode is one of the types of devices designed on a semiconductor basis. It has one p-n junction, as well as anode and cathode terminals. In most cases, it is designed for modulation, rectification, conversion and other actions with incoming electrical signals.

Principle of operation:

Electricity acts on the cathode, the heater begins to glow, and the electrode begins to emit electrons.
Between two electrodes an electric field is formed.
If the anode has a positive potential, then it begins to attract electrons to itself, and the resulting field is a catalyst this process. In this case, an emission current is generated.
Between electrodes a negative spatial charge is formed that can interfere with the movement of electrons. This happens if the anode potential is too weak. In this case, parts of the electrons fail to overcome the influence of the negative charge, and they begin to move in reverse direction, returning to the cathode again.
All electrons, which reached the anode and did not return to the cathode, determine the parameters of the cathode current. That's why this indicator directly depends on the positive anode potential.
Flow of all electrons, which were able to get to the anode, is called the anode current, the indicators of which in the diode always correspond to the parameters of the cathode current. Sometimes both indicators can be zero; this happens in situations where the anode has a negative charge. In this case, the field that arises between the electrodes does not accelerate the particles, but, on the contrary, slows them down and returns them to the cathode. The diode in this case remains in a locked state, which leads to an open circuit.

Device

Below is detailed description diode devices, studying this information is necessary for further understanding of the principles of operation of these elements:

Frame is a vacuum cylinder that can be made of glass, metal or durable ceramic varieties of material.
Inside the cylinder there are 2 electrodes. The first is a heated cathode, which is designed to ensure the process of electron emission. The simplest cathode in design is a filament with a small diameter, which heats up during operation, but today indirectly heated electrodes are more common. They are cylinders made of metal and have a special active layer capable of emitting electrons.
Inside the cathode indirect heat There is a specific element - a wire that glows under the influence of electric current, it is called a heater.
Second electrode is the anode, it is necessary to accept the electrons that were released by the cathode. To do this, it must have a potential that is positive relative to the second electrode. In most cases, the anode is also cylindrical.
Both electrodes vacuum devices are completely identical to the emitter and base of the semiconductor variety of elements.
For making a diode crystal Silicon or germanium is most often used. One of its parts is p-type electrically conductive and has a deficiency of electrons, which is formed artificial method. The opposite side of the crystal also has conductivity, but it is n-type and has an excess of electrons. There is a boundary between the two regions, which is called a p-n junction.

Such features of the internal structure give diodes their main property - the ability to conduct electric current in only one direction.

Purpose

Below are the main areas of application of diodes, from which their main purpose becomes clear:

Diode bridges are 4, 6 or 12 diodes connected to each other, their number depends on the type of circuit, which can be single-phase, three-phase half-bridge or three-phase full-bridge. They perform the functions of rectifiers; this option is most often used in car generators, since the introduction of such bridges, as well as the use of brush-collector units with them, made it possible to to a large extent downsize of this device and increase its reliability. If the connection is made in series and in one direction, this increases the minimum voltage required to unlock the entire diode bridge.
Diode detectors are obtained by combining these devices with capacitors. This is necessary so that it is possible to isolate the modulation from low frequencies from various modulated signals, including amplitude-modulated types of radio signals. Such detectors are part of the design of many household appliances, such as televisions or radios.
Ensuring protection of consumers from incorrect polarity when switching on circuit inputs from overloads or breakdown switches electromotive force, which occurs during self-induction, which occurs when an inductive load is turned off. To ensure the safety of circuits from overloads that occur, a chain is used consisting of several diodes connected to the supply buses in the reverse direction. In this case, the input to which protection is provided must be connected to the middle of this chain. During normal functioning circuit, all diodes are in a closed state, but if they have detected that the input potential has gone beyond the permissible voltage limits, one of the protective elements is activated. Due to this, this permissible potential is limited within the permissible supply voltage in combination with a direct drop in the voltage on the protective device.
Switches, created on the basis of diodes, are used to switch signals with high frequencies. Such a system is controlled using direct electric current, high-frequency separation and the supply of a control signal, which occurs due to inductance and capacitors.
Creation of diode spark protection. Shunt-diode barriers are used, which provide safety by limiting the voltage in the corresponding electrical circuit. In combination with them, current-limiting resistors are used, which are necessary to limit the electric current passing through the network and increase the degree of protection.

The use of diodes in electronics today is very widespread, since virtually no modern variety Electronic equipment cannot do without these elements.

Direct diode connection

The p-n junction of the diode can be affected by voltage supplied from external sources. Indicators such as magnitude and polarity will affect its behavior and the electrical current conducted through it.

Below we consider in detail the option in which the positive pole is connected to the p-type region, and the negative pole to the n-type region. In this case, direct switching will occur:

Under voltage from external source, an electric field will be formed in the p-n junction, and its direction will be opposite to the internal diffusion field.
Field voltage will decrease significantly, which will cause a sharp narrowing of the barrier layer.
Under the influence of these processes a significant number of electrons will be able to freely move from the p-region to the n-region, as well as in the opposite direction.
Drift current indicators during this process remain the same, since they directly depend only on the number of minority charged carriers located in the region of the pn junction.
Electrons have increased level diffusion, which leads to the injection of minority carriers. In other words, in the n-region there will be an increase in the number of holes, and in the p-region an increased concentration of electrons will be recorded.
Lack of equilibrium and increased number of minority carriers causes them to go deep into the semiconductor and mix with its structure, which ultimately leads to the destruction of its electrical neutrality properties.
Semiconductor at the same time, it is able to restore its neutral state, this occurs due to the receipt of charges from a connected external source, which contributes to the appearance of direct current in the external electrical circuit.

Diode reverse connection

Now we will consider another method of switching on, during which the polarity of the external source from which the voltage is transmitted changes:

The main difference from direct connection is that that the created electric field will have a direction that completely coincides with the direction of the internal diffusion field. Accordingly, the barrier layer will no longer narrow, but, on the contrary, expand.
Field located in the pn junction, will have an accelerating effect on whole line minority charge carriers, for this reason, the drift current indicators will remain unchanged. It will determine the parameters of the resulting current that passes through the pn junction.
As you grow reverse voltage, the electric current flowing through the junction will tend to reach maximum values. It has a special name - saturation current.
According to the exponential law, with a gradual increase in temperature, the saturation current indicators will also increase.

Forward and reverse voltage

The voltage that affects the diode is divided according to two criteria:

Forward voltage- this is when the diode opens and direct current begins to flow through it, while the resistance of the device is extremely low.
Reverse voltage- this is the one that has reverse polarity and ensures the closure of the diode with passage through it reverse current. At the same time, the resistance indicators of the device begin to increase sharply and significantly.

The resistance of a pn junction is a constantly changing indicator, primarily influenced by the forward voltage applied directly to the diode. If the voltage increases, then the junction resistance will decrease proportionally.

This leads to an increase in the parameters of the forward current passing through the diode. When this device is closed, virtually the entire voltage is applied to it, for this reason the reverse current passing through the diode is insignificant, and the transition resistance reaches peak parameters.

Diode operation and its current-voltage characteristics

The current-voltage characteristic of these devices is understood as a curved line that shows the dependence of the electric current flowing through the p-n junction on the volume and polarity of the voltage acting on it.

Such a graph can be described as follows:

Vertical axis: The upper area corresponds to the forward current values, the lower area to the reverse current parameters.
Horizontal axis: The area on the right is for forward voltage values; area on the left for reverse voltage parameters.
Direct branch of the current-voltage characteristic reflects the passage of electric current through the diode. It is directed upward and runs in close proximity to the vertical axis, since it represents the increase in forward electric current that occurs when the corresponding voltage increases.
Second (reverse) branch corresponds to and displays the closed state of the electrical current that also passes through the device. Its position is such that it runs virtually parallel to the horizontal axis. The steeper this branch approaches the vertical, the higher the rectifying capabilities of a particular diode.
According to the schedule you can see that after an increase in the forward voltage flowing through the p-n junction, a slow increase in electric current occurs. However, gradually, the curve reaches an area in which a jump is noticeable, after which an accelerated increase in its indicators occurs. This is due to the diode opening and conducting current at forward voltage. For devices made of germanium, this occurs at a voltage of 0.1V to 0.2V (maximum value 1V), and for silicon elements a higher value is required from 0.5V to 0.6V (maximum value 1.5V).
Current increase shown can lead to overheating of semiconductor molecules. If the heat removal that occurs due to natural processes and the operation of radiators is less than the level of its release, then the structure of the molecules can be destroyed, and this process will be irreversible. For this reason, it is necessary to limit the forward current parameters to prevent overheating of the semiconductor material. To do this, special resistors are added to the circuit, having serial connection with diodes.
Exploring the reverse branch you can notice that if the reverse voltage applied to the p-n junction begins to increase, then the increase in current parameters is virtually unnoticeable. However, in cases where the voltage reaches parameters exceeding the permissible norms, a sudden jump in the reverse current may occur, which will overheat the semiconductor and contribute to the subsequent breakdown of the p-n junction.

Basic diode faults

Sometimes devices of this type fail, this may occur due to natural depreciation and aging of these elements or for other reasons.

In total, there are 3 main types of common faults:

Transition breakdown leads to the fact that the diode, instead of a semiconductor device, becomes essentially the most common conductor. In this state, it loses its basic properties and begins to pass electric current in absolutely any direction. Such a breakdown is easily detected using a standard one, which starts beeping and showing low level resistance in the diode.
When broken the reverse process occurs - the device generally stops passing electric current in any direction, that is, it essentially becomes an insulator. To accurately determine a break, it is necessary to use testers with high-quality and serviceable probes, otherwise they can sometimes falsely diagnose this malfunction. In alloy semiconductor varieties, such a breakdown is extremely rare.
A leak, during which the tightness of the device body is broken, as a result of which it cannot function properly.

Breakdown of p-n junction

Such breakdowns occur in situations where the reverse electric current begins to suddenly and sharply increase, this happens due to the fact that the voltage of the corresponding type reaches unacceptable high values.

There are usually several types:

Thermal breakdowns, which are caused by a sharp increase in temperature and subsequent overheating.
Electrical breakdowns, arising under the influence of current on the transition.

The graph of the current-voltage characteristic allows you to visually study these processes and the difference between them.

Electrical breakdown

The consequences caused by electrical breakdowns are not irreversible, since they do not destroy the crystal itself. Therefore, with a gradual decrease in voltage, it is possible to restore all the properties and operating parameters of the diode.

At the same time, breakdowns of this type are divided into two types:

Tunnel breakdowns occur during the passage high voltage through narrow junctions, which makes it possible for individual electrons to slip through it. They usually occur if semiconductor molecules contain a large number of different impurities. During such a breakdown, the reverse current begins to increase sharply and rapidly, and the corresponding voltage is at a low level.
Avalanche types of breakdowns are possible due to the influence of strong fields capable of accelerating charge carriers to the maximum level, due to which they knock out a number of valence electrons from the atoms, which then fly into the conductive region. This phenomenon is of an avalanche nature, due to which this type breakdowns and received this name.

Thermal breakdown

The occurrence of such a breakdown can occur for two main reasons: insufficient heat removal and overheating of the p-n junction, which occurs due to the flow of electric current through it at too high rates.

Promotion temperature regime in the transition and neighboring areas causes the following consequences:

Growth of atomic vibrations, included in the crystal.
Hit electrons into the conduction band.
A sharp increase in temperature.
Destruction and deformation crystal structures.
Complete failure and breakdown of the entire radio component.

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Ministry of Education and Science of Ukraine

Dnepropetrovsk National University named after Oles Gonchar

Faculty of Physics, Electronics

and computer systems

Department of Radio Electronics

Test on “Solid-state electronics”

On the topic: “Features of a diode”

Completed

student of group KM-11-1

Mironenkov R.D.

Checked

Ph.D. physics and mathematics Sciences, Associate Professor of the Department of Radio Electronics.

Makarov V.A.

Dnepropetrovsk 2013

Essay

Key words: pulse diode, high-frequency diode, Gunn diode, current-voltage characteristic of the diode.

Purpose of the work: study of the characteristics and principles of operation of pulsed and high-frequency diodes

Introduction

1. Pulse diode. Operating principle

2. High frequency diode. Operating principle

2.1 Gunn diode

3. Manufacturing of diodes

Conclusion

Bibliography

Introduction

Semiconductors became a real goldmine of technology when they learned to make structures like layered cakes from them.

By growing an n-semiconductor layer on a p-semiconductor wafer, we obtain a two-layer semiconductor. The transition layer between them is called a pn junction. If you solder a connecting wire to each half, you will get a semiconductor diode that acts on the current like a valve: it passes current well in one direction, and almost not in the other direction.

How does the straightening barrier layer occur? The formation of a layer begins with the p-half having more holes and the n-half having more electrons. The difference in charge carrier density begins to balance through the transition: holes penetrate into the n-half, electrons into the p-half.

Using an external current source, you can increase or decrease the external potential barrier. If direct voltage is applied to the diode, that is, the positive pole is connected to the p-half, then the external electric force will begin to act against the double layer, and the diode passes a current that quickly increases with increasing voltage. If you change the polarity of the conductors, the voltage drops almost to zero. If a diode is connected to an alternating voltage circuit, it will serve as a rectifier, that is, the output will have a constant pulsating voltage in one direction (from plus to minus). In order to smooth out the amplitude, or as it is also called the “peak value,” of current ripple, it is effective to add a capacitor in parallel with the diode. Rectifier devices are quite often required in industry. For example, rectifiers are needed for proper operation household appliances (since almost all electrical appliances consume constant voltage. These are TVs, radios, VCRs, etc.). Semiconductor diodes are also needed to decipher video, radio, photos and other signals into frequency-electric signals. Using this property of semiconductors, we watch TV or listen to the radio.

There are also unusual semiconductor diodes - LEDs and photodiodes. Photodiodes pass current only when light hits their body. And LEDs, when current passes through them, begin to glow. The color of the LEDs depends on what type it belongs to.

Semiconductor diodes are divided into groups depending on their power, operating frequency range, voltage and operating frequency range. Both diodes and transistors have one unique property. When the temperature changes, they internal resistance changes and therefore the magnitude of the rectified current voltage also changes up or down. Light and photodiodes are used as sensors and indicators.

1. Pulse diode. Operating principle

These are ordinary diodes, with a normal current-voltage characteristic, but operating in switching mode. Their field of application is digital circuits, the elements of which are either in the open state “0” or in the closed state “1”. Therefore, in this application, the timing parameters of the diode are of interest: how quickly it goes from off to on and vice versa. Figure 1 shows a pulse diode based on an asymmetrical contact. Let us accept the condition that the emitter has n - conductivity. This gives grounds to consider the behavior and current of only electrons. With reverse asymmetry, everything said will apply to holes.

Fig.1. Pulse diode

Let's consider the processes during switching. Let's apply direct voltage to it - an ideal stage (Fig. 2.a). Initially, the electrons with the highest energy, located immediately near p-n junction, then they will be joined by those located inside the n region. Thus, due to the difference in carrier energies, their number gradually increases, and the forward current gradually increases. This process over time is shown in Fig. 2.b, and for evaluation, the parameter t mouth is introduced - the time to establish the open state. For a long time, the current does not change and a large number of minority carriers, electrons, accumulate in the “p” junction region. A nonequilibrium concentration of carriers arises in the p region of the crystal.

Let us apply an equally sharply changing reverse voltage polarity to the junction. Nonequilibrium electrons accumulated in the “p” region will begin to be removed under the influence of an electric field into the “n” region. Their concentration is high, so the reverse current will be large for some time. This stage of the process is shown in Fig. 2.b as t 1. Eventually, the output process will end, the transition becomes a closed state. Now there are two semiconducting regions p and n b and a dielectric layer between them. This is a capacitor that begins to charge under the influence of reverse voltage. The charge current will decrease according to the exponential law, in Fig. 2.b this is time t 2. In general, the recovery time of the closed state is equal to t 1 +t 2 =t recovery.

Fig.2. Processes in a pulse diode

Usually trest >> trest. To improve the parameters of the diode, materials with high carrier mobility (Ge) are used for manufacturing, the junction area is made small, and p-i-n structures are used. An example of using a pulse diode is shown in Fig. The voltage shape across the load resistance repeats the current shape in Fig. 3.

Fig. 3. Operation of a pulse diode

2. High frequency diodes. Operating principle

In ultrahigh frequency technology (for operation in the centimeter and millimeter wave ranges), special germanium and silicon ultrahigh frequency diodes (microwave diodes) are used. According to their purpose, microwave diodes are divided into video detector diodes, intended for detecting microwave oscillations, switching diodes, intended for use in microwave power level control devices, parametric ones, intended for use in parametric amplifiers of microwave oscillations, and converters. In turn, converter diodes that use the nonlinearity of the current-voltage characteristic of the transition are divided into:

· mixing devices used to convert a microwave signal and a local oscillator signal into an intermediate frequency signal;

· multipliers, used to multiply the frequency of the microwave signal;

· modulator, used to modulate the amplitude of the microwave signal.

Microwave diodes typically use a point contact. The junction in such diodes is not formed. The rectifying contact is made by simply pressing the tip of a metal contact spring against the polished surface of the semiconductor. These diodes are made of very low-resistance material (charge carrier lifetime is short) and have a very small point contact radius (2-3 µm), which provides good high-frequency properties. However, the breakdown voltage of microwave diodes is very low (only 3-5 V), and the forward voltage is relatively high.

Their reverse current, although small, begins to increase almost from zero due to the tunneling effect of carriers through the junction (Fig. 4).

Rice. 4. I-V characteristics of a high-frequency diode

The design of microwave diodes is usually adapted for coupling with elements of a coaxial or waveguide path, with measuring heads and other parts of the microwave system. In the long-wave section of the microwave range (3-10 cm), the main types of housing are metal-ceramic or metal-glass cartridge type. In the wavelength range of 1-3 cm, the dimensions and capacitance of these cases become unacceptably large, and therefore the rectifying contact is mounted in a coaxial type case. In the millimeter wave range, a waveguide design is used.

In addition to the wavelength at which microwave diodes have parameters guaranteed by standards terms of reference and maximum permissible data, microwave diodes are also characterized by electrical parameters that reflect the main value. Thus, mixing microwave diodes are characterized by conversion losses (the ratio of the microwave power at the input to the intermediate frequency power at the diode output), noise ratio (the ratio of the noise power at the diode output in operating mode to the thermal noise power of the active resistance of the diode), normalized noise factor characterizing the generalized sensitivity of the receiving device, and differential output impedance. In some cases, the electrical parameter determines not only the properties of the microwave diode itself, but also the properties of the specific microwave device in which this diode is installed.

It should be borne in mind that the power at which the diode “burns out,” accompanied by irreversible deterioration of the current-voltage characteristic or breakdown, is very small. Therefore, it is necessary to exclude any unintended influences and take the necessary protective measures both during operation and during storage of the microwave diode (for example, discharging static electricity accumulated on the operator’s body through the diode is unacceptable; storing the diode in a metal cartridge, etc.).

In millimeter-wave devices (especially integrated ones), avalanche diodes are widely used to build powerful microwave amplifiers, and Gunn diodes are widely used to build microwave generators. These diodes use the phenomenon of limiting electron mobility in electric fields with strengths above critical, and their current-voltage characteristics have a section with negative differential resistance. Avalanche diodes operate in the mode of avalanche multiplication of charge carriers with reverse bias of the electrical junction. Gunn diodes (there is no rectifying junction in the structure of these devices) use the effect of the occurrence of electrical oscillations in a gallium arsenide plate when a constant voltage is applied to it, creating an electric field with a strength of more than 105 V/m.

Industrially produced avalanche diodes and Gunn generators are designed for a continuous microwave output power of several tens of milliwatts. In pulsed mode, this power can be increased by several orders of magnitude. To increase the output power, avalanche diodes and Gunn generators with a larger area of the electron-hole junction and a larger area of the thin semiconductor film are needed. Moreover, they must be uniform not only in thickness, but also in area.

The operating frequencies of modern silicon microwave diodes are already approaching the theoretical limit. Therefore, in order to further improve the frequency properties, it is necessary to use a different material, as well as develop semiconductor devices with a different operating principle.

2.1 Gunn diode

Gunn diode (invented by John Gunn in 1963) is a type of semiconductor diode used to generate and convert oscillations in the microwave range at frequencies from 0.1 to 100 GHz. Unlike other types of diodes, the operating principle of a Gunn diode is not based on the properties of p-n junctions, i.e. all its properties are determined not by the effects that arise at the junction of two different semiconductors, but by the intrinsic properties of the semiconductor material used.

In the Russian literature, Gunn diodes were called devices with volume instability or with intervalley electron transfer, since active properties diodes are caused by the transition of electrons from the “central” energy valley to the “side”, where they can already be characterized by low mobility and large effective mass. In foreign literature, the Gunn diode corresponds to the term TED (Transferred Electron Device). high frequency pulse gunn diode

Based on the Gunn effect, generator and amplification diodes have been created, used as pump generators in parametric amplifiers, local oscillators in superheterodyne receivers, and generators in low power transmitters and in measuring technology.

When creating low-resistance ohmic contacts necessary for the operation of Gunn diodes, there are two approaches:

· The first of them is to search for an acceptable technology for depositing such contacts directly onto high-resistivity gallium arsenide.

· The second approach is to manufacture a multilayer generator structure. In diodes of this structure, epitaxial layers of relatively low-resistance gallium arsenide with n-type electrical conductivity are grown on both sides of a layer of relatively high-resistivity gallium arsenide, which serves as the working part of the generator. These highly alloyed layers serve as transition layers from the working part of the device to the metal electrodes.

A Gunn diode traditionally consists of a gallium arsenide layer with ohmic contacts on both sides. The active part of a Gunn diode usually has a length of the order of l = 1-100 μm and a concentration of donor dopant impurities n = 1014? 1016 cm?3. In this material in the conduction band there are two energy minima, which correspond to two states of electrons - “heavy” and “light”. In this regard, with increasing electric field strength, the average drift velocity of electrons increases until the field reaches a certain critical value, and then decreases, tending to saturation speed.

Thus, if a voltage is applied to the diode that exceeds the product of the critical field strength and the thickness of the gallium arsenide layer in the diode, the uniform distribution of voltage across the thickness of the layer becomes unstable. Then, if a slight increase in field strength occurs even in a thin region, the electrons located closer to the anode will “retreat” from this region towards it, and the electrons located at the cathode will try to “catch up” with the resulting double layer of charges moving towards the anode. When moving, the field strength in this layer will continuously increase, and outside it will decrease until it reaches an equilibrium value. Such a moving double layer of charges with a high electric field inside is called a strong field domain, and the voltage at which it occurs is called a threshold voltage.

At the moment of domain initiation, the current in the diode is maximum. As the domain is formed, it decreases and reaches its minimum at the end of formation. Reaching the anode, the domain is destroyed and the current increases again. But as soon as it reaches its maximum, a new domain. The frequency with which this process repeats is inversely proportional to the thickness of the semiconductor layer and is called the transit frequency.

On the current-voltage characteristic of a semiconductor device, the presence of a falling section is not a sufficient condition for the occurrence of microwave oscillations in it, but it is necessary. The presence of oscillations means that instability of wave disturbances occurs in the space of the semiconductor crystal. But such instability depends on the parameters of the semiconductor (doping profile, size, carrier concentration, etc.).

Fig.5. I-V characteristic of a Gunn diode

When placing a Gunn diode in a resonator, other generation modes are possible, in which the oscillation frequency can be made both lower and higher than the flight frequency. The efficiency of such a generator is relatively high, but the maximum power does not exceed 200-300 mW.

A Gunn diode can be used to create an oscillator in the 10 GHz and higher (THz) frequency range. And a resonator, which can take the form of a waveguide, is added to control the frequency. The frequency of Gunn diode oscillators is determined mainly by resonant frequency oscillatory system, taking into account the capacitive conductivity of the diode and can be tuned within a wide range by mechanical and electrical methods. However, the service life of Gunn generators is relatively short, which is due to the simultaneous impact on the semiconductor crystal of such factors as a strong electric field and overheating of the crystal due to the power released in it.

Gunn diodes operating in various modes, are used in the frequency range 1-100 GHz. In continuous mode, real generators based on Gunn diodes have an efficiency of about 2-4% and can provide output power from units of mW to units of W. But when switching to pulse mode, the efficiency increases by 2-3 times. Special resonant systems that make it possible to add some higher harmonics to the power of the useful output signal serve to increase efficiency and this mode is called relaxation.

There are several different modes, in one of which a Gunn diode generator can perform work, depending on the supply voltage, temperature, load properties: domain mode, hybrid mode, mode of limited accumulation of space charge and mode of negative conductivity.

The most commonly used mode is the domain mode, which is characterized by the existence of a dipole domain during a significant part of the oscillation period. Domain mode can have three various types: span, with a delay in the formation of domains and with suppression of domains, which are obtained when the load resistance changes.

For Gunn diodes, a mode of limiting and accumulating space charge was also invented and implemented. Its existence occurs at large voltage amplitudes at frequencies several times greater than the flight frequency and at constant voltages on the diode, which are several times higher than the threshold value. However, there are requirements for implementation to this regime: diodes with a very uniform doping profile are needed. Uniform distribution of the electric field and electron concentration along the length of the sample is ensured by high speed changes in voltage across the diode.

Along with gallium arsenide and indium phosphide InP (up to 170 GHz) using the epitaxial growth method, gallium nitride (GaN) is also used for the manufacture of Gunn diodes, on which the most high frequency oscillations in Gunn diodes - 3 THz. Gunn diode is low amplitude noise and low operating supply voltage (from units to tens of V).

The operation of diodes occurs in resonant chambers, which are in the form of microcircuits on dielectric substrates with resonating capacitive and inductive elements, or in the form of a combination of resonators with microcircuits.

3. Manufacturing of diodes

The diode manufacturing technology can be based on any of the methods described above for producing p-hc junctions on silicon and germanium. However, a device with the best amplifying qualities is obtained by diffusion, using mesa technology.

The manufacturing technology of Gunn diodes is relatively simple. Diodes are made either on the basis of single crystals or on the basis of epitaxial GaAs films. The dimensions of the plates for the manufacture of diodes are selected based on the conditions of their operating mode and the required parameters.

For the parameters and manufacturing technology of diodes and thyristors, the following abbreviations are used in the text and tables: Si - silicon, Qe - germanium, GaAs - gallium arsepide, CaP - gallium phosphite, Si(CO 3) 2 - silicon carbide.

Conclusion

In this work, we examined the operating principles of pulsed and high-frequency diodes. Each of the diodes has its own parameters, characteristics, and its purpose in the electrical circuit. Diode -- electronic element, having different conductivity depending on the direction of the electric current. The diode electrode connected to the positive pole of the current source when the diode is open (that is, has low resistance) is called anode, connected to the negative pole - the cathode.

Pulse diodes operate in the mode electronic key. The pulse duration can be very short, so the diode must transition from one state to another very quickly. The main parameter characterizing the performance of pulsed diodes is the recovery time of the reverse resistance. To reduce this, special measures are used that accelerate the process of resorption of minority charge carriers in the base. The requirements for pulsed diodes are well met by diodes based on the Schottky barrier, which have very low inertia due to the absence of injection and accumulation of minority charge carriers in the base.

The high-frequency diode is used for linear or nonlinear conversion of high-frequency signals up to 600 MHz. (Microwave diodes - up to 12 GHz.) It is used in detector circuits - these are rectifiers of high-frequency signals.

· Barrier capacitance Sat [µF]

f slave [MHz]

Modern imported diodes use such a characteristic as “Recovery time”. In ultra-fast diodes it reaches values of 100 ns.

Bibliography

1. Alferov Zh. I. // Physics and technology of semiconductors. 1998. T.32. No. 1. P.3-18.

2. Berg A., Dean P. LEDs / Transl. from English ed. A.E. Yunovich. M., 1979.

3. Kogan L. M. Semiconductor light-emitting diodes. M., 1983.

4. Losev O. V. At the origins of semiconductor technology: Selected works. L., 1972.

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