Semiconductor diodes are widely used in electronics and the electronics industry. They are used both independently and as a pn junction of transistors and many other devices. As a discrete component, diodes are a key part of many electronic circuits. They find many applications, ranging from low-power applications to rectifiers.
What is a diode?
Translated from Greek, the name of this electronic element literally means "two conclusions." They are called the anode and cathode. In the circuit, current flows from the anode to the cathode. The semiconductor diode is a one-way element, and current flow in the opposite direction is blocked.
Operating principle
The device of semiconductor diodes is very different. This is the reason that there are many of their types, which differ both in nominal value and in the functions they perform. Nevertheless, in most cases, the basic principle of operation of semiconductor diodes is the same. They contain a pn junction, which provides their basic functionality.
This term is commonly used in relation to the standard form of a diode. In fact, it is applicable to almost any type. Diodes form the basis of modern electronic industry. Everything from simple elements and transistors to modern microprocessors is based on semiconductors. The principle of operation of a semiconductor diode is based on the properties of semiconductors. The technology relies on a group of materials whose introduction of impurities into the crystal lattice of which allows one to obtain regions in which holes and electrons are charge carriers.
Pn junction
The pn-type diode got its name because it uses the pn-junction, which allows the current to flow in only one direction. The element has other properties that are also widely used. Semiconductor diodes, for example, are able to emit and register light, change capacitance and regulate voltage.
The Pn junction is a basic semiconductor structure. As the name suggests, it is a compound between p- and n-type regions. The transition allows charge carriers to move in only one direction, which, for example, makes it possible to convert alternating current to direct.
Standard diodes are usually made of silicon, although germanium and other semiconductor materials are also used, mainly for special purposes.
Volt-ampere characteristics
The diode is characterized by a current-voltage curve, which can be divided into 2 branches: direct and reverse. In the opposite direction, the leakage current is close to 0, but with increasing voltage it slowly increases and when the breakdown voltage is reached, it begins to increase sharply. In the forward direction, the current rises rapidly with an increase in the applied voltage above the conductivity threshold, which is 0.7 V for silicon diodes and 0.4 V for germanium. Elements that use other materials have different current-voltage characteristics and conductivity threshold and breakdown voltages.
A diode with a pn junction can be considered as a basic level device. It is widely used in many applications, from signal circuits and detectors to limiters or transient suppressors in induction or relay coils and high power rectifiers.
Characteristics and parameters
Diode specifications provide a large amount of data. However, precise explanations of what they are are not always available. Below are detailed information on the various characteristics and parameters of the diode, which are given in the specifications.
Semiconductor material
The material used in pn junctions is of paramount importance because it affects many of the basic characteristics of semiconductor diodes. The most widely used silicon, because it is characterized by high efficiency and low production costs. Another frequently used element is germanium. Other materials are typically used in special purpose diodes. The choice of a semiconductor material is important because the conductivity threshold depends on it β about 0.6 V for silicon and 0.3 V for germanium.
Voltage drop in direct current mode (U ave.)
Any electric circuit through which current flows causes a voltage drop, and this parameter of the semiconductor diode is of great importance, especially for rectification, when the power loss is proportional to U etc. In addition, electronic elements often must provide a small voltage drop, since the signals can be weak but they still need to overcome it.
There are two reasons for this. The first is the very nature of the pn junction and is the result of a conductivity threshold voltage that allows the current to overcome the depletion layer. The second component is normal resistive losses.
The indicator is of great importance for rectifier diodes, through which large currents can pass.
Peak reverse voltage (U arr. Max)
This is the largest reverse voltage that a semiconductor diode can withstand. It must not be exceeded, otherwise the element may fail. This is not just the rms voltage of the incoming signal. Each circuit should be considered in essence, but for a simple rectifier with one half-wave with a smoothing capacitor, remember that the capacitor will hold the voltage equal to the peak of the input signal. Then the diode will be exposed to the peak of the incoming signal in the opposite direction, and therefore, under these conditions, there will be a maximum reverse voltage equal to the peak value of the wave.
Maximum forward current (U av. Max)
When designing an electrical circuit, make sure that the maximum current levels of the diode are not exceeded. As the amperage increases, additional heat is generated, which must be removed.
Leakage current (I arr.)
In an ideal diode, there should be no reverse current. But in real pn junctions, it is due to the presence of minority charge carriers in the semiconductor. The leakage current strength depends on three factors. Obviously, the most significant of these is reverse voltage. The leakage current also depends on the temperature - with its growth, it increases significantly. In addition, it is highly dependent on the type of semiconductor material. In this regard, silicon is much better than germanium.
The leakage current is determined at a specific reverse voltage and a specific temperature. It is usually indicated in microamps (ΞΌA) or picoamps (pA).
Junction capacity
All semiconductor diodes have junction capacitance. The depleted zone is a dielectric barrier between two plates that are formed on the edge of the depleted region and the region with the main charge carriers. The actual value of the capacitance depends on the reverse voltage, which leads to a change in the transition zone. Its increase expands the depletion zone and, therefore, reduces capacity. This fact is used in varactors or varicaps, but for other applications, especially radio frequency ones, this effect must be minimized. The parameter is usually indicated in pF at a given voltage. For many RF applications, special low-impedance diodes are available.
Type of shell
Depending on the purpose, semiconductor diodes are manufactured in housings of different types and shapes. In some cases, especially when used in signal processing circuits, the housing is a key element in determining the overall characteristics of this electronic element. In power circuits in which heat dissipation is important, the housing can determine many common diode parameters. High power devices need to be able to mount to a radiator. Small items can be manufactured in lead housings or as surface mount devices.
Types of diodes
Sometimes it is useful to familiarize yourself with the classification of semiconductor diodes. However, some items may fall into several categories.
Reversed Diode. Although it is not so widely used, it is a kind of pn-type element, which in its action is very similar to a tunnel one. It features a low voltage drop in the open state. It is used in detectors, rectifiers and high-frequency switches.
Injection-span diode. It has much in common with the more common avalanche-span. Used in microwave generators and alarm systems.
Gann diode. Not a pn type, but a two-pin semiconductor device. It is commonly used to generate and convert microwave signals in the range of 1-100 GHz.
Light emitting or LED is one of the most popular types of electronic elements. With forward bias, the current flowing through the junction causes light to be emitted. They use compound semiconductors (for example, gallium arsenide, gallium phosphide, indium phosphide), and they can glow in different colors, although initially they were limited only to red. There are many new developments that are changing the way the displays work and produce, for example OLED LEDs.
Photodiode Used to detect light. When a photon hits the pn junction, it can create electrons and holes. Photodiodes usually operate under reverse bias conditions, in which even a small current resulting from the action of light can be easily detected. Photodiodes can be used to generate electricity. Sometimes pin-type elements are used as photodetectors.
Pin diode. The name of the electronic element describes the semiconductor diode device well. It has standard p- and n-type regions, but between them there is an inner region without impurities. It has the effect of increasing the area of ββthe depletion region, which can be useful for switching, as well as in photodiodes, etc.
The standard pn junction can be considered as the usual or standard type of diode that is used today. They can be used in radio-frequency or other low-voltage devices, as well as in high-voltage and high-power rectifiers.
Schottky diodes. They have a lower forward voltage drop than standard pn type silicon semiconductors. At low currents, it can be from 0.15 to 0.4 V, but not 0.6 V, like silicon diodes. For this, they are not manufactured as usual - they use a metal-semiconductor contact. They are widely used as limiters, rectifiers and in radio equipment.
Battery diode. It is a type of microwave diode used to generate and generate pulses at very high frequencies. His work is based on a very fast shutdown characteristic.
Laser diode Differs from ordinary light emitting because it produces coherent light. Laser diodes are used in many devices - from DVDs and CD drives to laser pointers. They are much cheaper than other forms of lasers, but much more expensive than LEDs. Differ in the limited term of operation.
Tunnel diode. Although it is not widely used today, it was previously used in amplifiers, generators and switching devices, oscilloscope synchronization circuits, when it was more effective than other elements.
Varactor or varicap. Used in many RF devices. For a given diode, reverse bias changes the width of the depletion layer depending on the applied voltage. In this configuration, it acts as a capacitor with a depletion region acting as an insulating dielectric and plates formed by conductive regions. It is used in voltage controlled oscillators and RF filters.
Zener diode It is a very useful type of diode because it provides a stable reference voltage. Due to this, the zener diode is used in huge quantities. It works under conditions of reverse bias and breaks through when a certain potential difference is reached. If the current is limited by a resistor, then this provides a stable voltage. Widely used to stabilize power supplies. In Zener diodes, there are 2 types of backward breakdown: Zener decomposition and impact ionization.
Thus, various types of semiconductor diodes include cells for low power and high power applications that emit and detect light, with low forward voltage drop and variable capacitance. In addition to this, there are a number of varieties that are used in microwave technology.