Semiconductor diodes are widely used in electronics and the electronics industry. They are used both independently and as a p-n-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 terminals". They are called anode and cathode. In a circuit, current flows from the anode to the cathode. The semiconductor diode is a one-sided element and current flow in the opposite direction is blocked.
Operation principle
The device of semiconductor diodes is very different. This is the reason that there are many types of them, which differ both in face value and in the functions they perform. However, in most cases the basic principleoperation of semiconductor diodes is the same. They contain a p-n junction, which provides their basic functionality.
This term is usually used in reference to the standard shape of a diode. In fact, it applies to almost any type of them. Diodes form the backbone of the modern electronics 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 is based on a group of materials, the introduction of impurities into the crystal lattice of which makes it possible to obtain regions in which holes and electrons are charge carriers.
P-n-junction
The p-n-type diode gets its name because it uses a p-n junction that allows current to flow in only one direction. The element has other properties that are also widely used. Semiconductor diodes, for example, can emit and detect light, change capacitance, and regulate voltage.
P-n-junction is a basic semiconductor structure. As the name suggests, it is a junction 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 current.
Standard diodes are usually made from silicon, although germanium and other semiconductor materials are also used, mainly for special purposes.
Volt-ampere characteristic
The diode is characterized by a current-voltage curve, which can be divided into 2 branches: forward 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 applied voltage above the conduction threshold, which is 0.7 V for silicon diodes and 0.4 V for germanium. Cells that use different materials have different volt-ampere characteristics and conduction threshold and breakdown voltages.
The p-n-junction diode can be considered as a basic level device. It is widely used in many applications ranging from signal circuits and detectors to limiters or transient suppressors in induction or relay coils and high power rectifiers.
Features and parameters
Diode specifications provide a lot of data. However, precise explanations of what they are are not always available. Below are the details of the various characteristics and parameters of the diode, which are given in the specifications.
Semiconductor material
The material used in p-n junctions is of paramount importance because it affects many of the fundamental characteristics of semiconductor diodes. Silicon is the most widely used because of its high efficiency and low production costs. Another frequently usedthe element is germanium. Other materials are typically used in special purpose diodes. The choice of semiconductor material is important because it determines the threshold of conduction - about 0.6 V for silicon and 0.3 V for germanium.
Voltage drop in direct current mode (U pr.)
Any electrical circuit through which current passes causes a voltage drop, and this parameter of a semiconductor diode is of great importance, especially for rectification, when power losses are proportional to U ave. In addition, electronic components often need to provide a small voltage drop, because the signals may be weak, but they still need to overcome it.
This happens for two reasons. The first lies in the very nature of the p-n junction and is the result of a conduction threshold voltage that allows current to cross the depletion layer. The second component is the normal resistive loss.
The indicator is of great importance for rectifier diodes, which can carry large currents.
Peak reverse voltage (U arr. max)
This is the highest reverse voltage that a semiconductor diode can withstand. It must not be exceeded, otherwise the element may fail. It's not just the RMS voltage of the input signal. Each circuit must be considered on its merits, but for a simple single half-wave rectifier with a smoothing capacitor, remember that the capacitor will hold a voltage equal to the peak of the inputsignal. The diode will then be subjected to the peak of the incoming signal in the reverse 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 pr. max)
When designing an electrical circuit, make sure that the maximum diode current levels are not exceeded. As the current 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 amount of leakage current depends on three factors. Obviously, the most significant of these is the reverse voltage. Also, the leakage current depends on 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.
Leakage current is determined at a certain reverse voltage and a certain temperature. It is usually specified in microamps (ΜA) or picoamps (pA).
Transition capacitance
All semiconductor diodes have junction capacitance. The depletion zone is a dielectric barrier between two plates that form at the edge of the depletion region and the region with the majority charge carriers. The actual capacitance value depends on the reverse voltage, which results in a change in the transition zone. Its increase expands the depletion zone and, consequently,reduces capacity. This fact is exploited in varactors or varicaps, but for other applications, especially RF applications, this effect must be minimized. The parameter is usually specified in pF at a given voltage. Special low-resistance diodes are available for many RF applications.
Case Type
Depending on the purpose, semiconductor diodes are produced in packages of various types and shapes. In some cases, especially when used in signal processing circuits, the package is a key element in determining the overall characteristics of that electronic element. In power circuits where heat dissipation is important, the package can determine many of the general parameters of a diode. High power devices need to be able to be attached to a heatsink. Small items can be produced in lead cases or as surface mount devices.
Types of diodes
Sometimes it is useful to get acquainted with the classification of semiconductor diodes. However, some items may belong to several categories.
Reversed diode. Although it is not as widely used, it is a type of p-n-type element, which in its action is very similar to the tunnel. Features low on-state voltage drop. Finds use in detectors, rectifiers and high frequency switches.
Injection transit diode. It has much in common with the more common avalanche-flying. Used in microwave generators and alarm systems.
Diode Gunn. It does not belong to the p-n-type, but is a semiconductor device with two terminals. It is commonly used to generate and convert microwave signals in the 1-100 GHz range.
Light emitting or LED is one of the most popular types of electronic components. In forward bias, the current flowing through the junction causes light to be emitted. They use compound semiconductors (e.g. gallium arsenide, gallium phosphide, indium phosphide) and can glow in a variety of colors, although they were originally limited to red only. There are many new developments that are changing the way displays function and are produced, OLED being an example.
Photodiode. Used to detect light. When a photon hits a p-n junction, it can create electrons and holes. Photodiodes typically operate under reverse bias conditions, where even small currents generated by 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 well describes the device of a semiconductor diode. It has standard p- and n-type regions, but there is an internal region without impurities between them. It has the effect of increasing the area of the depletion region, which can be useful for switching, as well as in photodiodes, etc.
Standard p-n-junction can be considered as a normalor the standard type of diode that is in use today. They can be used in RF or other low voltage applications, as well as high voltage and high power rectifiers.
Schottky diodes. They have a lower forward voltage drop than standard p-n-type silicon semiconductors. At low currents, it can be from 0.15 to 0.4 V, and not 0.6 V, as with silicon diodes. To do this, they are not made as usual - they use a metal-semiconductor contact. They are widely used as limiters, rectifiers and in radio equipment.
Diode with charge accumulation. It is a type of microwave diode used to generate and shape pulses at very high frequencies. Its operation is based on a very fast tripping characteristic.
Laser diode. It differs from ordinary light emitting as it produces coherent light. Laser diodes are used in many devices, from DVD and CD drives to laser pointers. They are much cheaper than other forms of lasers, but significantly more expensive than LEDs. They have a limited service life.
Tunnel diode. Although it is not widely used today, it was previously used in amplifiers, oscillators and switching devices, oscilloscope timing circuits, when it was more efficient than other elements.
Varactor or varicap. Used in many RF devices. For this diode, reverse bias changes the width of the depletion layer depending on the applied voltage. In this configuration itacts as a capacitor with a depletion region acting as an insulating dielectric and plates formed by the conductive regions. Used in voltage controlled oscillators and RF filters.
Zener diode. It is a very useful type of diode as it provides a stable reference voltage. Due to this, the zener diode is used in huge quantities. It works under reverse bias conditions 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. There are 2 types of reverse breakdown in zener diodes: Zener decomposition and impact ionization.
Thus, various types of semiconductor diodes include elements for low power and high power applications, emitting and detecting 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.
