Zener breakdown occurs when the high electric field is created across the junction. Zener breakdown occurs in zener diodes because they have very thin depletion region. Understand the breakdown voltage of a zener diode what zener breakdown voltage, and how its applied to. These two phenomena are quite like a natural occurrence. The zener breakdown can be defined as the flow of electrons across the p kind material barrier of the valence band to the evenly filled ntype material conduction band. The schottky diode is a semiconductor also known as hot carrier diode.
Explain zener breakdown mechanism in zener diode with vi. Zener diode is a pn junction diode specially designed to operate in the reverse biased mode. The types of break down diodes include schottky diode, zener diode and avalanche diode. Those two phenomena are 1 zener breakdown and 2 avalanche breakdown. If the reversebias applied to a pn junction is increased, a point will reach when the junction breaks down and reverse current rises sharply to a value limited only by the external resistance connected in series. Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. The crucial difference between the zener and avalanche breakdown is the operating mechanism. The avalanche process occurs when carriers in the transition region are accelerated by the electric field to energies. The other differences between them are explained below in the comparison chart.
The zener effect is a type of electrical breakdown that occurs in a reversebiased pn junction when the electric field enables tunnelling of electrons from the valence to the conduction band of a semiconductor, leading to a large number of free minority carriers which. Quantum mechanical tunneling of carriers through the bandgap is the dominant breakdown mechanism for highly doped pn junctions. Breakdown region is the normal operating region for a zener diode. Zener diode and avalanche diode are terms often used interchangeably, with the former much more common. It has a particular voltage known as break down voltage, at which the diode breaks down while reverse biased. Hbd854 zener theory and design considerations handbook. Zener breakdown occurs in heavily doped junctions in which the transition from the p side to the n side is very abrupt. Zener breakdown and avalanche breakdown the avalanche breakdown and zener breakdown are two different mechanisms by which a pn junction breaks. On the other hand, avalanche breakdown occurs in the device due to the collision of electrons moving at high speed. Moreover, the zener breakdown voltage has a negative temperature coefficient meaning which the zener breakdown voltage reduces with the increase in the junction temperature. A zener diode is a special type of device designed to operate in the zener breakdown region. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. Breakdown mechanisms figure 3 depicts the extension of reverse biasing to the point where voltage breakdown occurs.
Both mechanisms result in the same behavior and do not require different circuitry. A zener diode is a silicon pn junction device that is designed for operation in. If a p and n region are heavily doped then the breakdown voltage can be reduced. In a zener diode either or both breakdown mechanisms may be present. The difference between zener and avalanche breakdown include the following. Both refer to breakdown of a diode under reverse bias. The breakdown voltage of a zener diode is set by carefully controlling the doping level during. The zener breakdown takes place in a very thin junction, i. A zener diode is a silicon pn junction device that is designed for operation in the reversebreakdown region. Zener breakdown occurs in zener diodes with zener voltage v z less than 6v. The zener diode working principles and its various. Zener breakdown occurs because of the high electric field whereas, the avalanche breakdown occurs because of the collision of free electrons with atoms.
Normal diodes comprise a pn junction that conducts in the forward direction, but blocks any reverse voltage applied across it. Two mechanisms for the primary breakdown of reversebiased pn junctions have been proposed. Electrical break down of any material say metal, conductor, semiconductor or even insulator can occur due to two different phenomena. Zener 1, which postulates a spontaneous disruption of covalent bonds among atoms located in the immediate vicinity of the junction as a consequence of the high field that exists there. The zener and avalanche breakdown both occur in diode under reverse bias. Instead of a straight line representing the cathode, the zener diode has a bent line that reminds you of the letter z for zener. Zener breakdown occurs in zener diodes with zener voltage vz less than 6v. As we increase the reverse voltage applied to the zener diode, these minority carriers tend to accelerated. Zener breakdown is the phenomena wherein the zener diode experiences reverse breakdown at a much lower voltage than a normal diode, which may breakdown in excess of 100 volts, depending on the type. Major difference between zener and avalanche breakdown. At low doping levels and higher voltages the avalanche mechanism dominates while at heavy doping levels and lower voltages. A junction that results in a wider depletion region and, thus, a lower field intensity will break down by the avalanche mechanism before a zener breakdown condition can be reached. When the doping is heavy, even the reverse voltage is low, the electric field at barrier will be so strong thus the electrons in the covalent bonds can break away from the bonds.
Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials. The analysis is identical to that of tunneling in a metalsemiconductor junction section 3. What is the difference between a zener diode and an. Basics currentvoltage characteristic of a zener diode with a breakdown voltage of 17 volt. Typically zener breakdown causes the diode junction to break down below 5v and will not damage the device unless there is no provision made to release the heat generated. The symbol for a zener diode is shown in below figure. It occurs in a reverse biased pn diode when the electric field enables tunneling of electrons from the valence.
Zener diodes are normal pn junction diodes operating in a reverse biased condition. In the reverse biased condition, the conduction will take place only due to the minority carriers. Zener diode avalanche and zener breakdown study buddy. If the breakdown occurs at higher voltages from a few volts to hundreds of volts, the mechanism is avalanche breakdown. Differnece between zener breakdown and avalanche breakdown. The emitterbase breakdown voltage of planar transistors. E additional electron energy comes from the electric field. The zener breakdowns voltage is comparatively lesser than the breakdown of an avalanche.
This paper gives the results of some calculations of the breakdown voltage of such junctions and includes breakdown by both the avalanche multiplication and zener mechanisms. Working of the zener diode is similar to a pn junction diode in forward biased condition, but the uniqueness lies in the fact that it can also conduct when it is connected in reverse bias above its threshold breakdown voltage. Both the zener and the avalanche breakdowns occur in the reverse biasing stage. Zener diode breakdown characteristics instrumentation tools.
Pdf zener effect is discussed focusing on the energyband theory of solids, especially on the twoband models. Due to this reason the simple diodes where avalanche breakdown occurs is not used in the applications and instead zener diode is used in the application circuits of breakdown diodes such as. In the zener breakdown mechanism, the electric field becomes as high as 10 7 vm in the depletion layer with only a small applied. In electronics, the zener effect employed most notably in the appropriately named zener diode is a type of electrical breakdown, discovered by clarence melvin zener. Understanding the differences between a zener diode and a junction diode is. Zener diode definition a zener diode is a type of diode that permits current to flow in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as zener knee voltage or zener voltage. Zener diodes acts like normal pn junction diodes under forward biased condition. Difference between zener breakdown and avalanche breakdown. Zener breakdown and zener characteristic electrical4u. Difference between avalanche and zener breakdown voltage. This was a bad thing before the whole avalanche breakdown, large current.
Although all pn junctions exhibit a voltage breakdown, it is important to know that there are two distinct voltage breakdown mechanisms. When forward biased voltage is applied to the zener diode it allows large amount of electric current and blocks only a. The diode breakdown will happen through one of the following two mechanism. Before entering into the comparison of the zener breakdown vs avalanche breakdown let. Zener diode breakdown characteristics engineering tutorial. To explain the mechanism of reverse conduction, one needs to visualize the phenomenon of avalanche breakdown. Difference between zener and avalanche breakdown with.
Basic diode electronics introduction to diodes the pn junction. In normal diodes, the breakdown voltage is very high and the diode gets damaged totally if a voltage above the breakdown diode is applied, but in zener diodes, the breakdown voltage is not as high and does not lead to permanent damage of the zener diode if the voltage is applied as the reverse voltage applied to the zener diode increases towards the. The avalanche breakdown occurs because of the ionisation of electrons and hole pairs whereas the zener diode occurs because of heavy doping. The iv curve for a diode showing avalanche and zener breakdown. The avalanche breakdown is observed in the zener diodes having v z having than 8 v. The first mechanism, called the zener effect, is operative at low voltages up to a few volts reverse bias. One is called zener breakdown and the other is called avalanche breakdown. Avalanche breakdown mechanism minimum additional electron energy required for ionization can be estimated using. If this reverse voltage exceeds a certain value, the junction breaks down, usually failing permanently in the process. When connected in parallel with a variable voltage source so that it is reverse biased, a zener diode conducts when the voltage reaches the diodes reverse breakdown voltage. The reverse breakdown region the phenomenon of zener breakdown is related to avalanche breakdown. Zener diodes when we first talked about practical diodes, it was mentioned that a parameter associated with the diode in the reverse bias region was the breakdown voltage, v br, also known as the peakinverse voltage piv. The breakdown is either due to the zener breakdown effect that occurs below 5.
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