Original title: diode breakdown
When using diodes, we often talk about the everse breakdown of diodes. This paper summarizes the concepts and terms of diode breakdown. What is the everse breakdown of diode? Crystal diode is a p-n junction formed by P-type semiconductor and N-type semiconductor, which forms space charge layers on both sides of its interface and establishes its own electric field. In the absence of an applied voltage, the diffusion current caused by the carrier concentration difference on both sides of the p-n junction is equal to the drift current caused by the construction electric field, which is in an electric balance state. When there is an external direct voltage shift, the mutual inhibition of external electric field and self-operated electric field increases the diffusion current of carriers and causes forward current. When the external voltage is biased, the external electric field and self-built electric field will be further strengthened, and the everse saturation current I0 will be formed in a certain everse voltage range, which is independent of the everse bias voltage value. When the added everse voltage is high to a certain extent, the electric field intensity in the space charge layer of the p-n junction reaches a critical value, resulting in the multiplication process of carriers, a large number of electron holes and a large everse breakdown current, which is called diode breakdown phenomenon.
How many breakdown modes do diodes have?
Diodes have two breakdown modes, which are zener breakdown and collapse.
What are the principles of Zener breakdown and avalanche breakdown?
Zener breakdown means that when the everse voltage increases to a certain value, a strong electric field can be established in the barrier region. It can directly pull out the price electrons bound in covalent bonds, causing a large number of electron holes in the barrier region. A large everse current is formed, causing damage. Under the action of strong electric field, the breakdown phenomenon directly stimulated by atoms in the barrier region is called Zener breakdown. Zener breakdown usually occurs in PN junction with high mixed concentration. This is because the PN junction with high mixing concentration has large charge density and narrow width in the space charge region, so long as the everse voltage is not increased, a strong electric field can be established and Zener breakdown can occur.
Avalanche breakdown refers to the enhancement of electric field in space charge region when the everse voltage of PN junction increases in PN junction with low material mixing concentration. In this way, through the electrons and holes in the space charge region, the energy obtained can be increased under the action of the electric field. Electrons and holes running in the body constantly collide with crystal atoms. Through this collision, the price electrons bound to covalent bonds collide to produce free electron-hole pairs. The newly generated carriers collide with other price electrons under the action of electric field. New pairs of free electrons and holes are generated. In this chain reaction, the number of carriers in the barrier layer increases avalanche, and the current flowing through the PN junction increases sharply. Collision ionization that destroys the PN junction is called avalanche destruction, also known as electron avalanche phenomenon.
What is the difference between Zener breakdown and avalanche breakdown?
Difference 1: Avalanche breakdown means that under the action of electric field, the energy of carriers increases and constantly collides with crystal atoms, so that electrons in covalent bonds are excited to form free electron-hole pairs. The newly generated carriers generate free electron-hole pairs by collision, which is called multiplication effect. 1 gives birth to 2, 2 gives birth to 4, increasing carriers like avalanche. Zener breakdown is different. Under high everse voltage, there is a strong electric field in PN junction, which can be directly destroyed! Covalent bonds separate bound electrons to form electron-hole pairs, resulting in large everse currents. The electric field intensity required by Zener breakdown is very high, which can only be achieved in PN junction with extremely high impurity concentration. (The charge density is higher when impurities are large.) The doping concentration of ordinary diodes is not so high, and their electrical breakdown is avalanche breakdown. Zener breakdown mostly occurs in a special diode, which is a zener diode. Both diodes work in everse breakdown region, and the difference between them lies in the ability to withstand transient impulse and the clamping voltage level. In lightning protection design, volt-ampere characteristics of two kinds of diodes are applied to suppress lightning overvoltage.
Difference 2: avalanche breakdown requires high voltage! Avalanche breakdown means that when the everse voltage of PN junction increases to a value, carrier multiplication increases much and quickly like avalanche. Zener breakdown is different, under high everse voltage
Can diode breakdown be utilized?
Some diodes are designed and manufactured by using the everse breakdown characteristics of diodes. For example, zener diode, also known as zener diode, uses the everse breakdown characteristic of diode to stabilize voltage. It is a semiconductor device with high resistance until the critical everse breakdown voltage. At this critical breakdown point, the everse resistance decreases to a very small value, and the current increases and the voltage remains constant in this low resistance region.
Avalanche diode is a transistor that can generate high frequency oscillation under the action of applied voltage. Avalanche breakdown is used to inject carriers into crystals. Because it takes a certain time for carriers to cross the wafer, their current lags behind the voltage, resulting in delay time. If the transit time is properly controlled, negative resistance effect will appear in the relationship between current and voltage, resulting in high-frequency oscillation.
What is thermal breakdown?
The essence of the thermal breakdown is the medium in the electric field, which generates heat due to the loss of the medium, that is, the potential energy is converted into heat. When the applied voltage is high enough, it may turn from the heat balance state of heat dissipation and heat generation into an unbalanced state. If the heat emitted is more than the heat dissipated, the temperature of the medium will become higher and higher until long-term damage occurs. This is the thermal breakdown.
The above mainly introduces the related contents of diode breakdown.
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Title: diode breakdown
