Avalanche diode negative resistance is generated solid microwave devices using semiconductor structure carrier impact ionization and the transit time of two physical effects.
PN junction one-way conductivity, resistivity is small, a large reverse resistance.
When the reverse voltage is increased to a certain value, reverse current suddenly increases. It is the reverse electrical breakdown. It points avalanche and Zener breakdown.
Avalanche breakdown PN junction reverse voltage is increased to a value, like an avalanche multiplication of carriers, as far and fast increase.
Take advantage of this feature is to make the crystal diode avalanche diode
Major domestic manufacturers have Haiou light OTRON brand.
Avalanche breakdown in the electric field, the carrier energy increases constantly collide with atoms in the crystal, so that a covalent bond is formed in the electron excitation of free electron - hole pairs. New carriers generated by the collision and free electron - hole pairs, which is a multiplier effect. 1 Health 2,2 Alive 4, the same increase as the avalanche of carriers.
Zener breakdown is completely different, at high reverse voltage, there is a strong electric field PN junction, which can directly destroy covalently bound electrons will be separated to form an electron - hole pair formed a large reverse current. Zener breakdown electric field strength required great!
Only in impurity concentration particularly large PN junction to do the job.
It is in the applied voltage can produce high-frequency oscillation of transistors. High-frequency oscillations generated works: the use of avalanche breakdown of the crystal injected carriers, because the wafer carrier transit will take some time, so its current lags the voltage, It is often used in the field of microwave oscillation circuit.