Here's a more detailed explanation of the process of quantum avalanche:
1. High Electric Field: When a sufficiently high electric field is applied across a nonconductor or a semiconductor, the energy bands within the material are distorted and the bandgap between the valence band and the conduction band is reduced.
2. Electron Tunneling: Under the influence of the strong electric field, electrons from the valence band can overcome the reduced bandgap and tunnel through the energy barrier into the conduction band. This process requires less energy compared to the thermal excitation of electrons, which is the usual way electrons jump across the bandgap.
3. Carrier Multiplication: The electrons that tunnel into the conduction band gain energy from the electric field and accelerate, colliding with other valence electrons. These collisions cause further ionization and the generation of additional electron-hole pairs. This process is known as impact ionization or carrier multiplication.
4. Avalanche Effect: The newly generated electrons and holes can repeat the process of impact ionization, leading to a chain reaction-like effect where the number of charge carriers increases exponentially. This rapidly amplifies the electric current, causing the material to undergo a sudden transition from a nonconducting to a conducting state.
5. Plasma Formation: As the density of charge carriers continues to increase, the material's electrical resistivity decreases, and it starts to behave like a plasma. In this plasma state, a large number of free electrons and holes coexist, allowing the material to conduct electricity efficiently.
Quantum avalanche is a critical phenomenon in several electronic devices and applications, including avalanche photodiodes, photomultipliers, and high-power switches. It is also important in understanding the behavior of materials under extreme electric fields, such as lightning strikes or electrical breakdown in insulators.
