Impact ionization is a process in semiconductors that usually is detrimental to circuit performance. It occurs in regions of very high electric field, such as the depletion region of a p-n junction or the pinchoff region of a MOSFET. The high electric field causes electrons to acquire kinetic energy greater than the bandgap. These high-energy carriers scatter with electrons in the valence band, causing them to jump to the conduction band, which creates an electron-hole pair.

The newly created current carriers are themselves accelerated by the electric field, and a chain reaction occurs. The exponential increase in free carriers results in runaway current. In a semiconductor diode, this breakdown mechanism is known as avalanche breakdown. Semiconductor materials are characterized by a critical breakdown field, defined as the field at which on average one carrier undergoes impact ionization upon travelling one micron.

Log in or registerto write something here or to contact authors.