What is impact ionization in semiconductors?

Impact ionization in semiconductors refers to a phenomenon where energetic electrons collide with atoms in the lattice, resulting in the excitation of electrons from their bounds to the conduction band, thereby generating additional free electrons. This occurs when an electron gains enough energy, typically from an applied electric field, such that when it collides with a lattice atom, it can impart sufficient energy to other electrons, liberating them.

As a result of this process, the number of charge carriers (electrons) in the semiconductor increases, which can significantly enhance its conductivity. This mechanism is crucial in devices like avalanche photodiodes and impact ionization avalanche transit time (IAATT) diodes, where controlled breakdown of the semiconductor can lead to a desirable increase in current flow.

In contrast, the other options do not accurately describe the concept. While jumping to another energy level may refer to band transitions, it does not capture the essence of impact ionization. Decreasing conductivity would instead involve mechanisms that reduce charge carrier density, while increasing temperature does not define the impact ionization process, as it pertains to electron behavior rather than thermal effects.