Thank you sir

Dear S Jagan,

Adding to the colleague Martin, one speaks of recombination rate what is the rate of the disappearance of the excess electrons and holes in a semiconductor. As a measure of the recombination rate one defines the minority carrier lifetime Tau which is expressed by recombination rate = dp/ dt = delta p /Tau, where delta p is the excess minority holes in a p-type material. The minority carrier life time depends on the presence of electronic states in the energy gap acting as a recombination centers. As the density of the recombination centers increases the lifetime decreases. Crystallographic defects and deep lying impurities can act as effective recombination centers. There are also additional recombination mechanisms not involving the presence of recombination centers these are the band to band radiative recombination mechanism and the Auger recombination mechanism. The radiative recombination mechanism is appreciable in the direct gap materials where the Auger recombination appears at high carrier concentration.

It is clear from the foregoing introduction that the life time is variable and not a constant depending the factors mentioned above. It is said that it is a technological parameter. It could be increase by a process called gettering and decreased by doping of deep lying impurities and formation of crystallographic defects such as as ion implantation or electron irradiation.

For more information please follow the book in the link:Book Electronic Devices

You can follow also the discussion about the generation and recombination of carriers in semiconductors at the link:https://www.researchgate.net/post/Generation_recombination_of_electron_hole_pairs_in_semiconductors

Best wishes

Thank you sir.

The influence of particle or gamma-ray irradiation on the minority carrier lifetime in silicon (and other semiconductors) has a very practical meaning, as semiconductor devices are exposed to radiation in space and nuclear energy applications. In these cases, the reduction of the lifetime has a negative impact on the device performance with all the consequences, e.g., for space missions and telecommunications satellites. However, the reduction of the carrier lifetime in the base of silicon diodes and transitors by electron (gamma, proton) irradiation permits the fabrication of high-frequency devices. First, wafers with formed device structures are irradiated to a relatively high fluence (so that the lifetime drops down to a few ns) and then partially annealed in order to remove thermally unstable radiation defects and to tune the device parameters. It is a widely adopted technology.