recombinationgeneration

Recombination-generation refers to the processes by which electron-hole pairs are destroyed (recombined) or created (generated) in semiconductors. These processes are fundamental to the behavior of electronic and optoelectronic devices and arise from thermal energy, optical excitation, electric fields, and material defects.

Recombination mechanisms include radiative or band-to-band recombination, where an electron recombines with a hole and emits a photon; Shockley-Read-Hall (SRH) trap-assisted recombination, which occurs via defect states within the band gap; and Auger recombination, a three-carrier process that transfers energy to a third carrier. Each mechanism dominates under different material conditions, such as crystal quality, carrier density, and temperature. Recombination rates are typically expressed as R, with characteristic forms like radiative, SRH, and Auger terms that depend on carrier densities and material parameters.

Generation mechanisms describe how electron-hole pairs are created. Thermal generation occurs across the band gap due to finite temperature. Optical generation arises from photon absorption in devices like solar cells and photodetectors. In many devices, generation balances recombination in steady state, and specialized regions such as depletion zones can feature strong generation or recombination currents.

A common framework uses the carrier-rate equation dn/dt = G − R + diffusion terms, where G is the generation rate and R the recombination rate. In steady state, G = R. The detailed form of R determines carrier lifetimes, diffusion lengths, dark current, and noise. These factors influence device performance: in solar cells, recombination reduces voltage and efficiency; in light-emitting devices, radiative recombination enhances light output; in detectors, lifetimes affect response time.

See also: minority carrier lifetime, diffusion length, solar cell physics, LED efficiency, trap states.