Search results
Results From The WOW.Com Content Network
The electron–hole pair is the fundamental unit of generation and recombination in inorganic semiconductors, corresponding to an electron transitioning between the valence band and the conduction band where generation of an electron is a transition from the valence band to the conduction band and recombination leads to a reverse transition.
Semiconductors also can show several resonances well below the fundamental exciton resonance when phonon-assisted electron–hole recombination takes place. These processes are describable by three-particle correlations (or higher) where photon, electron–hole pair, and a lattice vibration, i.e., a phonon, become correlated.
Auger recombination is a similar Auger effect which occurs in semiconductors. An electron and electron hole (electron-hole pair) can recombine giving up their energy to an electron in the conduction band, increasing its energy. The reverse effect is known as impact ionization.
The same goes for a hole moving in the opposite direction. It is easiest to understand how a current is generated when considering electron-hole pairs that are created in the depletion zone, which is where there is a strong electric field. The electron is pushed by this field toward the n side and the hole toward the p side.
Once a photon has been absorbed and has generated an electron-hole pair, these charges must be separated and collected at the junction. A "good" material avoids charge recombination. Charge recombination causes a drop in the external quantum efficiency.
There are several mechanisms by which minority carriers can recombine, each of which subtract from the carrier lifetime. The main mechanisms that play a role in modern devices are band-to-band recombination and stimulated emission, which are forms of radiative recombination, and Shockley-Read-Hall (SRH), Auger, Langevin, and surface recombination, which are forms of non-radiative recombination.
The electron and hole bulk recombination lifetimes, and , in bulk GaAs are of the order of 10−8 s, about 2 orders of magnitude smaller than those in bulk silicon. Surface recombination reduces the power efficiency of the TPP effect as the electrons and holes recombine before they are collected at the contacts.
The small current that flows under high reverse bias is then the result of thermal generation of electron–hole pairs in the layer. The electrons then flow to the n terminal, and the holes to the p terminal. The concentrations of electrons and holes in the layer is so small that recombination there is negligible.