Question
Sun December 04, 2011 By: Jency Prabharan

Dear madam I am not able to understand electron hole combination and recombination terms. also how it works in photodiode and led.

Expert Reply
Mon December 05, 2011
In the solid state physics of semiconductors, carrier generation and recombination are processes by which mobile charge carriers (electrons and electron holes) are created and eliminated.
Carrier generation and recombination result from interaction between electrons and other carriers, either with the lattice of the material, or with optical photons. As the electron moves from one energy band to another, its gained or lost energy must take some other form, and the form of energy distinguishes various types of generation and recombination

During radiative recombination, a form of spontaneous emission, a photon is emitted with the wavelength corresponding to the energy released. This effect is the basis of LEDs. Because the photon carries relatively little momentum, radiative recombination is significant only in direct bandgap materials.

When photons are present in the material, they can either be absorbed, generating a pair of free carriers, or they can stimulate a recombination event, resulting in a generated photon with similar properties to the one responsible for the event. Absorption is the active process in photodiodes, solar cells, and other semiconductor photodetectors, while stimulated emission is responsible for laser action in laser diodes.

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