Lecture 9 - Recombination and Generation

Lecture 9 - Recombination and Generation - Recombination...

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1 EE360 - Lecture 9 Recombination and Generation • Objective: Be able to calculate carrier concentrations and currents in semiconductor devices. • Questions to be Answered: – How are electrons and holes “created” and “destroyed?” EE360 - Lecture 9 Recombination-Generation Recombination : the process by which electrons and holes are destroyed Generation : the process by which electrons and holes are created • Occur continuously in all semiconductors.
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2 EE360 - Lecture 9 Band-to-band recombination • An electron from the conduction band recombines with a hole from the valence band • The energy of the electron ( E G ) is releases as a photon • For example, in GaAs band-to-band recombination yields a photon with energy ~1.4eV which corresponds to a wavelength of ~880 nm (infrared) • BUT, for many semiconductors, such as silicon, another mechanism dominates Pierret p. 106 EE360 - Lecture 9 Band-to-band RG Demo/Example
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3 EE360 - Lecture 9 Optical Emission • The energy of the emitted photon ( E ) is approximately the band-gap energy. • For infrared we can use GaAs: E G = 1.42, λ ~850nm • For red light ( λ ~630nm) we need a bandgap of ~2eV (AlGaAs or AlGaInP) • For blue light ( λ ~450nm) we need ~2.8eV bandgap (InGaN) EE360 - Lecture 9 R-G Centers • R-G Centers: defects or impurities that introduce an energy level near the middle of the band gap • Do not act as a donor or acceptor, but instead as a trap for electrons and holes • RG Centers trap electrons and holes at one location • Electrons and holes recombine and release heat • Heat takes the form of crystal lattice vibrations, or phonons Pierret p. 106
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This note was uploaded on 04/20/2008 for the course EE 360 taught by Professor Hastings during the Spring '08 term at Kentucky.

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Lecture 9 - Recombination and Generation - Recombination...

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