ENGRI1110_Lect8_08 - Light Emitting Diodes Optoelectronic...

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Unformatted text preview: Light Emitting Diodes Optoelectronic device Solid-state analog of a light bulb Draws very little current p-n junction in a forward bias Light Emitting Diodes Creation of an electron-hole pair requires energy Electron-hole recombination releases energy photons (radiative) heat packets of (kinetic) energy localized regions of enhanced vibrations Radiative Recombination cnx.org/content/m1011 p-n junction in equilibrium (no bias) Why not Si? Wavelength of light emitted is not in the visible (it is part of the Infrared, IR) Band gap of Si is 1.1 eV Si is not efficient recombination energy can be released by non- radiative means Why not Si? Radiative recombination is slow because Si has an indirect band gap Electrons and holes have to wait for a suitable vibration to pass by before they can recombine radiatively This requirement is relaxed in disordered forms of Si Nanocrystalline Porous Silicon Sailor Group - UCSD Compound Semiconductors Crystal Structure Diamond C, Si, Ge GaAs Zinc blende Band Gap Comparisons 2.9 CuBr 2.7 SnSe 1.4 GaAs 0.7 Ge Eg Eg Compound Compound Band Gap Engineering (III-V) Band Gap scales with lattice constant III-V Semiconductors and Solid Solutions Lasers...
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ENGRI1110_Lect8_08 - Light Emitting Diodes Optoelectronic...

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