ENGRI_111_11_photonics2

ENGRI_111_11_photonics2 - ENGRI 111 ENGRI 111 Photonics -...

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Unformatted text preview: ENGRI 111 ENGRI 111 Photonics - II Direct and Indirect Band Gap Direct and Indirect Band Gap VB CB Direct Band-Gap Indirect Band-Gap VB CB Why not Si? Why not Si? Radiative recombination is slow because Si has an “indirect” band gap The momentum of the recombined electron-hole pair is different from the excited pair 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 Nanocrystalline Porous Silicon Sailor Group - UCSD Size/Properties Size/Properties Molecular Orbital: H Molecular Orbital: H 2 2 www.science.uwaterloo.ca/~cchieh/cact/c120/mo.html Molecular Orbital: H Molecular Orbital: H 2 2 www.science.uwaterloo.ca/~cchieh/cact/c120/mo.html Crystal Structure Crystal Structure Diamond C, Si, Ge GaAs Zinc blende Molecular Orbitals for CH Molecular Orbitals for CH 4 4 sp 3 hybridized orbitals...
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This note was uploaded on 02/10/2008 for the course ENGRI 1110 taught by Professor Giannelis during the Spring '07 term at Cornell.

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ENGRI_111_11_photonics2 - ENGRI 111 ENGRI 111 Photonics -...

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