NNSE618-L15-absorption

NNSE618-L15-absorpti - 1 Lecture contents Burstein shift Excitons Interband transitions in quantum wells Quantum confined Stark effect NNSE 618

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NNSE 618 Lecture #15 1 Lecture contents Burstein shift Excitons Interband transitions in quantum wells Quantum confined Stark effect
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NNSE 618 Lecture #15 2 Absorption edges in semiconductors Offset corresponds to bandgap Abs. coefficient is orders of magnitude higher for direct transitions Abs. coefficient roughly follows density of states
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NNSE 618 Lecture #15 3 Burstein-Moss shift Shift of absorption edge in degenerate semiconductors Usually in direct n-type semiconductors with low effective mass Due to occupation of band energy states up to: , the edge shifts: From Seeger, 1973 Absorption edge shift in doped n-InSb Burstein edge in degenerate n-type semiconductor e B n e T k m k 4 2 * 2 2 * * 2 2 1 1 2 h e g m m k E
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Lecture #15 4 Wannier Excitons r e r V i 2 ) ( Similar to hydrogen-like impurity: electron and hole bound by screened coulomb interaction Solution for discrete energy levels: With reduced effective mass (electron and hole orbiting around their center of mass): Envelope function of the ground state (hydrogen-like): Bohr radius: Free exciton can move in the crystal as a quasiparticle with a mass   B B a r a r F exp 1 ) ( 2 1 3 0 2 0 2 m e m a B 2 2 2 2 2 4 1 1 1 2 n m Ry n e E ex h e m m M
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This note was uploaded on 11/07/2011 for the course NNSE 618 taught by Professor Sergeoktyabrsky during the Spring '11 term at SUNY Albany.

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NNSE618-L15-absorpti - 1 Lecture contents Burstein shift Excitons Interband transitions in quantum wells Quantum confined Stark effect NNSE 618

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