EEE 537 L9 Electronic 2

EEE 537 L9 Electronic 2 - Electronic States of...

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Electronic States of Semiconductors • Valence band: Top most, fully filled band at T=0 • Conduction band: Bottom most empty band at T=0 Vacuum level • Affinity: from vacuum level to the bottom of conduction band hy valence band can be filled up? Due to Pauli e χ k E Why valence band can be filled up? Due to Pauli principle: No more than one electron can occupy a non-degenerate state g E k • Electrons in a fully occupied valence band do not participate conduction nce promoted to conduction band using whatever • Once promoted to conduction band using whatever means, electrons can move and produce currents • A “hole” would be left in the valence band EEE537 Fall 2010 C.Z. Ning ECEE ASU What is the “hole” like? 1 cning@asu.edu
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Holes in Semiconductor + = = e i i k k 0 k •Total momentum in a filled valence band e i k k -k e i k k e i h •The remaining valence band misses one e h q e e q = = = ) ( 0 charge, or carries • A hole is a valence band with one missing electron: a.k.a a quasi-particle, or a collective excitation; EEE537 Fall 2010 C.Z. Ning ECEE ASU • It carries a positive charge e; • It carries a momentum e h k k r r = 2 cning@asu.edu
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Band Structures of Semiconductors EEE537 Fall 2010 C.Z. Ning ECEE ASU Indirect Bandgap Direct Bandgap 3 cning@asu.edu
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Parabolic Approximation and Non-parabolic Effects onsider conduction band near the minimum: Consider conduction band near the minimum: e.g., conduction band edge 2 2 Parabolic approximation k=k 0 * 2m
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EEE 537 L9 Electronic 2 - Electronic States of...

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