Class4_Slides

Class4_Slides - Steve Cronin University of Southern...

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Unformatted text preview: Steve Cronin University of Southern California Electrical Engineering - Electrophysics Semiconductor Physics EE.506 Tight Binding Method (4) Tight Binding Method (Polyacetylene) 2 inequivalent C atoms 2D Graphite Real Space Reciprocal Space 2D Graphite Tight Binding Model Reading Band Diagrams (27) Silicon- Which bands are filled? Which are emtpy? - Where in the BZ are the electrons? The holes? - How many carrier pockets are there? - What is the shape of the Fermi surface? - What are the effective masses? - Are the carrier velocities high or low? - Where in the BZ is the threshold for optical transitions? m l =0.98 m t =0.19 Electrons: m lh =0.16 m hh =0.49 Holes: Silicon- Where in the BZ is the threshold for optical transitions? - At what photon energy does the optical threshold occur? - Does the threshold correspond to a direct bandgap or an indirect (phonon-assisted) transition? - At what photon energy do you expect strong absorption? GaAs L-point, m=0.062m e m =0.67 Electrons: m lh =0.082 m hh =0.45 Holes: - Where in the BZ are the electrons? The holes? - How many carrier pockets are there? - What is the shape of the Fermi surface? - Are the carrier velocities high or low? - Where in the BZ is the threshold for optical transitions? - At what photon energy does the optical threshold occur? - Does the threshold correspond to a direct bandgap or an indirect (phonon-assisted) transition?...
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Class4_Slides - Steve Cronin University of Southern...

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