Electronic Properties of Solids, lecture 1 (WS15/16) Conductivity is a valuable parameter to sort materials conductivity metals: free e- move through crystall high conductivity → metallic apperance (high reflectance) other cases: semiconductors, insulators I = U / R U = R I (Ohms law) Band structures Metal Semi-Metal Insulator Semiconductor Electrons in solids are in bands with finite number density of states - they replace atomic orbitals - we only diccuss electrons that take part in binding
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Electronic Properties Solids 2015 - uni-muenchen.de · Electronic Properties of Solids, lecture 1 (WS15/16) Conductivit y is a valuable p arameter to sort materials conductivity metals:
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Electronic Properties of Solids, lecture 1 (WS15/16)
Conductivity is a valuable parameter to sort materials
conductivity
metals: free e- move through crystall high conductivity → metallic apperance (high reflectance)
other cases: semiconductors, insulators
I = U / R
U = R I (Ohms law)
Band structures
Metal Semi-Metal
Insulator
Semiconductor
Electrons in solids are in bands with finite number density of states- they replace atomic orbitals- we only diccuss electrons that take part in binding
Doped semiconductors
Compensated or poisoned semiconductor (~intrinsic)
both still thermally activated, but level is chosento work at RT ( ca. 50 -100 meV)
InterpretationElectrons in solids are from a physical viewpoint waves in a periodic medium (rather than point chargesin a fluid)→ interference effects→ solids act as heat bath for T>0, collisions
Material properties: band structure
wave vector
Electrons as a wave in free space
Newton:
- quadratic relation because of mass
constant curvature → constant mass high curvature → low mass
Group velocity and the slope of the dispersion Dispersion relation in a periodic media ( t l)
Consequences of the lattice:1) Bragg reflection2) Periodicity of wave function