Lecture3-Carrier+Properties+and+Distribution_marked

Lecture3-Carrier+Properties+and+Distribution_marked - ECE...

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Unformatted text preview: ECE 3040 - Dr. Ying Zhang Georgia Tech ECE 3040: Microelectronic Circuits Lecture 3 Reading: Pierret 1.1, 1.2, 1.4, 2.1-2.6 ECE 3040 - Dr. Ying Zhang Georgia Tech Types of Materials: 1. Metals: high conductivity; narrow or no energy band gap 2. Insulators: low conductivity; wide energy band gap (5 eV in diamond, 8 eV in SiO 2 ) 3. Semiconductors: conductivity can be varied by several orders of magnitude under different conditions; an intermediate case between insulators and metals in terms of band gap (1.12 eV in Si, 0.66 eV in Ge, 1.42 eV in GaAs) 1) Elemental semiconductor 2) Compound semiconductor a) Binary (2 elements) b) Ternary (3 elements) c) Quaternary (4 elements) Control of conductivity is the Key to Modern Electronic Devices!!! Recapture ECE 3040 - Dr. Ying Zhang Georgia Tech Classification of electronic materials based on crystal structure: 1. Amorphous Materials 2. Polycrystalline Materials 3. Crystalline Materials Unit cell: a building block that can be periodically duplicated to result in the crystal lattice. Cubic lattices: three simple cubic unit cells Simple cubic unit cell Body-centered cubic cell (bcc) Face-centered cubic cell (fcc) Crystal structure for Si and many other semiconductor materials Diamond lattice unit cell Zincblende lattice unit cell Miller Indices Recapture ECE 3040 - Dr. Ying Zhang Georgia Tech Bohr Model 1. Electrons exist in stable, circular orbits around nucleus 2. Electrons can shift to orbits of higher or lower energy by photon absorption or emission 3. The energy of electrons in atomic systems is restricted to a limited set of values Two important models used in the analysis of semiconductor devices Bonding model Energy band model Conduction band Valence band Band gap Carriers Electrons: free electrons resides in the conduction band Holes: missing electrons found in the valence band Recapture ECE 3040 - Dr. Ying Zhang Georgia Tech Carrier Properties Intrinsic Material Extrinsic Material Density of States Fermi Level Equilibrium Distribution of Carriers Agenda ECE 3040 - Dr. Ying Zhang Georgia Tech Electrons and holes have equal and opposite charges (+/- q = 1.6 x 10-19 coul) Electron movement in free space under an electric field Newtons Second Law: This is only true in a vacuum, not in a crystal. In a crystal, we replace m with m* (Effective Mass). In a crystal, electrons are not totally free, and face a series periodic potentials caused by crystal lattice Electrons and holes are now treated as quasi-classical free particles Effective mass of electrons/holes in a crystal is a function of the material Carrier Properties mass electron m e ch electronic q time t velocity v force F dt dv m qE F o o = = , arg , , , E E ECE 3040 - Dr. Ying Zhang Georgia Tech mass effective electron m e ch electronic q time t velocity v force F dt dv m qE F n n = = * * , arg , , , mass effective hole m e ch electronic...
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Lecture3-Carrier+Properties+and+Distribution_marked - ECE...

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