BrookeECE51_02

BrookeECE51_02 - Chapter Goals Explore semiconductors and...

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Unformatted text preview: Chapter Goals Explore semiconductors and discover how engineers control semiconductor properties to build electronic devices. Characterize resistivity of insulators, semiconductors, and conductors. Develop covalent bond and energy band models for semiconductors. Understand band gap ernergy and intrinsic carrier concentration. Explore the behavior of electrons and holes in semiconductors. Discuss acceptor and donor impurities in semiconductors. Learn to control the electron and hole populations using impurity doping. Understand drift and diffusion currents in semiconductors. Explore low-field mobility and velocity saturation. Discuss the dependence of mobility on doping level. The Inventors of the Integrated Circuit Jack Kilby Andy Grove, Robert Noyce, and Gordon Moore with Intel 8080 layout. The Kilby Integrated Circuit Semiconductor die Active device Electrical contacts Solid-State Electronic Materials Electronic materials fall into three categories: Insulators Resistivity ( ) > 10 5 -cm Semiconductors 10-3 < < 10 5 -cm Conductors < 10-3 -cm Elememental semiconductors are formed from a single type of atom, typically Silicon. Compound semiconductors are formed from combinations of column III and V elements or columns II and VI. Germanium was used in many early devices. Silicon quickly replaced silicon due to its higher bandgap energy, lower cost, and is easily oxidized to form silicon-dioxide insulating layers. Semiconductor Materials (cont.) Semiconductor Bandgap Energy E G (eV) Carbon (diamond) 5.47 Silicon 1.12 Germanium 0.66 Tin 0.082 Gallium arsenide 1.42 Gallium nitride 3.49 Indium phosphide 1.35 Boron nitride 7.50 Silicon carbide 3.26 Cadmium selenide 1.70 Covalent Bond Model Silicon diamond lattice unit cell. Corner of diamond lattice showing four nearest neighbor bonding. View of crystal lattice along a crystallographic axis. Silicon Covalent Bond Model (cont.) Near absolute zero, all bonds are complete. Each Si atom contributes one electron to each of the four bond pairs. Increasing temperature adds energy to the system and breaks bonds in the lattice, generating electron-hole pairs. Intrinsic Carrier Concentration The density of carriers in a semiconductor as a function of temperature and material properties is: E G = semiconductor bandgap energy in eV (electron volts) k = Boltzmanns constant, 8.62 x 10-5 eV/K T = absolute termperature, K B = material-dependent parameter, 1.08 x 10 31 K-3 cm-6 n i 2 = BT 3 exp- E G kT cm-6 Intrinsic Carrier Concentration (cont.) Electron density is n (electrons/cm 3 ) and n i for intrinsic material n = n i ....
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This note was uploaded on 03/29/2009 for the course ECE 51 taught by Professor Martinbrooke during the Fall '08 term at Duke.

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BrookeECE51_02 - Chapter Goals Explore semiconductors and...

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