Ee 332 spring 2013 carrier motion in semiconductor

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Unformatted text preview: Spring 2013 Carrier Motion in Semiconductor •  Three primary types of carrier actions occur inside a semiconductor: ²་  Drift ²་  Diffusion ²་  Recombination-generation EE 332 Spring 2013 Thermal Motion Thermal Motion In thermal equilibrium, carriers are not sitting still: •  •  Undergo collisions with vibrating Si atoms (Brownian motion) Electrostatically interact with charged dopants and with each other Characteristic time constant of thermal motion – mean free time between collisions: In between collisions, carriers acquire high velocity: EE 332 Spring 2013 Thermal Velocity Thermal Velocity Thermal Velocity Average electron or hole kinetic energy EE 332 Spring 2013 arrier Scattering in Thermal Motion Carrier Scattering in Thermal Motion •  Mobile electrons and atoms in the Si lattice are always in random thermal motion Ø།  Electrons make frequent collisions with the vibrating atoms “Lattice scattering” or “photon scattering” Ø།  •  Other scattering mechanisms Ø།  Ø།  •  Average velocity of thermal motion for electrons: ~107 cm/s @300K Deflection by ionized impurity atoms Deflection due to Coulombic force between carriers (carrier-carrier scattering) The net current in any direction is zero, if no electric field is applied EE 332 Spring 2013 C Scattering Carrier arrier Scattering C Carrier Scattering •  Characteristic length of thermal motion: Calculate numbers for Si at 300 K: EE 332 Spring 2013 Carrier Motion in Electric Field Carrier Motion in Electric Field EE...
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This document was uploaded on 02/18/2014.

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