# ch11 - andDevices Topic11: Fall2007 Learning Objectives...

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Topic 11 : Electrical Conduction in Solids                       Fall 2007 ECE 3500 - Semiconductor Materials  and Devices

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Learning Objectives In this topic you will learn: How carriers move in the presence of an electric field. The concept of drift mobility and how it varies with  temperature and doping. How a Hall voltage is established across a  semiconductor when it has current flowing through it  in the presence of a magnetic field.  How carriers move by diffusion in a semiconductor. The equations for current density in the case of drift  and diffusion of charge carriers.
Charge Carrier Drift Electrons and holes  drift  under the influence of an applied  electric field .

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Thermal Equilibrium At  thermal equilibrium , an individual e - /h +  moves around the lattice with a random thermal motion. Although an individual charge carrier may be displaced from its initial position after
Applied Electric Field With an electric field applied, again individual e -  s/h +  s may be displaced form their original positions after time t. However, under the influence of an applied electric field a group of e s/h + s will drift through the semiconductor at a  constant   drift velocity.

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Carrier Drift Velocity Why do the charge carriers drift at a constant velocity  ? Balance between forces of  acceleration   due to applied electric field and  retardation   due to collisions with the lattice.
Acceleration of Charge Carriers due to Electric Field The force on a single e -  due to the application of an electric field E  = -qE.

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