Lecture3 - 2 LECTURE3:CarrierAction;Definition EECS170A...

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10/23/2010 1 LECTURE 3: Carrier Action; Definition of Current and Its components EECS 170A 10/23/2010 1 10/23/2010 2 CURRENT CONDUCTION AND RESISTIVITY In previous lectures we answered on how current was created where we started with definition of current After all current means #of charges passing per second. Hence, in order to conduct electrical current we need to transport carriers from one location to other. Carriers can move around by the effect of two different mechanisms: Diffusion or electromagnetic field , that generate Diffusion and Drift currents ( ) F qE q v B Diffusion subject will be covered after the review of drift current . Let’s remember on Drift Current induced by electromagnetic field. We said that under constant electric field, E, and magnetic field B, the charged particle will expose to force F given by 10/23/2010 3 CURRENT CONDUCTION AND RESISTIVITY (2) Electrons are active carriers which move around randomly. However, the net displacement is 0 when there is no external force is present. External forces provide net displacement >0 In free space the motion of electron is uninterrupted In lattice the motion of electrons are interrupted by collisions E B * * * No magnetic field hol ) es ( where , are effective mass vales for electrons and n n p F qE dv F q m v E d q t B m m Random walk E=0 , 0 displacement Directional movement E 0 CURRENT CONDUCTION AND RESISTIVITY (3) What are these values at room temperature (it is temperature dependent!) 10/23/2010 4 * * 0 0 0 0 0 1.18 0.81 0.55 0.36 0.066 0.52 n p m m Si m m Ge m m GaAs m
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