2.3 Carrier Transport

# 2.3 Carrier Transport - 2.3 Carrier Transport 2.3.1 Carrier...

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ECE3080, Chapter 2.3 1 May 28, 2007 ECE 3080: Chapter 2.3 – Device Fundamentals O. Brand, 1 of 19 2.3 Carrier Transport 2.3.1 Carrier Drift Drift Current Mobility Resistivity Band Structure under Applied Field 2.3.2 Carrier Diffusion Diffusion Current 2.3.3 Total Current Equations Anderson, Chapter 3.1-3.4, page 111-131 Pierret, Chapter 3.1-3.2, page 75-104 May 28, 2007 ECE 3080: Chapter 2.3 – Device Fundamentals O. Brand, 2 of 19 2.3.1 Carrier Drift Drift = Charged particle motion in response to an applied electric field • Macroscopic Definition: Carriers of a given type (electrons or holes) move along at a constant velocity, the drift velocity, parallel or antiparallel to the applied electric field Drift Current Densities [A/cm 2 ]: ! J p,drift = qp ! v d,p ! J n,drift = ! qn ! v d,n I = dQ dt = J A Anderson, Fig. 3.3

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ECE3080, Chapter 2.3 2 May 28, 2007 ECE 3080: Chapter 2.3 – Device Fundamentals O. Brand, 3 of 19 Carrier Drift • For small electric fields, the drift velocity is proportional to the applied electric field with the mobility µ as proportionality factor: • The mobility is the central parameter characterizing the carrier drift, resulting in the following current densities: v d,p = μ p ! v d,n = " μ n ! ! J p,drift = qp μ p ! ! ! J n,drift = qn μ n ! ! ! J drift = ! J n + ! J p = q μ n n p p " # \$ % ! ! May 28, 2007 ECE 3080: Chapter 2.3 – Device Fundamentals O. Brand, 4 of 19 Drift Velocity vs. Electric Field Room Temperature and Low Doping Anderson, Fig. 3.9 Slope is Mobility
ECE3080, Chapter 2.3

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2.3 Carrier Transport - 2.3 Carrier Transport 2.3.1 Carrier...

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