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Unformatted text preview: 1 EE360 – Lecture 64 Carrier Concentrations and Carrier Action • Objective: Be able to calculate carrier concentrations and currents in semiconductor devices. • Questions to be Answered: – Review and examples: How do we calculate carrier concentrations in practice? – How and why do we calculate the Fermi level? – How does drift describe carrier motion? EE360 – Lecture 64 Carrier Distributions and Concentrations: Review n-type material (more electrons than holes) intrinsic material (equal number of electrons and holes) p-type material (more holes than electrons) Pierret, p. 47 Pierret, p. 49 2 EE360 – Lecture 64 Carrier Concentration: Direct Approach • Integrate carrier distribution over the conduction band to find n and over the valence band to find p Integral of cond. band carrier distribution Integral of val. band carrier distribution Integrate Integrate Carrier Distribution Pierret, p. 50 Pierret, p. 47 EE360 – Lecture 64 Carrier Concentration: Direct Approach • Definition: effective density of states (does not depend on E ) • Non-degenerate assumption: – If E C- E F ≥ 3 kT and E F- E C ≥ 3 kT, then we say the semiconductor is non-degenerate kT E E kT E E C C F F C e e E f / ) ( / ) ( 1 1 ) ( − − ≈ + = Pierret, p. 51 Pierret, p. 52 3...
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- Spring '08
- Electric charge, Condensed matter physics, carrier concentration, nondegenerate Pierret