Chapter 3 Lecture - Part 5

Electron figure 319 compensation in an n type

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Unformatted text preview: ; Ea – EF > Ei , so hole concentration in VB not balanced by electron concentration in Ea. electron Figure 3—19 Compensation in an n-type semiconductor (Nd > Na ). Carrier Concentrations Carrier Compensation • So how does Ea get filled if not from VB? – Initially Ea is filled by EHP generation in VB – Holes in VB are then filled by recombination with Holes electrons in CB not in Ea. electrons – This leads to a reduction in electrons in the conduction This band which might not be filled by electrons from the donor (if the donor has no more to give). donor – Electron concentration in CB is no longer Nd but Nd-Na • In compensated material, Na = Nd and conduction looks intrinsic (as if no dopants present!) looks Carrier Concentrations Carrier Space-Charge Neutrality • Describes the relationship between concentrations of Describes electrons, holes, donors and acceptors with respect to charge. to • In general for a charge neutral material: p0 + Nd+ = n0 + Nawhere Nd+ and Na- are fully ionized dopant concentrations. concentrations. or n0 = p0 + Nd+ - Na• For n-type material, n0 >>> p0 >>> Drift of Carriers in B and E Fields Drift Introduction • To calculate current, we need to know carrier To concentrations and account for collisions of electrons and holes with: electrons – lattice – impurities • Mobility: The ease at which electrons and holes Mobility: flow thru the crystal flow ...
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This note was uploaded on 04/02/2014 for the course EECS 321 taught by Professor Zorman during the Spring '10 term at Case Western.

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