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Chapter 3 Lecture - Part 5

Thus lattice scattering dominates at high

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Unformatted text preview: e are 2 scattering mechanisms Recall • Lattice Scattering • Impurity Scattering – Lattice scattering is a result of temp dependent lattice Lattice vibrations and increase with increasing temperature. Thus lattice scattering dominates at high temperatures Thus – Impurity scattering is scattering from dopant atoms. and Impurity is not generally temperature sensitive. Heavy doping decreases mobility. decreases – Mobility goes as T3/2 for low temps and T-3/2 at high temps. temps. Mobility and Dopant Concentration Variation of mobility with total doping impurity concentration (Na + Nd ) for Ge, Si, and GaAs at 300 K. Mobility and Temperature Approximate temperature dependence of mobility with both lattice and impurity scattering. High E-field Effects in Semiconductors Saturation of electron drift velocity at high electric fields for Si. The Hall Effect The • Situation – Current flow in a SC is along the “long” axis – B field directed orthogonal to current flow • Governing equations: – – – F = q(E + v x B) Solving yields Fy = q(Ey – vxBz) Physically Fy = 0, so Ey = vxBz • Why Fy = 0? – The B field causes holes in the SC to shift along The the width the – A resulting Ey is set up (see above) as a result of charge separation charge The Hall Effect The – The charge shift will occur until Ey = vxBz and no more. more. – At this point the force on the e...
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