Chapter 8 found copper's mean free path using the Fermi velocity

PHYSICS · Subjective · Fermi University Physics · Thermal, Statistical & Complex Systems · Condensed Matter, Materials & Soft Matter · Semiconductor physics and devices

Condensed Matter Physics, Ch Homogeneous semiconductors: counting carriers, doping and mobility

Problem

v_F

, not a thermal speed, because copper's Fermi temperature is

T_F=81\,600\,\mathrm{K}

, far above any temperature the metal reaches. This chapter instead used a thermal speed

\sqrt{3k_BT/m^*}

for silicon's carriers. Using copper's

E_F=7.0\,\mathrm{eV}

and silicon's own doped example, where

\mu

sits

0.26\,\mathrm{eV}

below

E_c

, explain why the two chapters need two different kinds of speed, and support the explanation with a numeric comparison.

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