3.1自由电子的经典理论 德鲁得( Denude)理论的困难 n Temperature dependence of resistivity E E /e /e 0=一= ne ne lat ne T Metal Resistance increases with Temperature Why?↑emp→↓r, n same(same# conduction electrons)→↑p Semiconductor: Resistance decreases with Temperature Why?Temp→r,↑n(“ free-up carriers to conduct))→2 1 ( ) E d F ma E m e e J ne v ne a n ne ρ τ τ τ == = = ∝ • Metal: Resistance increases with Temperature. • Why? ↑Temp ⇒ ↓τ, n same (same # conduction electrons) ⇒ ↑ρ • Semiconductor: Resistance decreases with Temperature. • Why? ↑Temp ⇒ ↓τ, ↑n (“free-up” carriers to conduct) ⇒ ↓ρ ￾ Temperature dependence of resistivity. 3.1 自由电子的经典理论 德鲁得（Derude）理论的困难