There are many sca5ering mechanisms with dierent

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Unformatted text preview: e mass is being used in the calcula[on: •  The Density of States Effec[ve Mass (Silicon) is used to count carriers * ( mn )3/2 = 6( ml mt2 )1/2 = 6(0.98 mo × (0.19 mo )2 )1/2 * mn = 1.1mo •  The Conduc[vity Effec[ve Mass (Silicon) is used for calcula[ons involving carrier transport 1 1⎛ 1 2⎞ * = ⎜ + ⎟ so mn = 0.26 mo * mn 3 ⎝ ml mt ⎠ 10 Mobility Comments •  Examining the previous analysis, it can be seen that: vx µn = − Ex vx µp = Ex •  Mobility is thus a measure of the average velocity of the carrier per unit of electric field •  Alterna[vely, mobility is the propor[onality constant that relates carrier velocity to electric field •  Because mobility is related to sca5ering, it will be found that this is a complex topic. There are many sca5ering mechanisms with different temperature dependences. 11 Example: Intrinsic Silicon Assume uniform distribution of carriers: no diffusion J n = −qn vn = −qn(−µn Ex ) + - J p = qp v p = qp(µ p Ex ) ρL ρL L 1 = = A wt wt σ 1 ρ= σ R= ρ (Intrinsic Silicon ) = 1 1 = σ q(nµ n + pµ p ) 1 1.6 x10 −19 (1.5 × 1010 • 1350 + 1.5 × 1010 • 480 ) 1 = = 2.28 × 10 5 Ω − cm 4.39 × 10 −6 (Ω − cm )−1 = We know how to calculate n and p What about µ? 12 What Value Do I Use for Mobility?...
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