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1 1.56 10 Ω ∙ cm 8 J&B P2.50
Diffusion current density of holes is The concentration profile for holes is
10 10 cm Then
10
At 0, diffusion current density is 1.2 10 A/cm 0 1.2 10 A/cm Diffusion current is
0 0∙ 1.2 10 A 7 J&B P2.52
Note that the positive direction is to the right, and the direction of the electric
field is to the left, thus
20 V/cm. (The signs of , , , are very important
in this exercise!) The concentration profiles are linear, thus the gradients of
concentrations are
∆
∆ 5 10 cm ∆
∆ 5 10 cm
350 cm / V ∙ s , Mobilities of electrons and holes are
From Einstein’s relationship 150 cm / V ∙ s . The diffusivities of electrons and holes are (assuming room temperature,
25.9 )
9.1 cm /s
3.9 cm /s
At 0, 10 cm , 1.01 10 cm Electron diffusion current density:
72 A/cm
Hole diffusion current density:
31 A/cm
Electron drift current density:
11.2 A/cm
Hole drift current density: 4.85 10 A/cm Total current density:
5.4
1 m (midpoint) Since the profiles are linear, at
10 10
2 1.01 10
2 10 A/cm 5 10 10 cm
1.005 10 cm Electron and hole diffusion currents are the same as derived above:
72 A/cm
31 A/cm
Electron drift current density:
5.6 A/cm
Hole drift current density:
4.8 10 A/cm...
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 Fall '08
 Taicheng

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