ee3161 spring10 lecture note 6

# fermi level constant va va must be dropped across the

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Unformatted text preview: NA 2 ND NA qND 2 + xn = Vbi 2KS ￿0 ￿ + ND x2 = Vbi n 28 ￿2 UNIVERSITY OF MINNESOTA Solution for xn and xp xn = ￿ 2KS ￿0 NA Vbi q ND (NA + ND ) ￿ ￿1 / 2 ￿1 / 2 ND xn xp = = NA 2KS ￿0 ND Vbi q NA (NA + ND ) W, the total width of the depletion region, or depletion width, is: W ≡ xn + xp = EE3161 Semiconductor Devices Sang-Hyun Oh ￿ 2KS ￿0 (NA + ND ) Vbi q NA ND 29 ￿1 / 2 UNIVERSITY OF MINNESOTA Step Junction with VA≠0 Move up or down? ? Fermi level: Constant? +VA VA must be dropped across the depletion region. Net result: Replace Vbi by Vbi-VA. EE3161 Semiconductor Devices 30 UNIVERSITY OF MINNESOTA Sang-Hyun Oh Depletion Width 1. Determine Vbi from doping densities 2. ￿ 2K ￿0 NA + ND W= Vbi q NA ND 3. What if there’s a bias VA applied across the junction? W= ￿ 2K ￿0 NA + ND (Vbi − VA ) q NA ND EE3161 Semiconductor Devices Sang-Hyun Oh 31 UNIVERSITY OF MINNESOTA Step Junction with VA≠0 Qualitatively sketch how these curves change with 1) forward bias and 2) reverse bias. Indicate what will happen to xn, xp, Emax, Vbi. EE3161 Semiconductor Devices Sang-Hyun Oh 32 UNIVERSITY OF MINNESOTA Energy Band Diagram: Qualitative Equilibrium VA=0 EF Forward bias VA > 0...
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