ee3161 spring10 lecture note 6

fermi level constant va va must be dropped across the

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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...
View Full Document

Ask a homework question - tutors are online