ee3161 spring10 lecture note 6

All impurities are ionized no free carriers exist in

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Unformatted text preview: s make some approximations. The depletion approximation: Impurity concentration abruptly changes from NA to ND at x=0 (step junction). All impurities are ionized. No free carriers exist in depletion region. Entire voltage drop occurs across depletion region. EE3161 Semiconductor Devices Sang-Hyun Oh 12 UNIVERSITY OF MINNESOTA Depletion Approximations EE3161 Semiconductor Devices Sang-Hyun Oh 13 UNIVERSITY OF MINNESOTA Depletion Approximations EE3161 Semiconductor Devices Sang-Hyun Oh 14 UNIVERSITY OF MINNESOTA P-N Junction n(x) = ni e(EF −Ei (x))/kT Fermi level What is JN, total? In which direction? What is JN, diffusion? In which direction? What is JN, drift? In which direction? EE3161 Semiconductor Devices Sang-Hyun Oh 15 UNIVERSITY OF MINNESOTA P-N Junction n(x) = ni e(EF −Ei (x))/kT Fermi level Question: Express build-in energy qVbi using Ei,p, Ei,n, and EF q Vbi = (Ei,p − EF ) + (EF − Ei,n ) = Ei,p − Ei,n EE3161 Semiconductor Devices Sang-Hyun Oh 16 UNIVERSITY OF MINNESOTA Important Issues Charge in the depletion region E-field in the depletion region Potential drop across the depletion region Width of the depletion region Calculation for one-sided junctions EE3161 Semiconduc...
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