Reverse bias breakdown apr 2 stored charge diusion and

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Unformatted text preview: AR 5 Steady state carrier injec\on, diffusion length MAR 7 p- n junc\ons in equilibrium & contact poten\al MAR 10 p- n junc\on Fermi levels and space charge MAR 12 Con\nue p- n junc\on space charge MAR 14 NO CLASS (EOH) MAR 17 p- n junc\on current flow MAR 19 Carrier injec\on and the diode equa\on MAR 21 Minority and majority carrier currents 3/24- 3/28 Spring Break MAR 31 Reverse- bias breakdown APR 2 Stored charge, diffusion and junc\on capacitance APR 4 Photodiodes, I- V under illumina\on **Subject to Change** 5 Today’s Discussion •  •  •  •  Quasi Fermi Levels & Photoconduc\vity Begin Diffusion Assignments Topics for Next Lecture 6 Steady Illumina\on: Revisited r = α r np = α r (no + δ n )( po + δ p ) = α r [ nopo + noδ p + poδ n + δ nδ p ] no(K)+δn Ÿ༉ r = α r [ nopo + ( no + po )δ n + δ n 2 ] = g(T ) + gopt Recall: g(T ) = α r ni2 = α r n0 p0 so δn gop = α r ( n0 + p0 )δ n = τn and δ n = δ p = gopτ n gopt g(T) Ÿ༉ po(K)+δp What Happens to the Fermi Level? 8 Quasi- Fermi Level •  A variety of mechanisms can create excess carriers (electrons and holes) •  The carriers may or may not be created in equal numbers –  This depends upon the mechanism that created them •  Regardless of how they were created, the quan\ty of excess carriers can be described by integra\ng the density of states \mes the probability of occupancy •  The probability of occupancy is s\ll a Fermi distribu\on, but with a modified Fermi energy, the “Quasi- Fermi Energy” or “Quasi- Fermi Leve...
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