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concentration of excess electrons in this region. Currents and Forward Biasing
• What drives current flow (majority carriers) ?
– Near the junction
• Drift and diffusion, with drift dominating
• Inhomogeneities in carrier distribution set up a diffusion
component – Far from the junction
• Drift only
• Homogeneity of charge carriers in this region means no
diffusion Currents and Forward Biasing Electron and hole components of current in a forward-biased p-n junction. In this example, we have a higher
injected minority hole current on the n-side than electron current on the p side because we have a lower n
doping than p doping. Charge Depletion and Reverse Biasing
• From the minority carrier perspective:
Δpn ~ -pn which indicates that p(xn0) = 0 • Reverse biasing leads to a depletion of minority
carriers at the boundaries
– Called minority carrier extraction • Physical interpretation
– Minority carriers are initially swept across the junction
– These carriers are not replaced by diffusion of carriers
to the junction boundaries
to • The quasi-Fermi levels adjust to reflect depletion
– The levels will fall outside the bands The Reverse Biased Junction (a) minority carrier distributions near the reverse-biased junction; (b) variation of the quasi-Fermi levels. The Quasi-Fermi Levels
• Recall that the Fermi level is a construct to
represent the distribution of charge carriers wrt the
energy band structure in equilibrium
• Quasi Fermi levels are the equivalent for steady
state situations such as biasing
• The quasi-Fermi leve...
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This note was uploaded on 04/02/2014 for the course EECS 321 taught by Professor Zorman during the Spring '10 term at Case Western.
- Spring '10