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Unformatted text preview: minority carrier concentrations. They lie within the
energy bands
energy Forwardbiased junction: (a) minority carrier distributions on the two sides of the transition region and
definitions of distances x n and xp measured from the transition region edges; (b) variation of the quasiFermi levels with position. Two methods for calculating junction current from the excess minority carrier distributions:
(a) diffusion currents at the edges of the transition region; (b) charge in the distributions divided by
the minority carrier lifetimes; (c) the diode equation. Currents and Forward Biasing
Currents
• Currents can be calculated in a number of ways:
– From the slopes of the excess minority carrier
From
distributions at the edges of the transition regions
distributions
– From the steady state charge (Q) in each region • Total current is the sum of the hole current
Total
injected into the n region [Ip(xn0)] and the electron
injected
)]
current injected into the p region [In(xpo)]
current
– This is valid if no recombination occurs in the
This
transition region as charges move across it.
transition • Since the total current in the pn device is
Since
constant throughout the structure, the current at
the edges describes the current everywhere
the Currents and Forward Biasing
Currents
• The majority carrier component of the current
The
is simply the total current less the minority
carrier component
carrier
• Physical explanation of the relation between
Physical
minority carrier injection and current:
minority
– Electrons move towards the junction from deep in
Electrons
the ntype region to replenish those lost by
recombining with the excess hole concentration in
this region.
this
– Excess electrons make it to the ptype region by
Excess
traversing W (injection), thus maintaini...
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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
 ZORMAN

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