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Chapter 5 Lecture - Part 3

They lie within the energy bands energy forward

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Unformatted text preview: minority carrier concentrations. They lie within the energy bands energy Forward-biased 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 p-n 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 n-type region to replenish those lost by recombining with the excess hole concentration in this region. this – Excess electrons make it to the p-type region by Excess traversing W (injection), thus maintaini...
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