Advanced MOS DevicesChapter 2: pn Junction DiodesCullen College of EngineeringDepartment of Electrical and Computer EngineeringDr. Len TrombettaSpring 2011Equilibrium Junction DiodeEcEvEFEnergyEiq (x)x = xnox = -xpo++++----ACMEBlue Pointing Arrows(Box of 25)Wile-E Coyote Theorem: It doesn’t matter how high or steep the cliff is; if Wile-E Coyote goes over the edge, he will fall.This theorem suggests that the drift current will be about the same in forward and reverse bias as it is at equilibrium. Only the diffusion current changes significantly.pn Junction Diode with Applied BiasEcEvEFxEix = xnox = -xpoq(Vo-Va)qVaPierret, Semiconductor Device Fundamentals, Addison-Wesley 1996Pierret, Semiconductor Device Fundamentals, Addison-Wesley 1996The forward and reverse bias regions are enhanced in the next slides.Pierret, Semiconductor Device Fundamentals, Addison-Wesley 1996“Roll-off” at high current is due to either series resistance or to high level injection effects.The smaller slope at low current is due to carrier recombination in the depletion region, which increases the total current.The gradual increase in current before breakdown is due to the increase in size of the depletion region, which allows more generation current.Tunnel Ohmic ContactEFtunnelingelectronn+
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