What happened to Depletion region when biasing is Off after applying reverse biasing?

Discussion in 'General Electronics Chat' started by usmansa1, Jan 13, 2018 at 4:54 AM.

  1. usmansa1

    Thread Starter New Member

    Jan 22, 2017
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    Hi All,

    I was studying Diodes and I came across the information that when the diode is reversed biased the depletion region is increased. Now the depletion region is composed of neutral atoms that are combined and some layer is formed that further halts the movements of electrons and holes. When the diode is forward biased the depletion region is shrinked and when the diode is reversed biased the depletion region is widened as more neutral atoms are created near the layer. This is perfectly understandable why this phenomena happened. The next thing is the diode required some voltage in order for the electrons to cross the depletion region after biasing. This voltage is 0.7 volts or nearly 1 volts in case of silicon. When the depletion region is widened obviously more voltage is required by electrons to cross the depletion region.

    So my question is that when the biasing is off (Electric source) what happened to the depletion region after reverse biasing which cause the depletion region to be widened, will it come back to the normal where it was initially and why and by which mechanism it will come back, or if it was not suppose to come back to the normal then it means that voltage required to cross the depletion region will be changed depending upon the thickness ?

    Most electronics book (Which I studied) mentioned the phenomena of forward and reversed biased and mention their change on the depletion region but didnt mention that when the biasing is off after applying the reverse or forward biasing then what would happened.
     
  2. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    3,953
    4,156
    There is no hysteresis in PN junctions at room temperatures but there is a decay time of stored charge. There is a small value of ‘junction transition capacitance’ across the reversed junction (off equilibrium) that stores energy internally. When the bias is off the junction depletion region width returns to the junction formation equilibrium state size at the recombination (move charges out, current discharging the capacitance) mobility speed of the device charge carriers when the external voltage is removed.
    http://transport.ece.illinois.edu/ece340f12-lectures/ece340lecture27-junccap.pdf

    Chapter:
    Junction Capacitance
     
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