The regions near the p n interface lose their neutrality and most of their mobile carriers, forming the space charge region or depletion layer ( see figure A ).
12.
CB may be more physically plausible, in agreement with the physical origin of the effect, which is a widening of the collector base depletion layer that depends on " V"
13.
In the threshold voltage page the definition is the voltage required to push all the majority carriers away from the gate creating a depletion layer ( at higher voltages the inversion layer forms ).
14.
But, in practice, surface impurities within the part of the semiconductor that touches the metal terminals will greatly reduce the width of those depletion layers to such an extent that the metal-semiconductor junctions do not act as diodes.
15.
Thus, field penetration is arrested when the exposed negative acceptor ion charge balances the positive charge placed on the insulator surface : the depletion layer adjusts its depth enough to make the net negative acceptor ion charge balance the positive charge on the gate.
16.
Because the valence band levels near the surface are fully occupied due to the lowering of these levels, only the immobile negative acceptor-ion charges are present near the surface, which becomes an electrically insulating region without holes ( the " depletion layer " ).
17.
In equilibrium, with no applied bias, thermally assisted diffusion of electrons and holes in opposite directions across the depletion layer ensure a zero net current with electrons flowing from cathode to anode and recombining, and holes flowing from anode to cathode across the junction or depletion layer and recombining.
18.
In equilibrium, with no applied bias, thermally assisted diffusion of electrons and holes in opposite directions across the depletion layer ensure a zero net current with electrons flowing from cathode to anode and recombining, and holes flowing from anode to cathode across the junction or depletion layer and recombining.
19.
Constriction of the conducting channel is accomplished using the field effect : a voltage between the gate and the source is applied to reverse bias the gate-source pn-junction, thereby widening the depletion layer of this junction ( see top figure ), encroaching upon the conducting channel and restricting its cross-sectional area.
20.
Barrier lowering increases as channel length is reduced, even at zero applied drain bias, because the source and drain form pn junctions with the body, and so have associated built-in depletion layers associated with them that become significant partners in charge balance at short channel lengths, even with no reverse bias applied to increase depletion widths.
