The JFETs use a (reverse-biased pn junction, Schottky diode) as a gate to contro

Question

The JFETs use a (reverse-biased pn junction, Schottky diode) as a gate to control the (undepleted, depleted) part of a (source, channel, drain). At the (accumulation, flat-band, depletion) condition, there is no band bending as a function of depth in the channel. In a NMOSFET, a gate bias more (negative, positive) than flat-band voltage causes exponentially more (holes, electrons) to be accumulated with band bending. In a NMOSFET, above the threshold voltage, they attract (majority, minority) carrier near the surface forming a conductive channel. The V_T can be (increased, decreased) by increasing the channel doping. The V_T can be (increased, decreased) by increasing the oxide thickness. The dependence of I_D on V_G is approximately (quadratic, linear) for short channel devices.

Explanation / Answer

a) If a small negative voltage ( -VGS ) is applied to the Gate, the size of the depletion region begins to increase reducing the overall effective area of the channel and thus reducing the current flowing through it. So by applying a reverse bias voltage, we can increase the width of the depletion region which in turn reduces the conduction of the channel.

Answer: reverse-biased pn junction, undepleted, channel

b) Accumulation

c)

A MOS structure with a p-type semiconductor will enter the accumulation regime of operation when the voltage applied between the metal and the semiconductor is more negative than the flat-band voltage. In the opposite case, when V>VFB, the semiconductor – oxide interface first becomes depleted of holes and we enter the depletion regime. By increasing the applied voltage, the band bending becomes so large that the energy difference between the Fermi level and the bottom of the conduction band at the insulator – semiconductor interface becomes smaller than that between the Fermi level and the top of the valence band. Carrier statistics tells us that the electron concentration then will exceed the hole concentration near the interface and we enter the inversion regime.

Answer:positive, electrons

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