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JFETs are sometimes referred to as depletion-mode devices, as they rely on the principle of a depletion region, which is devoid of majority charge carriers. The depletion region has to be closed to enable current to flow. JFETs can have an n-type or p-type channel. In the n-type, if the voltage applied to the gate is negative with respect to ...
The mode can be determined by the sign of the threshold voltage (gate voltage relative to source voltage at the point where an inversion layer just forms in the channel): for an N-type FET, enhancement-mode devices have positive thresholds, and depletion-mode devices have negative thresholds; for a P-type FET, enhancement-mode have negative ...
In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region, space charge region, or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have diffused away, or been forced away by an electric field. The only elements left ...
Cross-sectional view of a MOSFET type field-effect transistor, showing source, gate and drain terminals, and insulating oxide layer. The field-effect transistor (FET) is a type of transistor that uses an electric field to control the current through a semiconductor. It comes in two types: junction FET (JFET) and metal-oxide-semiconductor FET ...
With no V GS, dopant ions added to the body of the FET form a region with no mobile carriers called a depletion region. A positive V GS attracts free-floating electrons within the body towards the gate. But enough electrons must be attracted near the gate to counter the dopant ions and form a conductive channel. This process is called inversion.
Therefore the depletion region is necessary to allow for only one direction of current. The metal–oxide–semiconductor field-effect transistor (MOSFET) relies on band bending. When the transistor is in its so called 'off state' there is no voltage applied on the gate and the first p-n junction is reversed bias.
The active FET layer is usually deposited onto this substrate using either (i) thermal evaporation, (ii) coating from organic solution, or (iii) electrostatic lamination. The first two techniques result in polycrystalline active layers; they are much easier to produce, but result in relatively poor transistor performance.
The subthreshold slope is a feature of a MOSFET's current–voltage characteristic.. In the subthreshold region, the drain current behaviour—though being controlled by the gate terminal—is similar to the exponentially decreasing current of a forward biased diode.