Conversely, in a p-channel 'enhancement-mode' device, a conductive region does not exist and negative voltage must be used to generate a conduction channel. P-channel In a p-channel 'depletion-mode' device, a positive voltage from gate to body widens the depletion layer by forcing electrons to the gate-insulator/semiconductor interface, leaving exposed a carrier-free region of immobile, positively charged acceptor ions. Further gate-to-source voltage increase will attract even more electrons towards the gate which are able to create a conductive channel from source to drain this process is called inversion. But first, enough electrons must be attracted near the gate to counter the dopant ions added to the body of the FET this forms a region with no mobile carriers called a, and the voltage at which this occurs is referred to as the of the FET. The positive voltage attracts free-floating electrons within the body towards the gate, forming a conductive channel. N-channel In an n-channel 'depletion-mode' device, a negative gate-to-source voltage causes a to expand in width and encroach on the channel from the sides, narrowing the channel. (For simplicity, this discussion assumes that the body and source are connected.) This conductive channel is the 'stream' through which electrons flow from source to drain. FET conventional symbol types The FET controls the flow of (or ) from the source to drain by affecting the size and shape of a 'conductive channel' created and influenced by voltage (or lack of voltage) applied across the gate and source terminals. The body terminal and the source terminal are sometimes connected together since the source is often connected to the highest or lowest voltage within the circuit, although there are several uses of FETs which do not have such a configuration, such as transmission gates and circuits. Usually the body terminal is connected to the highest or lowest voltage within the circuit, depending on the type of the FET.
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