If the channel is doped with an acceptor impurity, p-type material will be formed and the channel current will consist of holes.If the channel is doped with a donor impurity, n-type material is formed and the channel current will consist of electrons.JFET is a high-input resistance device, while the BJT is comparatively low.The fundamental difference between JFET and BJT devices: when the JFET junction is reverse-biased the gate current is practically zero, whereas the base current of the BJT is always some value greater than zero.The magnitude of this current is controlled by a voltage applied to a gate, which is a reverse-biased.Conducting semiconductor channel between two ohmic contacts – source & drain.JFETs consists of a piece of high-resistivity semiconductor material (usually Si) which constitutes a channel for the majority carrier flow.The Field Effect Transistor (FET) The family of FET devices may be divided into : The term refers to the fact that current is transported by carriers of one polarity (majority), whereas in the conventional bipolar transistor carriers of both polarities (majority and minority) are involved.The FET was known as a “unipolar” transistor.Field-effect transistors are so named because a weak electrical signal coming in through one electrode creates an electrical field through the rest of the transistor.Field effect devices are those in which current is controlled by the action of an electron field, rather than carrier injection.By the late 1960s, manufacturers converted from junction type integrated circuits to field effect devices.In 1960 Bell scientist John Atalla developed a new design based on Shockley's original field-effect theories.Three years later, Brattain & Bardeen built the first working transistor, the germanium point-contact transistor, which was designed as the junction (sandwich) transistor.He tried to build one, but it didn't work.He reasoned that a strong electrical field could cause the flow of electricity within a nearby semiconductor.In 1945, Shockley had an idea for making a solid state device out of semiconductors.Field-effect transistors (FETs) Prepared by Engr Sarfaraz Khan Turk Lecturer at I BT LUMHS Jamshoro

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