The junction field-effect transistor (JFET) or junction-gate FET was originally proposed by Shockley in 1952. The first JFET was realized by Dacey and Ross in 1953. During the 1950s, major activities were concentrated on the bipolar transistor invented in 1948. The 1960s, on the other hand, saw rapid development of the MOSFET, which was started in 1960. The advancement of JFET technology was made mainly in the 1970s, especially when the enhancement-mode device was made practical around 1977. The JFET is similar to IGFET and MOSFET, and it serves as an alternative to these devices.
For n-channel devices, the dopant types are simply the opposite. In Si JFETs, the heavily doped substrate usually serves as the bottom gate. The active layer of n-region can be grown epitaxially or formed by ion implantation or diffusion. For GaAs devices, an intrinsic semi-insulating substrate is usually used, and a bottom gate is absent. In all cases, the top gate defines the channel length L. The distance between the top gate and the source or drain should be kept small to minimize the series resistance of the device.
The operation of a JFET is based on the modulation of the junction depletion width by the gate bias to control the net channel opening. The gate bias is applied to both the top and the bottom gates. For operation with a single gate, the analysis has to be modified slightly.