Depletion mode versus enhancement mode

The JFET works by varying width of channel. Generally the channel is wide open; as the depletion region becomes wider and wider, choking off channel, charge carriers are forced to pass through the narrower and narrower path. This is called as the depletion  mode of operation for the field-effect transistor.

A MOSFET can also be made to work in depletion mode. The drawings and schematic symbols show depletion-mode MOSFETs.However, MOS technology allows an entirely different means of operation. The enhancement mode MOSFET has a pinched-off channel. It is required to apply a bias voltage, EG, to gate so that a channel will form. If EG = 0 in such a MOSFET, that is, if device is at zero bias, drain current ID is zero when there is no signal input.

The schematic symbols for N-channel and P-channel enhancement mode devices are shown in the Figure given below. The vertical line is broken. By this you can recognize an enhancement mode device in the circuit diagrams

                         Figure- Schematic symbols for enhancement mode MOSFETs. At point A, N-channel; at point B, P-channel