fet is fiels effect transistor .jfet and mosfet are under the category of fet.JFET is junction field effect transistor and mosfet is metal oxide semiconductor field effect transistor.
as the name indicates,it is device which is used in electric devices as fast on -off switch.when diode is in forward bias condition then the diode is in on state i.e.the electric ckt is on and if diode id in reverese bias state then diode is in off state i.e. electric ckt is in off state.thus...
diode without any battery has no mean.any diode inividually is of no use. actually when u will short a diode then a depletion layer forms which prevent the flow of free charge carriers.so there will be no curent in diode.