Page 991 - Basic Electrical Engineering

between the drain and the source. A MOSFET is commercially more
important than JFET because the MOS devices are suitable for very large-
scale integration. MOSFET can be n-channel-type or p-channel-type channel

formed between the source and the Drain. MOSFET, either n-channel or p-
channel type can further be categorized into enhancement MOSFET or

depletion MOSFET.

Figure 14.29 EMOSFET constructional details

14.9.1 The Enhancement MOSFET (EMOSFET)

The constructional details of an EMOSFET has been shown in Fig. 14.29. In
an n-channel EMOSFET two blocks of heavily doped n-type material have
been diffused into a p-type substrate or a base (a substrate is a surface or

material on which a device is made or developed/grown). The terminals for
external connection have been brought out. The whole of the surface has been

coated with a layer of silicon dioxide. A thin metal plate has been placed on
the surface of the silicon dioxide layer wherefrom the gate terminal
connection has been taken. In fact, the metal plate itself will function as the

gate of the MOSFET. The substrate is a high resistive material.
It may be noted that no continuous channel exists between the source and

the drain. The two n-blocks forming the drain and the source, makes two p–n
junctions with the p-type substrate. When a positive voltage, V is applied
DS