MOSFET Device Physics and Operation

1 MOSFET Device Physicsand INTRODUCTIONA field effect transistor (FET) operates as a conducting semiconductor channel with twoohmic contacts thesourceand thedrain where the number of charge carriers in thechannel is controlled by a third contact thegate. In the vertical direction, the gate-channel-substrate structure (gate junction)can be regarded as an orthogonal two-terminaldevice, which is either a MOS structure or a reverse-biased rectifying Device that controlsthe mobile charge in the channel by capacitive coupling (field effect). Examples of FETsbased on these principles are metal-oxide-semiconductor FET ( MOSFET ), junction FET(JFET), metal-semiconductor FET (MESFET), and heterostructure FET (HFETs). In allcases, the stationary gate-channel impedanceis very large at normal operating basic FET structure is shown schematically in Figure most important FET is the MOSFET . In a silicon MOSFET , the gate contactis separated from the channel by an insulating silicon dioxide (SiO2) layer.

6 MOSFET DEVICE PHYSICS AND OPERATION Using Gauss’ law, we can relate the total charge Q s per unit area (carrier charge and depletion charge) in the semiconductor to the surface electric field by Q s =−ε sF s.(1.12) At the flat-band condition (V = VFB), the surface charge is equal to zero.In accumulation

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  Depletion, Mosfets

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