SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

460 CHAPTER 9. FIELD EFFECT TRANSISTORS: MOSFET

Ιnversion Condition When

Ec VSB = 0

EFi

EF

Ev

eVs = –2eφF

(b)

Ιnversion Condition When

VSB > 0

EFi

EF

eVs = e(–2φF + VSB)

(c)

EFn

Electron Quasi

Fermi Level

W(VSB)

p-substrate

S G D

(a)

n+ n+

VD

VSB

n-MOSFET with

VSBBias

VG

Wmax

Ec

Ev

Figure 9.17: (a) Ann-MOSFET showing the voltage between the source and the body of the
transistor; (b) band profiles of the MOSFET withVSB= 0 at the inversion condition; (c) band
profile of the MOSFET whenVSB> 0. The depletion width increases whenVSB> 0.