SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

438 CHAPTER 9. FIELD EFFECT TRANSISTORS: MOSFET

(a)

(b)

(c)

dox

M

O

S

fs

fM

fM

fs

FB

Metal

Metal

Oxide

(Oxide)

Oxide (insulator)

Semiconductor

EC

EC

EC

EC

EV

EV

EV

EV

EF

EF

EF

Evac

Evac

Evac E

vac

Vbi=−(φm−φs)=φms

Vfb=Vbi=−φms

eVfb

eχS

eφs

eφs

eφs

eφm

eφm

eφm

p−type semiconductor

Figure 9.6: (a) A schematic of an MOS capacitor. (b) Band profiles of the isolated metal, oxide,
and semiconductor. Shown are the metal work function, semiconductor work function, and
electron affinity. (c) Band profile of the MOS structure in equilibrium and in flatband.