SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

8.6. POLAR MATERIALS AND STRUCTURES 393

eφs

ΔEc

V- EF

edi

eVdi+

Z

ns

eNDD+

(a)

(b)

(c)

{ {

AlGaN GaN

2DEG

• dAlGaN 0 Δd

dAlGaN

D

Substrate

-Qπ(AlGaN)

+Qπ(AlGaN)

-Qπ(GaN)

+Qπ(GaN)

-Qscr

EC

Figure 8.22: Polar heterostructures can generate a 2DEG which is used as the channel region of
an HFET. (a) Typical AlGaN/GaN heterostructure used in polar HFET technology, along with
(b) the charge distribution and (c) the band diagram of the structure.