SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

376 CHAPTER 8. FIELD EFFECT TRANSISTORS

Source

Gate

Drain

Undoped GaAs

2DEG

n+ GaAs

n+ Al GaAs

A GaAsl

Undoped

Semi-insulating GaAs Substrate

(a)

Ionized Donors

2DEG

E 1

EF

Gate

Metal

n+AlGaAs

Donor Layer

AlGaAs

Spacer

GaAs

Buffer

S.I.

Substrate

Triangular

Quantum Well

(b)

E 2

Figure 8.13: (a) A schematic of a GaAs/AlGaAs MODFET. In the figure shown, the gate is
“recessed” to have a better control over the 2-dimensional electron gas (2DEG). (b) The band
profile of ann-MODFET showing bandbending leading to a triangular quantum well at the
GaAs/AlGaAs interface.