SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

424 CHAPTER 8. FIELD EFFECT TRANSISTORS

AlInAs

p – GaInAs substrate

GaInAs undoped buffer

Figure 8.47: Figure for problem 8.7.

v

ε

εs= 5 kv/cm

= 10,000 cm^2 /Vs

V = 2 x 10^7 cm/s

μ

Figure 8.48: Figure for problem 8.7.

Calculate the minimum width of the undepleted channel (near the drain side) withVGS=

0.5 V when (a)VDS=0.0V;(b)VDS=1.0V;(c)VDS=2.0V;(d)VDS=10V.

Problem 8.9(a) Ann-type GaAs MESFET is to be designed so that the device is just

turned off at a gate voltage ofVGS= 0 V. The Schottky barrier heightφbis 0.8 V and the

channel thickness is 0.2μm. Calculate the channel doping required. To calculate the

depletion region thickness (only) you may assume thatVbi∼=φb-0.1V.

(b) If a gate bias of 0.2 V is applied, calculate thegatecurrent.

(c) What is the saturation drain current when the gate bias is 0.2 V? Compare the gate

current with the drain current.

Mobility,μn = 5000 cm^2 /V·s

Gate length,L=2. 0 μm

Gate width,Z=20. 0 μm

Channel width,h=0. 2 μm