430 CHAPTER 8. FIELD EFFECT TRANSISTORS
AlInAs
GaInAs
p+GaInAs (for part 2 of the problem )
250 nm
5 nm
1 μm
Si sheet
Surface (φB= 1eV)
Figure 8.51: Figure for problem 8.28.
parameters:
Schottky barrier height, φb =0.8V
Gate length, L =3. 0 μm
Channel mobility, μn = 6000 cm^2 /V·s
Channel doping, Nd =5× 1016 cm−^3
Channel depth, h =0. 5 μm
Gate width, Z =25μm
Calculate the intrinsic transconductance of the device. If the source-to-gate separation is
0.5μm, calculate the value of the extrinsic transconductance.
Problem 8.30Calculate the maximum cutoff frequency for the ideal device of problem
8.24 (with the source resistance assumed equal to zero). Calculate the degradation in the
cutoff frequency due to the effect of the source series resistance.
Problem 8.31Consider ann-type GaAs MESFET at 300 K with the following
parameters:
Schottky barrier height, φb =0.8V
Channel doping, Nd =10^17 cm−^3
Channel mobility, μn = 6000 cm^2 /V·s
Channel depth, h =0. 2 μm
Channel width, Z =2. 0 μm
Channel length, L =1. 0 μm
Calculate the maximum cutoff frequency using the constant-mobility model and the
saturation velocity model.
Problem 8.32An important effect in short-channel FETs made from high-mobility
materials like GaAs and InGaAs is the “velocity overshoot effect.” The average time for
