A GaAs MESFET structure was built using Silvaco TCAD:

• Channel Donor Electrons: 2e17

• Channel thicknes s : 0.1 microns

• Bottom layer: p doped GaAs (5 micron thick, 1e15p doping)

• Gate length: 0.3 micron

• Gate metal work function: 4.77eV

•Separation between the source and drain electrode: 1 micron

The IV curve is as follows. Of primary importance are the two bottom curves, which are for a gate voltage of -0.2V and -0.5V. The top curve is 0V, over which would be undesirable for the MESFET operation.

Now, in terms of designing a MESFET, there is a large amount of theory that one may need to grasp to build one from scratch – you would probably first start by building one similar to a more common iteration. That said, there are a number of parameters that one may wish to tweak and to achieve, to name a few: saturation current, threshold voltage, transit frequency, maximum frequency, pinch-off voltage.

The iteration above does not show a highly doped region under the source and drain contacts. The separation between source and drain may also be increased and the size of the gate decreased.

Channel doping level was found to make a significant difference in overall function. The channel must be doped to a certain level, otherwise the structure may not behave properly as a transistor.

go atlas

Title GaAs MESFET

# Define the mesh

mesh auto

x.m loc = 0 Spac=0.1

x.m loc = 1 Spac=0.05

x.m loc = 3 Spac=0.05

x.m loc = 4 Spac =0.1

# n region

region num=1 bottom thick = 0.1 material = GaAs NY = 10 donor = 2e17

# p region

region num=2 bottom thick = 5 material = GaAs NY = 4 acceptor = 1e15

# Electrode specification

elec num=1 name=source x.min=0.0 x.max=1.0 top

elec num=2 name=gate x.min=1.95 x.max=2.05 top

elec num=3 name=drain x.min=3.0 x.max=4 top

doping uniform conc=5.e18 n.type x.left=0. x.right=1 y.min=0 y.max=0.05

doping uniform conc=5.e18 n.type x.left=3 x.right=4 y.min=0 y.max=0.05

#Gate Metal Work Function

models fldmob srh optr fermidirac conmob print EVSATMOD=1

contact num=2 work=4.77

# specify lifetimes in GaAs and models

material material=GaAS taun0=1.e-8 taup0=1.e-8

method newton

solve vdrain=0.5

LOG outf=proj2mesfet500mVm.log

solve vgate=-2 vstep=0.25 vfinal=0 name=gate

save outf=proj2mesft.str

#Plotting

output band.param photogen opt.intens con.band val.band

tonyplot proj2mesft.str

tonyplot proj2mesfet500mVm.log

quit