Hello all,

I have been trying to obtain the breakdown characteristics of a very simple GaN HEMT device. The device, however, does not enter breakdown even for very high voltages as can be seen in the tonyplot image attached.

I faced the same issue in my previous HEMT structure which was quite complicated in design. Hence, I have created this smaller, simple design which will be easier to spot mistakes in.

I have used the field mobility model, the srh model, fermi model, pch.elec model and most importantly for breakdown, the selb impact ionisation model.

Apart from simple ramp voltage variation, I have also used current boundary conditions, compliance parameters as well as traceback- but to no avail.

If anybody could help me with what declarations to include, models to specify, or even modify my code, I would be immensely thankful.

Code:

#basic HEMT structure and analysing breakdown

go atlas

#meshing defintion

mesh width=50

x.mesh l=0 s=0.05

x.mesh l=1 s=0.05

y.mesh l=-0.05 s=0.05

y.mesh l=0.09 s=0.05

y.mesh l=0.1 s=0.01

y.mesh l=0.15 s=0.01

y.mesh l=0.20 s=0.05

y.mesh l=0.30 s=0.05

#region defintion

region num=1 mat=air y.min=-0.05 y.max=0.3

region num=2 mat=AlGan y.min=0 y.max=0.1 donors=3e17

region num=3 mat=GaN y.min=0.1 y.max=0.3 donors=1e15

#electrode definition

elec num=1 name=source y.min=-0.05 y.max=0.15 x.min=0 x.max=0.05

elec num=2 name=drain y.min=-0.05 y.max=0.15 x.min=0.95 x.max=1

elec num=3 name=gate y.min=-0.05 y.max=0 x.min=0.45 x.max=0.55

#doping definition

doping gaussian characterisitic=0.01 conc=1e19 n.type x.left=0 x.right=0.09 \

y.top=0.1 y.bottom=0.19 ratio.lateral=0.01 direction=y

doping gaussian characterisitic=0.01 conc=1e19 n.type x.left=0.91 x.right=1 \

y.top=0.1 y.bottom=0.19 ratio.lateral=0.01 direction=y

doping gaussian characterisitic=0.01 conc=3e17 n.type x.left=0 x.right=1 \

y.top=0 y.bottom=0.1 ratio.lateral=0.01 direction=y

doping gaussian characterisitic=0.01 conc=1e15 n.type x.left=0 x.right=1 \

y.top=0.1 y.bottom=0.3 ratio.lateral=0.01 direction=y

#displaying the structure

save outf=basicStructure.str

tonyplot basicStructure.str

#models definition

model print fermi fldmob srh pch.elec

impact selb

#contact definition

contact name=gate workfunction=4.8

#method specification

method newton itlim=35 trap maxtrap=10 carriers=1

output con.band val.band band.param charge e.mob h.mob flowlines qss

#idvd analysis

solve init

log outf=basicHEMT.log

solve vstep=0.1 vfinal=1 name=drain

solve vstep=1 vfinal=10 name=drain

solve vstep=2 vfinal=20 name=drain

solve vstep=5 vfinal=1200 name=drain cname=drain compl=1.0

save outf=basicStructure.str

tonyplot basicHEMT.log

quit