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6. Press the Load Example button. The input command file for the example will be copied into your current working directory together with any associated files. A copy of the command file will be loaded into DECKBUILD. Note that the Load Example button remains faded out until this step is performed correctly.
7. Press the Run button in the middle frame of the DECKBUILD application window to run the example. Alternatively, most examples are supplied with results that are copied into the current working directory along with the input file. To view the results, select (highlight) the name of the results file and select Tools-Plot. Details on using TONYPLOT can be found in the VWF INTERACTIVE TOOLS USER’S MANUALS.
go atlas
TITLE PN Diode Breakdown Simulation with curve tracing algorithm
# SILVACO International 1996
mesh
x.m l=0.0 spac=1.0#structure
x.m l=1.0 spac=1.0#structure
y.m l=0 spac=1.0#structure
y.m l=5.0 spac=0.005#structure
y.m l=15 spac=2#structure
region num=1 silicon#material
electrode top name=emitter#structure
electrode bottom name=base#structure
doping uniform conc=5e17 p.type #doping
doping uniform n.type conc=1.e20 x.l=0. x.r=1 y.t=0.0 y.b=5.0# doping
save outf=diodeex03_0.str # solution specification
#tonyplot diodeex03_0.str -set diodeex03_0.set# result analysis
models srh conmob bgn auger fldmob # models
impact crowell # models
solve init # solution specification
solve # solution specification
solve vemitter=0.1 # solution specification
method newton climit=1.e-4 #numerical method selection
curvetrace end.val=1e-4 contr.name=emitter curr.cont mincur=1e-13 nextst.ratio=1.2
# result analysis
log outf=diodeex03.log # result analysis
solve curvetrace # result analysis
tonyplot diodeex03.log -set diodeex03.set # result analysis
quit
The first part of the program (Deckbuild up) gives the 2-D mesh description of the cross-sectional view of the emitter-base diode. The upper part of the cross-sectional view is Emitter (N type) which has an uniform doping of 10 20 Phosphorous atoms per c.c. and lower part is Base (P-type) which has an uniform doping of 5×10 17 Boron atoms per c.c. as shown in Figure 7.3.
It uses the models given in Table 7.2.
In Method statement we give the Numerical Method adopted for carrying the calculations.
In weakly coupled systems we use Gummel Numerical Method where we regard the system as decoupled and we analyze the nodes one by one. This has linear convergence.
In strongly coupled systems we use Newton Numerical Method . This has quadratic convergence.
In Block system we start as decoupled system and then we use coupling.
In the example above we have used Newton Method.
We have carried out two simulations.
Table 7.2. The Models used in this program
| Model | Syntex | Notes |
| Shockley-Hall-Reed indirect recombination | SRH | This describes the method of indirect recombination mediated by traps and defects. |
| Concentration Dependent Mobility | CONMOB | Impurity scattering is considered along with lattice scattering. |
| Band Gap Narrowing | bgn | Emitter has heavy doping leading to band gap narrowing this adversely effects the emitter injection efficiency.(This has been elaborately explained in Appendix IV of IC journey from Micro to Nano Era. This Appendix is a part of SSPD collection) |
| Auger Direct Recombination | auger | Whenever carrier concentrations are high they directly recombine. In that case trap mediation is not required. |
| Field Dependent Mobility | fldmob | At high fields where drift velocity is comparable to the thermal velocity the drift velocity saturates to scatter limited velocity. |
| Crowell-Sze model | impact crowell | Impact ionization model has to be used while modelling the Avalanche Breakdown |
Figure 7.3. 2D Mesh describing the cross-sectional area of the Device.
It should be noted that lightly doped portion base is being covered by fine mesh whereas heavily doped emitter is covered by coarse mesh. In One-sided step Junction (N+P) minority carriers electron in P-side carry the major part of the diode current hence minority carrier distribution in P-side have to be more accurately analyzed hence base is being covered by a finer mesh.
Figure 3. Simulation Number 1 tony plot. BVz = 5V
go atlas
TITLE PN Diode Breakdown Simulation with curve tracing algorithm
# SILVACO International 1996
mesh
x.m l=0.0 spac=1.0
x.m l=1.0 spac=1.0
y.m l=0 spac=1.0
y.m l=5.0 spac=0.005
y.m l=15 spac=2
region num=1 silicon
electrode top name=emitter
electrode bottom name=base
doping uniform conc=5e16 p.type
doping uniform n.type conc=1.e20 x.l=0. x.r=1 y.t=0.0 y.b=5.0
save outf=diodeex03_0.str
#tonyplot diodeex03_0.str -set diodeex03_0.set
models srh conmob bgn auger fldmob
impact crowell
solve init
solve
solve vemitter=0.1
method newton climit=1.e-4
curvetrace end.val=1e-4 contr.name=emitter curr.cont mincur=1e-13 nextst.ratio=1.2
log outf=diodeex03.log
solve curvetrace
tonyplot diodeex03.log -set diodeex03.set
quit
Figure 4. Simulation Number 2 tony plot. BVa = 20V.
7.3.1.4. Discussion of the two simulations carried out in the previous section.
We have just carried out two device simulations for PN Junction breakdown with curve tracing algorithm.
In first device, base had a concentration of 5×10 17 Boron atoms per cc. This corresponded to a reverse Avalanche Breakdown of 5V. At an emitter doping of 1×10 20 /cc we should have invoked ‘Tunnelling Model’ and obtained Zener Break down.
In second device base had a concentration of 5×10 16 Boron atoms per cc. This corresponded to a reverse Avalanche Breakdown of 20V.
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