
		A SHORT BASE PN DIODE EXAMPLE


In this diode example, the user will introduced to a variety of simulations
which include forward current versus voltage characteristics, transient
response, ramped diode simulation and AC analysis.

To start things off, file pn1a.p2 describes the pn diode device.  This device
is 5um x 1um, and as such constitutes a short base diode.  The mesh is 
generated and stored in a file called pn.msh.  The n-type side of the 
device is doped with the concentration of 1e15, while the p-type is doped
to a concentration of 1e19.  This file also plots the grid and the doping.

A file called pn2a.p2 solves for the forward bias IV characteristics.  This 
file reads in the mesh, then defines a contact resistance so that a hard
voltage is not impressed across the pn junction.  A two carrier newton
solution is used for this simulation.  Initial solution at zero bias is 
solved and saved in a file called pn2a0-r.slv.  A log file called 
IV-r.log is started to save the simulation data.  The n side of the junction
is grounded and the p side is stepped up in voltage from 0 to 2 volts.
The solution at 2 volts is saved in a file called pn2a2-r.slv.

To see the difference between in the IV characteristics with and without the
contact resistance, a file called pn2aa.p2 does exactly what pn2a.p2 did 
except without the contact resistance.  The log file in this case is called
IV-nr.log, where the nr stands for no resistance.  Similarly, the initial 
solution is stored in pn2a0-nr.slv, and the solution at 2 volts is saved
is pn2a2-nr.slv.

File pn3a.p2 plots the results of the previous simulations, and shows the
comparison between the simulation with and without the contact resistance.
This file also plot the diode voltage V1 versus VA1, the applied voltage.

The transient simulation for the diode is done by a file called pn4.p2.
The step voltage is applied to the diode such that the diode goes from 
positive 2 volts to negative 2 volts.  The solution from past simulation
at 2 volts is loaded in by the file called pn2a2-r.slv.  A log file called
IV-step.log is started to keep track of the transient response of the
diode to the step input.  The output characteristics for the step input
are then plotted.  The simulation shows that the diode saturation time
is 1ns, this is the time required to extract the stored charge from the
forward biased state so that the diode becomes reverse biased.  A plot
is also included of the automatic time-step estimator so that its 
efficiency can be evaluated.

A ramped diode response is also simulated.  This is done by a file called
pn8.p2.  Here the voltage is again changed from +2 volts to -2 volts except
this time its ramped instead of a step.  This is indicated by the endramp
in the solve statement.  The ramp last for 2.5ns.  The saturation voltage 
due to this change now doubles as is obivious from the simulation plots.

Finally, small signal AC analysis simulations are conducted on the diode.
The two carrier newton method is used for this simulation.  The zero bias
solution is loaded.  A log file is started save the AC simulation data.  
The AC analysis is done at 1 KHz.  The capacitance of the device is  
plotted against the voltage.  The diode voltage is varied from -3 volts to
+0.5 volts.  The logarithim of the conductivity is also plotted over the
same voltage range.  
