SEMITIP V6, program Uni3
Introduction
This program computes the electrostatic potential between a metallic tip and a uniform (homogeneous) semiconducting sample, for a 3dimensional geometry.
Version information
Version 6.3; see top of
Uni36.3.f
source code for prior version information.
Usage
A compiled version of the code, which should run on any Windows PC, is
available in the file Uni3.exe.
Input for the executable code comes from the file FORT.9.
Download these two files, into filenames "Uni3.exe" and "fort.9". Then, run the code just by double clicking on it. Using a text editor, the input parameters in FORT.9 can be changed to whatever values are desired. In addition to the parameter values, this file also contains comments as to the meaning of each parameter. See
SEMITIP V6 Technical Manual
for additional comments on the meaning of the parameters.
Output
Output from the program is contained in the following files
(output depends on the value of the output parameter IWRIT as specified
in the input file FORT.9):
 FORT.10  gives the numerical results for the following quantities:
 tip radius of curvature (nm)
 tipsample separation (nm)
 sampletip bias voltage (V)
 contact potential (eV)
 Pot0  the surface potential at the semiconductor surface (eV).
 FORT.11  provides the potential (eV) along the central axis, as a
function of zdistance (output for IWRIT>=1)
 FORT.12  provides the potential (eV) along the surface, for specified angle from xaxis, as a function
of the radial distance from the central axis (output for IWRIT>=1)
 FORT.13  gives the entire array of potential values (eV) (output for IWRIT>=3); see
SEMITIP V6 documentation
for more details.
 FORT.16  gives an exact copy of the output to the console
 FORT.20, FORT.21, ...  contour lines (nm) of the potential, for specified angle from xaxis (output for IWRIT>=2)
 FORT.81, FORT.82,...  listing of surface charge density (column 2) vs. Fermi energy (column 1), for various areas (output for IWRITE>=3)
All of the parameters in the program can be varied using the input file FORT.9, with the exception of the array sizes, the specification of a surface state density other than a uniform or Gaussian shaped one, and the specification of spatial arrangement of bulk or surface charge density. See
SEMITIP V6 Technical Manual
for additional information on these userdefined functions. Modification of those functions
can be accomplished by changing the source code of the program. The source code is available, in the following files (version numbers follow the dash in the names):

Uni36.3.f 
main program.

contr36.0.f 
routine for outputting contour plot.

gsect6.0.f 
general purpose Golden Section search routine, for dealing with nonlinear aspects of the problem.

semirho6.0.f 
routines for computing semiconductor charge densities.

semitip36.1.f 
performs the detailed finite element solution of Poisson's equation.

surfrho6.2.f 
routines for handling surface charge densities.
All routines are written in Fortran. The source code can be downloaded
directly from the above locations, and it can be compiled and linked
on any platform. Sample input and output from the program is shown in the examples below.
Illustrative Examples of Running the Code

ntype GaAs(110)

ntype GaAs(110), with offcenter fixed charge.