SEMITIP, VERSION 3, Electrostatic Computations for a Probe Tip near a Semiconductor

R. M. Feenstra
Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213

This program computes the electrostatic potential resulting from a metallic probe tip near a semiconductor, as described here. This program is an updated version of the prior VERSION 2, described here, and VERSION 1, described here. A preprint of a paper describing the modifications made to the theory for VERSION 3 is available here, and this paper appeared in J. Appl. Phys. 103, 073704 (2008).

A compiled version of the code, which should run on any Windows PC, is available in the file semitip_v3.exe. Input for the executable code comes from the file FORT.9. Download these two files, into filenames "semitip_v3.exe" and "fort.9". Depending on your browser this download can probably most easily be done by RIGHT CLICKING on the files when you see them listed (i.e. after clicking on the above links), and then clicking on SAVE TARGET AS and saving them into the directory of your choice using the ALL FILES filetype. 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.

Output from the program is contained in the following files (output depends on the value of the input parameter IWRIT as specified in the input file FORT.9):

• FORT.10 - gives the numerical results for the following quantities:
  • tip radius of curvature
  • tip-sample separation
  • tip potential
  • opening angle of tip shank
  • PHI0 - the surface potential at a point directly opposite the tip apex
• FORT.11 - provides the potential along the central axis, as a function of z-distance (output for IWRIT>0)
• FORT.12 - provides the potential along the surface, as a function of the radial distance from the central axis (output for IWRIT>0)
• FORT.13 - gives the entire array of potential values (output for IWRIT>2)
• FORT.16 - gives an exact copy of the output to the console
• FORT.20, FORT.21, ... - contour lines of the potential (output for IWRIT>1)

All of the parameters in the program can be varied using the input file FORT.9, with the exception of the array sizes (NR,NV,NS, and NE), the specification of an auxiliary function other than a hemisphere which defines a protrusion on the end of the probe tip, and the specification of a surface state density other than a uniform one. Modification of those parameters can be accomplished by changing the source code of the program. The source code is also available, in the files:

• SEMITIP_V3.F - main routine.
• SEMITIP2.F - performs the detailed finite element solution of Poisson's equation.
• SEMIRHO.F - auxiliary routines for computing semiconductor charge densities.
• SURFRHO.F - auxiliary routines for handling surface charge densities.
• CONTR.F - plots contour lines of the computed potential.