SEMITIP V6, program Mult3

Introduction

Version information

Usage

• The routine IGETREG (at the bottom of the source code) defines the various regions in the semiconductor. The input parameters x, y, and S are the X, Y, and z positions in the semiconductor, respectively. The routine should return an integer value giving the number of the region for those specified positions (i.e. return a value of 1 to use the first set of parameters in the FORT.9 input file defining the semiconductor region, a value of 2 for the second set of parameters, etc.).
• The maximum number of region types in the semiconductor is specified by the parameter NREGDIM and the maximum number of area types on the surface by the parameter NARDIM. The values of these parameters are set in the main programs and its associated routines by PARAMETER statements. By default these values are set to 2, but they can be increased by changing all of the PARAMETER statements.

Output

• FORT.10 - gives the numerical results for the following quantities:
  • tip radius of curvature (nm)
  • tip-sample separation (nm)
  • sample-tip bias voltage (V)
  • contact potential (eV)
  • Pot0 - the surface potential at the semiconductor surface (eV).
• FORT.11 - provides the electrostatic potential energy (eV) along the z axis, as a function of distance (output for IWRIT>=1). Also, the electrostatic potential plus the vacuum barrier energy is output to FORT.95, and the energy of the valence and conduction band edges (as used in computing the tunnel current) are output to FORT.96 and FORT.97, respectively.
• FORT.12 - provides the potential (eV) along the surface, for specified angle from x-axis, 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 VERSION 6 Technical Manual 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 x-axis (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 user-defined 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):

• Mult3-6.3.f - main program, available in example(s) below.
• contr3-6.0.f - routine for outputting contour plot.
• gsect-6.0.f - general purpose Golden Section search routine, for dealing with nonlinear aspects of the problem.
• semirhomult-6.0.f - routines for computing semiconductor charge densities.
• semitip3-6.1.f - performs the detailed finite element solution of Poisson's equation.
• surfrhomult-6.2.f - routines for handling surface charge densities.

Illustrative Examples of Running the Code

1. GaAs(110) pn junction
2. GaAs(110) with probe tip located between two surface steps
3. Si(111)2x1, with different areas of 2x1 reconstruction