SEMITIP V6, MultInt3, Example 1: GaAs(110) pn junction

Click here for input/output files and main program source code for Example 1

This example illustrates the conductance vs. voltage for a pn junction in GaAs, as viewed in cross-section with the junction directly below the probe tip. Region 1 is defined as the n-type region, extending over x<=0, and region 2 is the p-type region extending over x>0. The spatial extent of the regions are defined in the routine IGETREG, located in the same file as the MultInt3.f main program: 

      INTEGER FUNCTION IGETREG(X,Y,S)
      COMMON/TIPPOS/X0,Y0
C
      IGETREG=1
      IF ((X+X0).GT.0.) IGETREG=2
      RETURN
      END
with the parameters defining the regions given in the FORT.9 input file. This problem has a mirror plane lying along the x-axis, so line 48 in the FORT.9 file is set to 1 thus including that mirror plane in the computation (hence permitting fewer angular grid points thereby reducing the computation time). Band bending for this geometry is shown in example 1 of Mult3.f.

The conductance vs. voltage, from FORT.15, appears as:

We see a Fermi level (0 V in the plot) located near the midgap position in the spectrum, as expected. (Far from the junction the conductance vs. voltage will appear more similar to that for n-type or p-type material. Thoses cases can be computed simply by changing the tip x-position, line 7 for FORT.9). For example, with a tip x-position of -5 nm (in the n-type material) we obtain
and with an x-position of +5 nm (in the p-type material) we obtain