SEMITIP v6, UniPlane3, Example 4: InAs quantum dot in GaAs, showing dot outline

Click here for source and input/output files for Example 4

This example uses the same parameters for a probe tip located near an InAs quantum dot in GaAs as in example 2 and example 3, but now illustrates using an output parameter value of 7 and an IPOT value of 0 in the QDplanecurr3.f routine, to plot the outline of the quantum dot. A series of images are output, img1.PGM, img2.PGM, ..., img9.PGM, consisting of the outline of the dot (actually the conduction band edge of the dot) in the surface plane, one z increment below that, etc. For this situation of 6 k-values in each of the x, y, and z directions, the net number of grid points in the x, y, and z directions is 24, 12, and 12, respectively (for the y and z directions those 12 points are only half of the supercell, but the cell is periodic around its midplane in those directions so only the 12 points in the half-cell need be considered). By default in the QDplanecurr3.f routine these maps are expanded by a factor of 3, yielding 72 x 36 pixels in the x and y directions, respectively. Those image are output into the imgx.PGM files, by default, onto a standard image size of 512x512 pixels. Thus, cutting the 72x36 sections of those yields the outline of the dot in each of the surface planes. The images appear as:

In these images the quantum dot appears black, against a gray background. The tip position (using 0 nm offset between tip and dot in the FORT.9 input file) corresponds to the midpoint of the bottom edge of each image. As the depth into the semiconductor increases, the outline of the dot gets smaller, as expected. For the limited number of k-points used in this computation, the size of the region used in the plane wave expansion is actually somewhat too small to fully encompass the dot (hence it appears cut off in the y-direction).