SEMITIP V6, Mult1, Example 1: GaAs(110) with 10 nm thick undoped region on n-type material

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

This example illustrates a simple band bending computation for GaAs that has a 10 nm thick undoped layer on top of 1018 cm-3 doped n-type material, assuming a contact potential of 0 eV and a sample-tip voltage of 1 V. The semiconductor is thus in depletion. Intrinisic surface states are present just above the conduction band edge (lines 34-37 of the FORT.9 input file), but they play no role in the solution. Output to FORT.11 gives the electrostatic potential energy (column 2) vs. the z-distance through the vacuum and semiconductor (column 1). When plotted, the potential appear as:

In this example, region 1 of the semiconductor (lines 5-17 of FORT.9) is defined as the undoped semiconductor, and region 2 (lines 18-30 for FORT.9) is defined as the n-type semiconductor. The zero of the electrostatic potential energy corresponds to the situation when region 1 is charge neutral (i.e. Fermi level at midgap in region 1). But, since region 2 lies below region 1, and deep inside region 2 (when it is charge neutral) the electrostatic potential energy is about 0.7 eV (half a band gap) different than for region 1, then the electrostatic potential does not approach zero deep in region 2 but rather it approaches a value of about -0.7 eV. This example can be compared with Example 1 of Uni1, which does not have the undoped layer on the top of the semiconductor. There is more band bending in the present case, as expected because of the presence of the undoped layer.