SEMITIP V6, UniInt2, Example 2: n-type GaAs(110), with positive contact potential

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In most experimental situations, the "dopant-induced" component of the current is not observed or barely observed. This is because either the contact potential between tip and sample has a suitably large magnitude (positive for n-type material or negative for p-type material), or there are some extrinsic surface state that charge up (producing upwards band bending for n-type material or downwards band bending for p-type material), or both. In this example, we consider a positive contact potential of +1.5 eV for n-type material. The onset of the conduction band shifts to the right along the voltage axis and the dopant-induced component is greatly reduced, appearing only as a shoulder between about -0.9 and -1.3 V. Output for the conductance goes to FORT.15, which when plotted appears as:

NOTE: The small oscillation or irregularity in the conductance near 1.8 V is due to limited convergence in the computation. Changing the number of parallel wavevectors, the number of energy steps, and the target expansion factor in the integral to compute the current all from 20 to 50 (lines 41-43 of FORT.9) yields a much smoother result around this voltage.