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P_SpaceChargeLight is a tunnel current simulation software package developed by Michael Schnedler. It takes into account the influence of the electric field of a metallic probe tip in proximity to a semiconducting surface by solving the Poisson and continuity equations for holes and electrons in a semiconductor in three dimensions, prior to the derivation of the tunnel current.

P_SpaceChargeLight is capable of simulating the redistribution of non-equilibrium charge carriers that are created e.g. by band-to-band transitions due to laser irradiation.

Simulation software packageTip-induced band bending caused by the electrostatic potential of a STM-tip. Simulation was performed using the P_SpaceChargeLight software package.
Copyright: FZ Jülich, ER-C

The numerical Poisson and continuity equation solver is based on a finite-difference scheme. Tunnel currents are computed in Bardeen’s approximation [1], which was further developed and adapted by Harrison [2], Bono and Good [3] and Feenstra [4].

The potential and carrier concentrations along the central axis through the tip apex are used to derive the tunnel current in a one-dimensional approximation. Excess carriers are included in the tunnel current computation by introducing quasi Fermi levels.

P_SpaceChargeLight is written in Pascal and can be compiled for any operating system, since it does not make use of WinAPI.

[1] J. Bardeen: Tunnelling from a many-particle point of view, Phys. Rev. Lett. 6 (1961) 57-59.
[2] W. A. Harrison: Tunneling from an independent-particle point of view, Phys. Rev. 123 (1961) 85-89.
[3] J. Bono, R. H. Good Jr.: Theoretical discussion of the scanning tunneling microscope applied to a semiconductor surface, Surf. Sci. 175 (1986) 415-420.
[4] R. M. Feenstra, and J. A. Stroscio: Tunneling spectroscopy of the GaAs(110) surface, J. Vac. Sci. Technol. B 5 (1987) 923-929.