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 near a semiconducting surface by solving the Poisson- and continuity equations for holes and electrons in a semiconductor. P_SpaceChargeLight takes into account non-equilibrium charge carriers, generated, e.g., by band-to-band transitions when the semiconductor is excited by laser light.
The Poisson- and continuity equations are solved numerically in three dimensions with the help of a finite-difference algorithm. The tunnel current components are calculated in Bardeen’s approximation , which has been further developed and adapted by Harrison , Bono and Good  and Feenstra . For this purpose, the potential and charge carrier concentrations along the central axis through the tip apex are used. Non-equilibrium charge carriers are taken into account in the tunnel current calculation by introducing quasi-Fermini levels. P_SpaceChargeLight is written in the Pascal language and can be compiled for nearly any operating system.
The source code is available from GitHub
 J. Bardeen: Tunnelling from a many-particle point of view, Phys. Rev. Lett. 6 (1961) 57-59.
 W. A. Harrison: Tunneling from an independent-particle point of view, Phys. Rev. 123 (1961) 85-89.
 J. Bono, R. H. Good Jr.: Theoretical discussion of the scanning tunneling microscope applied to a semiconductor surface, Surf. Sci. 175 (1986) 415-420.
 R. M. Feenstra, and J. A. Stroscio: Tunneling spectroscopy of the GaAs(110) surface, J. Vac. Sci. Technol. B 5 (1987) 923-929.