Click here for input/output files for Example 1
It should be noted that the main reason for computations in a fully 3D geometry is for including spatial inhomogeneities (without radial nor azimuthal symmetry) in the semiconductor or on its surface. In this regard, the program MultInt3 provides a more general means of specifying such inhomogeneities than UniInt3 (see example within MultInt3 of treating a pn-junction viewed in cross-section). Within UniInt3 one can, however, specify inhomogeneous sources of fixed charge, by making program changes to the RHOBULK or RHOSURF routines as described in the SEMITIP V6 Technical Manual. In most such cases however, e.g. for point charges, the potential varies too rapidly with distance away from the charge to permit the calculation of tunnel currents using the integration of the Schrödinger equation along the central axis. Thus, for many 3D problems of interest, some program other than UniInt3 may be most appropriate. Nevertheless, our example of undoped GaAs is performed here, including computation of the current by integration of the Schrödinger equation, so that comparison can be made to Example 1 of UniPlane3 where the computation of the current is done using a plane wave expansion.
We consider undoped GaAs, with no surface states, and using a tip radius of 1 nm. Output for the current goes to FORT.91, FORT.92, and FORT.14 for the valence band (VB), conduction band (CB), and their sum, respectively. When we plot the total current (sum of current from extended states plus localized states) we find: