Comparison betweenab initiotheory and scanning tunneling microscopy for (110) surfaces of III-V semiconductors

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Abstract
We compare results of ab initio electronic structure calculations using density-functional theory with measured scanning tunneling microscopy (STM) images for the clean (110) surface of III-V semiconductors. A detailed analysis is made of the nature of the wave functions contributing to STM images. The atomic structure has been determined by total-energy minimization combined with the plane-wave pseudopotential technique. The nature of the wave functions (surface localization, surface resonance, or bulklike) has been determined for energies in the range of 3 eV on both sides of the fundamental gap. In particular, the decay of the density profiles into the vacuum as well as into the bulk has been analyzed. A consistent understanding of the voltage-dependent STM images has been obtained. For tunneling out of the occupied states the dangling bond at the anion gives the main contribution for all voltages measured. On the other hand, for tunneling into the empty states the dangling bond at the cation is important only for small voltages. For higher voltages resonances (backbond but also some bridgebond contributions) dominate the STM image, yielding the observed rotation of the apparent row direction.