Asymmetry of acceptor wave functions caused by surface-related strain and electric field in InAs

The spatial distribution of the local density of states at Mn acceptors near the (110) surface of p-doped InAs is investigated by scanning tunneling microscopy. The shapes of the acceptor contrasts for different dopant depths under the surface are analyzed. Acceptors located within the first ten subsurface layers of the semiconductor show a lower symmetry than expected from theoretical predictions for the bulk acceptor wave function. They exhibit a (001) mirror asymmetry. The degree of asymmetry depends on the acceptor atoms' depths. The measured contrasts for acceptors buried below the tenth subsurface layer closely match the theoretically derived shape. Two effects are able to cause the observed symmetry reduction, i.e., the strain field of the surface relaxation and the tip-induced electric field. While both effects induce similar asymmetries, a comparison of their relative strengths indicates that surface-related strain is the dominant effect for Mn in InAs.