Geometric and local electronic structure of Si(111)-As.

The Si(111)-As surface is imaged by scanning tunneling under UHV conditions. A three-fold symmetric 1x1 structure is observed, consistent with models suggesting substitution of As for Si in the outer half of the top double-layer. No evidence for residual stacking faults on the scale of the 7x7 mesh is detected. I-V characteristics of the junction show an energy gap of 1. 9 to 2.2eV consistent with an empty surface state in the projected gap and a filled state resonant with the bulk as predicted by self-energy calculations for this surface.