  By means of scanning tunneling spectroscopy (STS) we study the electronic
structure of the III-V semiconductor surface InAs(111)A in the field emission
regime (above the vacuum level). At high sample bias voltages (approaching +10
V), a series of well defined resonances are identified as the typical Stark
shifted image states that are commonly found on metallic surfaces in the form
of field emission resonances (FER). At lower bias voltages, a more complex
situation arises. Up to three double peaks are identified as the first three
FERs that are split due to their interaction with the periodic surface
potential. The high corrugation of this potential is also quantified by means
of density functional theory (DFT) calculations. Another sharp resonance not
belonging to the FER series is associated with an unoccupied surface state.
