Low-temperature scanning tunneling spectroscopy of n-type GaAs(110) surfaces

Scanning tunneling spectroscopy is used to study n-type GaAs(110) surfaces at temperatures near 10 K. Spectral lines associated with surface accumulation layer states are observed. Near dopant atoms, three additional lines are seen in the spectra. These lines are identified with the shallow donor states located near the conduction-band minimum (seen at different voltages for tunneling into and out of the states) and with a donorlike state derived from the accumulation layer.