Imaging of Friedel Oscillation Patterns of Two-Dimensionally Accumulated Electrons at Epitaxially Grown InAs(111)ASurfaces

The local density of states (LDOS) at the epitaxially grown InAs surface on a GaAs(111) $A$ substrate were characterized using low-temperature scanning tunneling microscopy. Using $dI/dV$ signal mapping, LDOS standing waves were clearly imaged at point defects and within nanostructures. Measurement of the wavelength as a function of bias voltage showed a nonparabolic dispersion relation for the conduction band. The observed wave features originate from the Friedel oscillations of the two-dimensional electron gas in the semiconductor surface accumulation layer.