Imaging of Friedel oscillations at epitaxially grown InAs(111)A surfaces using scanning tunneling microscopy

The low-temperature scanning tunneling microscopy study of the local density of states (LDOS) was performed at the epitaxially grown InAs surface on the GaAs(111)A substrate. In the simultaneously mapped dl/dV images, LDOS oscillation patterns were clearly imaged and showed bias voltage dependence at surface defect sites. Clear oscillatory LDOS patterns made of concentric circles were observed due to Friedel oscillations at an isolated defect. It is found that the main wave feature is determined by semiconductor two-dimensional electron gas (2DEG) states in the surface accumulation layer. In the semiconductor nanostructures, symmetric and regular patterns are observed. Furthermore, zero-dimensional states were observed in the small triangular cages.