Photoabsorption characterization on surface InAs nanostructures using light-illuminated scanning tunneling microscopy

We characterized surface InAs nanostructures grown on a GaAs vicinal substrate by using scanning tunneling microscopy (STM) under light illumination. In local photoinduced current imaging with a DC bias voltage, the photoabsorption signals on InAs nanowires could not be detected when the illuminated photon energy was adjusted between the band gaps of GaAs and InAs, due to electrical isolation of the surface InAs from the conductive substrate. On the other hand, imaging an optical response of differential conductance with AC bias modulation revealed a clear contrast between InAs nanowires and the surrounding GaAs region without the generation of photocarriers in the underlying GaAs.