Photoinduced current properties of InAs-covered GaAs studied by scanning tunneling microscopy

We performed simultaneous imaging of photoinduced current and topography on an InAs-covered GaAs surface by scanning tunneling microscopy (STM) under modulated laser irradiation to investigate the difference in the electronic properties between quantum dots and a wetting layer. We also performed time-resolved tunneling current measurements to clarify the origin of the photoinduced effects on its surface. We observed a spiky transient current, resulting from photocarrier separation by a built-in field in the surface depletion layer. Images of the photoinduced current mainly originating from the surface depletion were obtained at a chopping frequency of 900 Hz, and both the photoinduced current images, and the current transients observed at this frequency reveal that the surface depletion is more suppressed under the dots than under the wetting layer.