ATOM-RESOLVED IMAGING AND SPECTROSCOPY ON THE GAAS(001) SURFACE USING TUNNELING MICROSCOPY

Scanning tunneling microscopy and scanning tunneling spectroscopy have been used to investigate the structure and current-voltage [I(V)] characteristics of the molecular-beam epitaxially grown, As-rich Ga-As(001)-(2X4) surface. High-resolution images reveal a modulation in the topography of the individual arsenic dimers measured with the tunneling microscope in the constant current mode. The observed features are attributed to an increased tunneling probability out of the occupied electronic lone pair states of the As dimers. The I(V) spectroscopy performed on the (001) surface of low doped n-type GaAs samples differs considerably from the results obtained on the (110) surface of this semiconductor. This is attributed to band bending that is due to a lower doping concentration below the surface. The electrostatics involved in imaging with a tunneling microscope are described in a simple model, based on the depletion approximation, that accounts for the experimental results.