Voltage-dependent scanning tunneling microscopy imaging of semiconductor surfaces

We present voltage-dependent scanning tunneling microscopy (STM) data from various semiconductor surfaces. Different techniques for acquiring the data are demonstrated, and the interpretation of spectroscopic data is discussed. For the Si(111)2x1, GaAs(110), and O/ GaAs(110) surfaces, we find that the voltage dependence of constant-current contours provides the most direct method for understanding the electronic and geometric structure of the surface. For the case of oxygen on «-type GaAs, we observe a reversal in the constant-current contours when the polarity of the bias voltage is reversed, which is interpreted in terms of band bending due to a negatively charged adsorbate. Theoretical calculations for a screened Coulomb potential are shown to agree with the observed reversal in the STM contours of the adsorbed oxygen. © 1988, American Vacuum Society. All rights reserved.