TUNNELING SPECTROSCOPY ON THE GAAS(110) SURFACE - EFFECT OF DOPANT CONCENTRATION

Scanning tunneling spectroscopy has been used to investigate the effect of doping concentration on the current-voltage characteristics of the GaAs(110) surface. For a fixed tip-sample separation, the conductivity gap is found to increase as the doping concentration is reduced. The results are compared with the predictions of a one-dimensional planar tunneling model which takes the tip-induced band-bending into account. Good agreement between the experiment and the calculations is achieved in the high-doping regime. The disagreement at lower doping levels suggests the absence of a complete equilibrium between the minority carriers at the surface and the majority carriers in the bulk, as well as the importance of dimensionality in describing the tip-sample interaction.