VOLTAGE-DEPENDENT SCANNING TUNNELING MICROSCOPY IMAGE OF THE GAINAS INP MULTIQUANTUM WELL STRUCTURE

The cross-sectional (110) surface of the GaInAs/InP multiquantum well (MQW) structure was observed by scanning tunneling microscopy (STM). In this STM observation using the constant-current mode, it was found that the corrugation amplitude of the MQW image sharply increased upon decreasing the applied positive bias voltage of the tip. Using a simple free-electron model, this phenomenon is explained: Due to the difference of the valence-band energy levels in the well and the barrier layers, the number of valence electrons above the Fermi level of the tip is different between these layers; the ratio Of the tunneling current (I(well)/I(barrier)) becomes larger when the Fermi level of the tip is closer to the valence-band energy level in the barrier layers, resulting in a larger corrugation amplitude of the MQW image.