Imaging of local charge density in an InAs/GaAs two-dimensional heterostructure by scanning tunneling microscopy

We have studied the bias-voltage dependence of constant-current images obtained by scanning tunneling microscopy (STM) at 4.8 K on an InAs thin film grown on GaAs (111)A substrates. In-plane surface-height variation as large as 0.1-0.2 nm was detected on the step-free region, only with the negative sample voltages higher than -0.6 V. Because the bias condition corresponds to the tunneling of electrons accumulated in the InAs film to the STM tip, we believe that the image reflects the local electron density in InAs/GaAs two-dimensional heterostructures.