Electrostatic force characterization on InAs dot-covered n-type (001) GaAssurfaces by contact-mode atomic force microscopy with a conductive tip

We performed atomic force microscopy in contact mode while applying an ac b ias voltage between a conductive tip and a sample to characterize near surf ace band structures of InAs-covered n-type (001) GaAs, where self-assembled dot structures were formed. Electrostatic force of less than 10 pN was det ectable, and clear electrostatic force images and topographic images were s imultaneously obtained with lateral resolution higher than 20 nm. The elect rostatic force images from single and double frequency components reveal th at the gap width between the tip and the conductive region under the dot-co vered area of the sample is smaller and is less modulated by the bias volta ge than under the wetting layer. The results indicate that surface depletio n is more suppressed beneath the dots. (C) 1999 American Institute of Physi cs. [S0003-6951(99)00930-4].