Electrostatic force microscopy studies of surface defects on GaAs/Ge films

We apply electrostatic force microscopy (EFM) to study defects in GaAs film s grown on Ge. On a GaAs film with surface antiphase boundaries (APBs), we reproducibly measure the surface contact potential (SCP) at the APBs to be (30+/-5) mV higher than that of the domains, due to the surface Fermi level at APBs being pinned closer to the valence band maximum. On a thick film w hich contains buried APBs and wedge-shaped depressions on the surface, we f ind that the SCP of the wedge-shaped depressions is (25+/-5) mV lower than that of the GaAs surface. Hence, these wedge-shaped depressions have defect electronic states different from those of APBs. The capacitance gradient ( partial derivative C/partial derivative z) contrasts on the two samples are also shown to arise from different origins. Factors that can affect the me asured SCP and partial derivative C/partial derivative z values are discuss ed. We demonstrate a new application of EFM to distinguish different types of defects by measuring variations in relative SCP (thus the work function or position of Fermi level) and/or partial derivative C/partial derivative z on sample surfaces. The spatial resolutions of SCP and partial derivative C/partial derivative z are 30 nm, limited by the tip size. (C) 1999 Americ an Institute of Physics. [S0021-8979(99)00405-3].