Time evolution studies of the electrostatic surface potential of low-temperature-grown GaAs using electrostatic force microscopy.

An electrostatic force microscope was used to measure the electrostatic surface potential of low-temperature-grown GaAs (LTG:GaAs) before and after the removal of the native oxide layer. The surface potential of oxidized LTG:GaAs was found to be 450±50 mV with respect to a bare Au reference. This was consistent with the known work function of Au and energy bands of LTG:GaAs. After removal of the oxide layer using a chemical etch, the surface potential of the LTG:GaAs was found to evolve as time passed. The observed transient behavior depended both on the environment and the particular chemical etchant used to remove the native surface oxide, with time constants ranging from approximately 1 to 10 h. The behavior can be explained in terms of the decay of a charge sheet or dipole at the surface. The experiments provide insights into the surface electrical properties of LTG:GaAs and, indirectly, stoichiometric at critical stages of typical device fabrication processes. [ABSTRACT FROM AUTHOR]