High-resolution work function imaging of single grains of semiconductor surfaces

The size reduction of modern electronic devices creates a growing demand for characterization tools to determine material properties on a nanometer scale. The Kelvin probe force microscope is designed to obtain laterally resolved images of the sample’s work function. Using a setup in ultrahigh vacuum, we were able to distinguish work function variations for differently oriented crystal facets of single grains on a semiconductor surface. For the tetragonal solar cell material CuGaSe2 the experiments demonstrate differences as low as 30 meV between (102) and (111) oriented surfaces and up to 255 meV between (1̄1̄2̄) and (110) surfaces. This influences the band bending of solar cell heterostructures and consequently also the solar power conversion efficiency.