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

Abstract

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 ${\mathrm{CuGaSe}}_2$ the experiments demonstrate differences as low as 30 meV between (102) and (111) oriented surfaces and up to 255 meV between $\text{(1̄1̄2̄)}$ and (110) surfaces. This influences the band bending of solar cell heterostructures and consequently also the solar power conversion efficiency.