Strain-induced work function changes in Ge nano-stripes on Si (001) studied by energy-filtered photoelectron emission microscopy

Investigation of Ge nanostructures on Si(001) is of great interest for high-mobility Ge MOSFETs and potential applications in near-infrared photodetection. In this paper the experimental investigation of the strain state of Ge nano-stripes fabricated by selective epitaxial growth of Ge on a Si(001) substrate patterned with 100nm wide trenches is presented. Energy-filtered photoelectron emission microscopy has been used to spatially map with nanoscale resolution the strain-induced change in the electron work function of the nano-stripes. Strain information has been obtained by comparing the experimentally measured work function with a simple model developed within the framework of the potential deformation theory. A tensile deformation of ~ 0.4% has been found in the nano-stripes. The origin of this strain state is attributed to the joint contribution of the plastic relaxation induced by misfit dislocations and the coherency constraints imposed by the Si substrate, as supported by finite element method (FEM) simulations