Scanning frequency comb microscopy (SFCM): A new method showing promise for high-resolution carrier profiling in semiconductors

A microwave frequency comb (MFC) with hundreds of measurable harmonics is superimposed on the DC tunneling current in a scanning tunneling microscope by focusing a mode-locked ultrafast laser on the tunneling junction. Two methods for carrier profiling of semiconductors by hyperspectral measurements with the MFC are considered. The first method, analogous to scanning capacitance microscopy (SCM), would require high-precision measurements because resonant detection, required in SCM, is not practical with the MFC. The second method, analogous to scanning spreading resistance microscopy (SSRM), is more sensitive to the carrier concentration and shows promise for achieving sub-nm resolution which is needed by the semiconductor industry with sub-10 nm lithography.