Dual Microscopes Illuminate Electronic Switching Speeds

GAITHERSBURG, Md., Sept. 29 -- Although silicon is still the mainstay of the semiconductor industry, a new method may put materials like gallium nitride and silicon carbide into wider use in scanning semiconductors for defects. Such advanced semiconductor materials can operate at higher voltages and provide faster switching speeds, an important characteristic in determining how fast a semiconductor circuit can process information.

Joseph Kopanski, a researcher for the National Institute of Standards and Technology, and Korean guest researcher G. H. Buh combined an atomic force microscope (AFM) with a scanning capacitance microscope, then added custom software and a simple on/off switch for the AFM’s positioning laser. The result is an instrument that can measure how fast a material generates electrical charges and then map those speeds in sections, at least for gallium nitride, that are only about 100 nanometers square. Current methods for measuring switching speed (carrier lifetime) produce only bulk averages.

According to Joseph Kopanski, the system allows quick scanning of semiconductor wafers for defects that otherwise may not be found until an expensive device has already been built on the material. Most defects in semiconductors (i.e., sections with missing atoms) are presumed to slow down the speed that charges move through a material. Kopanski said further research using the new technique should determine if this assumption is correct. A patent application is pending on the technique.

The work is described in the the Sept. 22 issue of Applied Physics Letters.

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