Noncontact Measurement of Physical Properties of Semiconductors by Terahertz Time-Domain Spectroscopic Ellipsometry
Through the global promotion of the Green New Deal, the market for power semiconductors which can improve the efficiency of power conversion has been expanding. Since wide gap semiconductors such as GaN and SiC have a withstand voltage ten times as high as Si and higher electron mobility compared with Si, they have received a great deal of attention as a material for next generation low loss power semiconductors. On the other hand, these materials have a number of weak points, such as dislocationwhere maintaining substrate quality at higher levels is an important challenge for improving the production yield of finished products.
Grasping electrical-physical properties which exert influence on device properties such as carrier density and mobility is vitally important. Hall or cyclic voltammetry measurement is required to gain these physical properties by forming ohmic electrodes on sample material. These measurements are based on destructive inspection, which precludes the measurement of material used for devices. Under such circumstances, a method which can measure physical properties accurately without contacting a material is eagerly sought.
Taking this opportunity, the research group attempted experimental measurements of physical properties without contacting semiconductor materials utilizing THz light based on the principle that interactions between light and matter are reflected in dielectric properties. When light enters a semiconductor, free electrons are activated through resonating with the electromagnetic field of light; and in the THz band, such responses are reflected in dielectric properties. These dielectric properties can be expressed in a model function known as the Drude model, and change depending on electrical-physical properties such as carrier density or mobility. This method can gain the electric parameters mentioned above without contacting a sample material by measuring dielectric properties in the THz band.