Ring-dot impedance measurement, a simple technique for measuring inversion-layer conductance in semiconductors

Impedance measurements utilizing evaporated ring-dot metal-oxide-semiconductor (MOS) structures are shown to give accurate values of sheet conductance of inversion layers. The well-defined geometry simplifies evaluation of experimentally measured quantities. The results obtained are shown to be independent of the geometry of the test structures and of frequency. Limitations of the technique due to shunting by the substrate are discussed. It is found that for a channel sheet resistance of 10
⁴
ohms the technique can be used for substrate impurity concentrations up to 5 × 10
¹⁶
cm
^-3
in silicon.