Negative conductance of an interdigital electrode structure on a semiconductor surface

It is shown that an interdigital electrode structure situated near a semiconductor surface may exhibit negative conductance if the drift velocity of the charge carriers in the semiconductor is sufficiently large. The conditions for obtaining this negative conductance are derived, and these theoretical predictions are compared with experimental results obtained for an interdigital electrode structure situated on an oxidized silicon surface. Negative conductance is observed in the frequency range from 25 to 75 MHz at a temperature of about 25 K, and the experimental data show good agreement with the theory. Finally the specific properties of different device geometries are considered with a view to the possibilities of operation at room temperature and at higher frequencies.