Surface Varactors which can Give Positive and Negative Capacitances

In this work a crystal of 7·3 ohm metre p-type silicon with 0·1 mm thin mica spacer sandwitched between two field plates suitably biased has been used to offer positive and negative capacitances below 5 MHz. The polarity of the capacitance and its magnitude could be changed with polarity and magnitude of field voltage. The results have been interpreted in terms of surface and bulk effects in the sample.