Negative-Capacitance Effect in Forward-Biased Metal Oxide Semiconductor Tunnel Diodes (MOSTD)

A negative capacitance (NC) effect in metal oxide semiconductor tunnel diodes (MOSTD) is reported. The phenomenon is observed with forward-biased minority carrier type MOSTDs with low measurement frequencies. Enhancements of the effect with the higher substrate resistivity and with the increase of the minority carrier injection indicate that the effect arises from conductivity modulation in the substrate. The equivalent circuit consisting of a parallel “inductor”-resistor pair in series with the ordinary equivalent circuit of a MOSTD biased in accumulation is found to be a good first order representation of the measured impedance spectra.