Oscillations up to 420 GHz in GaAs/AlAs resonant tunneling diodes

We report room-temperature oscillations up to frequencies of 420 GHz in a GaAs resonant tunneling diode containing two 1.1-nm-thick AlAs barriers. These results are consistent with a recently proposed equivalent circuit model for these diodes in which an inductance accounts for the temporal delay associated with the quasibound-state lifetime. They are also in accordance with a generalized impedance model, described here, that includes the effect of the transit time delay across the depletion layer. Although the peak-to-valley ratio of the 420 GHz diode is only 1.5:1 at room temperature, we show that its speed is limited by the parasitic series resistance rather than by the low negative conductance. A threefold reduction in this resistance, along with a comparable increase in the peak-to-valley ratio, should allow oscillations up to about 1 THz.