MICROWAVE IMPEDANCE MEASUREMENTS ON RESONANT-TUNNELING DIODES WITH ASYMMETRIC SPACER LAYERS

Scattering parameters (S parameters) have been measured up to 40GHz on GaAs/AlAs resonant tunneling diodes containing asymmetric spacer laye rs. On-wafer microwave probing techniques were used. A hysteresis was observed in the vicinity of the negative differential resistance (NDR) region. Unlike the one observed in de current-voltage measurements, t his hysteresis was not affected by oscillations and believed to be int rinsic. The impedance data has been fitted to a lumped equivalent circ uit model and capacitance-voltage (C-V) characteristic extracted. In a ddition to the already reported capacitance peak in the NDR region, a smaller peak at a lower voltage was found. In comparison to the self-c onsistent calculation, the smaller peak is due to the electrons discha rging from accumulation region between the emitter barrier and the cat hode spacer layer. The C-V result agrees qualitatively with the theore tical calculation. It supports the theoretical argument that the negat ive conductance can be increased by increasing the cathode spacer laye r, however, there is also an increase in capacitance and the cutoff fr equency may be reduced.