MILLIMETER-WAVE NEGATIVE DIFFERENTIAL CONDUCTANCE IN GAINAS ALINAS SEMICONDUCTOR SUPERLATTICES/

We report microwave and temporal measurements on nonlinear transport i n GaInAs/AlInAs superlattice n(+) n(-) n(+) diodes. The superlattices have wide minibands, wider than 80 meV. The microwave experiments are performed for 0-65 GHz. The diodes exhibit reflection gain up to 65 GH z over a bias-dependent Hakki resonance. The temporal experiments use electro-optic sampling to push the measurement range beyond 200 GHz. H armonics of the fundamental Hakki resonance are observed up to order t hree at 150 GHz. A simple admittance model for negative differential c onductance devices accounts for the results in both experimental appro aches. They are in agreement with miniband transport and demonstrate s uperlattice negative differential conductance far in the millimetre-wa ve domain. (C) 1998 Academic Press Limited.