The frequency capabilities of integrated In0.53Ga0.47As/AlAs resonant
tunnelling diodes have been investigated by successfully tracking thei
r resistive cutoff frequencies when tile samples are biased in the neg
ative differential conductance region. The devices exhibit extremely h
igh peak current density (J(p) = 175kAcm(2)) and very low series resis
tance (6 x 10(-7)Omega cm(2)) so that submillimetre wave operation can
be expected.