T. Wei et al., MICROWAVE IMPEDANCE MEASUREMENTS ON RESONANT-TUNNELING DIODES WITH ASYMMETRIC SPACER LAYERS, Superlattices and microstructures, 16(2), 1994, pp. 191-195
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.