We report an experimental and theoretical study of electron transport
in short (similar to 200 nm) Al0.265Ga0.735As/GaAs n-type superlattice
s. In order to make the results of this investigation relevant to quan
tum-well infrared photodetectors, our devices had wide barriers at the
contacts to reduce dark current. Transport involved both thermal and
tunnelling components, in general, throughout the temperature range 77
-300 K. At a critical high current superlattice domain formation assoc
iated with tunnelling negative differential resistance was observed in
some of our devices. Standard theoretical expressions were used for t
he thermal and tunnelling components in each section of the device. At
higher biases Fowler-Nordheim tunnelling was used to explain the rapi
d increase in current with voltage. The critical roles of well capture
, confined level broadening and built-in voltages were identified. Sat
isfactory agreement between theory and experiment was obtained and thi
s allowed an estimate of level broadening to be made.