For nitride heterojunction field-effect transistors, the heterojunction forming the electron barrier has to be designed based on trade-offs between lattice mismatch, two-dimensional electron gas concentration, and alloy scattering. In this work, we study the use of a superlattice-based barrier which effectively increases the heterojunction barrier while reducing the lattice mismatch and alloy scattering. The structure studied consists of a five-period superlattice of 2 nm Al0.2Ga0.8N + 2 nm Al0.3Ga0.7N on GaN grown using metalorganic chemical vapor deposition on a 6 H SiC conducting substrate. The barriers of the second and third period of the superlattice are Si-doped to give the effect of modulation doping. Devices fabricated from the structure exhibit a high g. of similar to299 mS/mm and an I-ds max of 0.85 A/mm. To our knowledge, this is the first investigation of the use of superlattice structure for improvement of the barrier properties in a nitride HFET. (C) 2004 Elsevier B.V. All rights reserved.