In this paper, we present recessed AIGaN/GaN heterojunction field-effect transistors (HFETs) with lattice-matched InAlGaN capping layers, which reduce both ohmic contact resistance and series resistance between the AlGaN and the capping layer. The lattice-matched alloy epitaxial layer with both In and Al high compositions are successfully grown by metal-organic chemical vapor deposition. The grown lattice-matched In0.09Al0.32Ga 0.59N capping layer has close total polarization and bandgap to those of the underlying Al0.26Ga0.74N layer. The balanced polarization eliminates the depletion of electrons at the In 0.09Al0.32Ga0.59N/Al0.26Ga 0.74N interface, which can reduce the series resistance across it. It is also noted that the fabricated HFET exhibits very low ohmic contact re: sistance of 1.0 × 10-6 Ω ·cm2 or less. Detailed analysis of the source resistance reveals that the series resistance at the In0.09Al0.32Ga0.59N/Al 0.26Ga0.74N interface is one fifth as low as the resistance at the conventional GaN/Al0.26 Ga0.74N interface.
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