• non-alloyed;
  • ultra-low contact resistance;
  • MIS;
  • ALD


This study investigates the development and application of Si-doped N-polar n+ GaN capping layers used for the reduction of ohmic contact and access resistances in inverted HEMTs. By applying an optimized n+ GaN capping layer to a standard undoped inverted HEMT, we find that non-alloyed Ti/Al/Ni/Au contacts demonstrate a very low ohmic contact resistance of 80 Ω-µm. To eliminate the n+ GaN shunting pathway in HEMT devices, we have used e-beam lithography and dry etching to define windows that establish an effective source-drain spacing. 0.3 µm gate-length inverted HEMTs with n+ GaN caps and 1 µm effective source-drain spacing were found to have a high maximum current density of 1.94 A/mm and an extrinsic transconductance of 335 mS/mm. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)