Ultra-low ohmic contacts to N-polar GaN HEMTs by In(Ga)N based source-drain regrowth by Plasma MBE

摘要

For highly scaled submicron HEMTs, ultra-low ohmic contact resistances are required to reduce the drop in intrinsic gm (transconductance) of the device to obtain higher ft and fmax. Moreover, for self-aligned HEMT structures, reducing the ohmic contact resistance becomes the most pivotal issue in attaining better small signal performance and cutoff frequencies. N-face GaNHEMTs, growth direction C00®*), offer a natural advantage for this issue over Ga-face GaN HEMTs, since the ohmic contact to the 2DEG is made through GaN, with lesser band-gap, than AlGaN. In this work we extend the advantage of N-face HEMTs by making use of polarization induced charges through re-growth of graded InGaN ohmic contact regions, to obtain ultra-low and record ohmic contact resistances. An ohmic contact resistance of 27 il um was obtained to a N-face GaN HEMT by regrowth of graded InGaN capped with a thin layer of InN by plasma MBE. To the best of our knowledge, these are the lowest ever reported ohmic contact resistances to a GaN 2DEG.