Engineering the (In, Al, Ga)N back-barrier to achieve high channel-conductivity for extremely scaled channel-thicknesses in N-polar GaN high-electron-mobility-transistors

Scaling down the channel-thickness (tch) in GaN/(In, Al, Ga)N high-electron-mobility-transistors (HEMTs) is essential to eliminating short-channel effects in sub 100 nm gate length HEMTs. However, this scaling can degrade both charge density (ns) and mobility (μ), thereby reducing channel-conductivity. In this study, the back-barrier design in N-polar GaN/(In, Al, Ga)N was engineered to achieve highly conductive-channels with tch < 5-nm using metal organic chemical vapor deposition. Compositional-grading was found to be the most effective approach in reducing channel-conductivity for structures with tch ∼ 3-nm. For a HEMT with 3-nm-thick-channel, a sheet-resistance of 329 Ω/◻ and a peak-transconductance of 718 mS/mm were demonstrated.