AlGaN Channel High Electron Mobility Transistors with an Al_xGa_1-xN/GaN Composite Buffer Layer

We report an AlGaN channel high electron mobility transistor (HEMT) on a sapphire substrate with a 1000-nm Al_xGa_1-xN (x=0–0.18)/GaN composite buffer layer. With a significant improvement of crystal quality, the device features a high product of n_s·μ_n. The AlGaN channel HEMTs presented show improved performance with respect to the conventional AlGaN channel HEMTs, including the on-resistance reduced from 31.2 to 8.1 Ω·mm, saturation drain current at 2 V gate bias promoted from 218 to 540 mA/mm, peak transconductance at 10 V drain bias promoted from 100 to a state-of-the-art value of 174 mS/mm, and reverse gate leakage current reduced from 1.85×10^-3 to 2.15×10^-5 mA/mm at V_GD=-20 V.