AlGaN/GaN Heterostructure Field-Effect Transistors on Fe-Doped GaN Substrates with High Breakdown Voltage

AlGaN/GaN heterostructure field-effect transistors (HFETs) were fabricated by metalorganic vapor phase epitaxy (MOPVE) on c-plane Fe-doped GaN (GaN:Fe) substrates with different growth conditions of GaN buffer layers. The GaN buffer layers were grown at a V/III ratio of 272 at 300 Torr to realize highly resistive GaN buffer layers with automatic carbon doping. HFETs with carbon-doped GaN buffer layers showed the best characteristics among all the samples in this study. The carbon concentration was 5×1016 cm-3. In the sample with a gate-drain length of 50 µm, the off-state breakdown voltage was 2 kV or higher and the on-resistance was 18.5 mΩ·cm2. We found that the carbon-doped GaN buffer layers are necessary for high breakdown voltages even using semi-insulating GaN:Fe substrates.