High-transconductance self-aligned AlGaN/GaN modulation-doped field-effect transistors with regrown ohmic contacts

Self-aligned AlGaN/GaN modulation-doped field-effect transistors (MODFETs) with high transconductances have been demonstrated on a sapphire substrate. Source and drain were selectively regrown with ∼1700 Å of $\mathrm{n-}\mathrm{GaN}$ adjacent to the gate electrode. Source resistance was reduced to 0.95 Ω mm from 1.4 to 1.8 Ω mm with conventional GaN-based MODFETs. These self-aligned devices show a record high value of extrinsic transconductance ∼400 mS/mm for AlGaN/GaN MODFETs with a gate length of 1.2 μm.