Enhancement of Drain Current by an AlN Spacer Layer Insertion in AlGaN/GaN High-Electron-Mobility Transistors with Si-Ion-Implanted Source/Drain Contacts

In AlGaN/GaN high-electron-mobility transistors (HEMTs) with an AlN spacer layer, which improves two-dimensional electron gas (2DEG) properties, it is important to decrease ohmic contact resistance because an AlN spacer layer with an extremely wide band gap decreases the contact resistance significantly. We employed Si ion implantation doping to solve this problem and successfully obtained a sufficiently low contact resistance equivalent to that of HEMT without an AlN spacer layer. In the fabricated AlGaN/AlN/GaN HEMTs with Si-ion-implanted source/drain contacts, as another effect of AlN spacer layer insertion, a reduction in the forward Schottky gate current was found, which made it possible to apply a high gate voltage in the transistor operation. Combined with the improvement in 2DEG properties, a marked enhancement in drain current density of 25–30% was observed.