Self-aligned-gate AlGaN/GaN heterostructure field-effect transistor with titanium nitride gate

Self-aligned-gate heterostructure field-effect transistor (HFET) is fabricated using a wet-etching method. Titanium nitride (TiN) is one kind of thermal stable material which can be used as the gate electrode. A Ti/Au cap layer is fixed on the gate and acts as an etching mask. Then the T-shaped gate is automatically formed through over-etching the TiN layer in 30% H2O2 solution at 95 degrees C. After treating the ohmic region with an inductively coupled plasma (ICP) method, an Al layer is sputtered as an ohmic electrode. The ohmic contact resistance is approximately 0.3 Omega.mm after annealing at a low-temperature of 575 degrees C in N-2 ambient for 1 min. The TiN gate leakage current is only 10(-8) A after the low-temperature ohmic process. The access region length of the self-aligned-gate (SAG) HFET was reduced from 2 mu m to 0.3 mu m compared with that of the gate-first HFET. The output current density and transconductance of the device which has the same gate length and width are also increased.