Impact of the low temperature ohmic contact process on DC and forward gate bias stress operation of GaN HEMT devices
In AlGaN/GaN high electron mobility transistors (HEMTs), high temperature processes (such as ohmic annealing with >800°C value) could deform the crystal structure and induce trap states within the bulk and surface. Expanded defect densities cause crucial problems, such as threshold voltage ( Vth ) instability, current collapse, and high leakages. In this work, a low temperature ohmic contact process (630°C, 10 minutes) is adopted with recess etch, and contact resistances <0.1Ω ⋅ mm with low sheet resistances are achieved. The positive impact of this low thermal budget process on surface morphology, DC operation, long-term stability, and forward gate bias stress of the device is studied.