Planar Ohmic Contacts to Al0.45Ga0.55N/Al0.3Ga0.7N High Electron Mobility Transistors

We present a low resistance, straightforward planar ohmic contact for Al 0.45 Ga 0.55 N/Al 0.3 Ga 0.7 N high electron mobility transistors. Five metal stacks (a/Al/b/Au; a = Ti, Zr, V, Nb/Ti; b = Ni, Mo, V) were evaluated at three individual annealing temperatures (850, 900, and 950°C). The Ti/Al/Ni/Au achieved the lowest specific contact resistance at a 900°C anneal temperature. Transmission electron microscopy analysis revealed a metal-semiconductor interface of Ti-Al-Au for an ohmic (900°C anneal) and a Schottky (850°C anneal) Ti/Al/Ni/Au stack. HEMTs were fabricated using the optimized recipe with resulting contacts that had room-temperature specific contact resistances of ρ c = 2.5 × 10 −5 Ω cm², sheet resistances of R SH = 3.9 kΩ/■, and maximum current densities of 75 mA/mm (at V GATE of 2 V). Electrical measurements from −50 to 200°C had decreasing specific contact resistance and increasing sheet resistance, with increasing temperature. These contacts enabled state-of-the-art performance of Al 0.45 Ga 0.55 N/Al 0.3 Ga 0.7 N HEMTs.