Fabrication and Performance of Au-Free AlGaN/GaN-on-Silicon Power Devices With Al2O3 and Si3N4/Al2O3 Gate Dielectrics

Au-free GaN-based metal-insulator-semiconductor high electron-mobility transistors grown on 150-mm Si substrates are reported. The device characteristics for three different processes are compared: an ohmic-first and a gate-first process with Al2O3-only as gate dielectric and a novel approach with a bilayer gate dielectric stack consisting of Si3N4 and Al2O3. The Si3N4 layer was deposited in situ in the metal-organic chemical vapor deposition reactor in the same growth sequence as the rest of the epilayer stack and the Al2O3 layer was deposited ex situ by atomic layer deposition. Only the process with the bilayer gate dielectric results in robust devices with a breakdown voltage >600 V. The ohmic contact resistance for Au-free Ti/Al/W metallization scheme is <1 Omega.mm. The devices show high maximum output current density (>0.4 A/mm); and low gate and drain leakage (<10(-10) A/mm). The maximum pulsed mode drain-source current of power bars with 20 mm gate width is 8 A. The specific on-state resistance is 2.9 m Omega.cm(2).