Thermal stability of multilayer Ti2AlN-based ohmic contacts to n-GaN in ambient air

•Ti2AlN-based ohmic contacts to n-GaN (rc = 8 × 10−4 Ω cm2) aged in ambient air.•Ohmic characteristics retained after 100-h aging at 300 °C, 400 °C and 500 °C.•Rms surface roughness of 2 nm and ∼5 nm after forming and aging, respectively.•Roughness order of magnitude lower than for conventional Ti/Al/Ni/Au metallizations.

A multilayer Ti/Al/TiN/Ti/Al/TiN/Ti/Al/TiN metallization scheme is applied as an ohmic contact to n-GaN (n = 1017 cm−3). After formation of the contact through RTP at 600 °C for 6 min in Ar flow a Ti2AlN layer is created at the interface to n-GaN and Ti/Al layers form AlTi. The specific contact resistance of the as-formed contact is 7.4 × 10-4 Ω cm2. The contact remains ohmic and morphologically unaltered for annealing at 300 °C, 400 °C and 500 °C in ambient air for 100 h each and its resistivity rises to around 1.1 × 10−3 Ω cm2. This stability on one hand can be attributed to Ti2AlN MAX phase presence at the interface which inhibits excessive decomposition of GaN and thus confines the reaction between n-GaN and the metallization, and on the other to the presence of several TiN films in the metallization scheme, which are known to be diffusion barriers.

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