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.

Figure optionsDownload as PowerPoint slide