TiN-based Au-free Ohmic contact on n-AlGaN and fabrication of high efficiency DUV-LEDs.

We propose an Au-free Ti/Al/TiN Ohmic contact on an n-type Al0.57Ga0.43N epitaxial layer and utilize it in deep-ultraviolet light-emitting diodes with improved efficiency. The surface morphology, chemical stoichiometry, and electrical performance of the proposed contact are thoroughly investigated and compared with those of conventional Ti/Al/Ni/Au electrodes. The Ti/Al/TiN stack exhibits a specific contact resistivity of 3.41 × 10-4 Ω·cm2 at optimized annealing conditions, which is 26.5% lower than that of the conventional Ti/Al/Ni/Au stack (4.64 × 10-4 Ω·cm2). A smoother surface morphology and the absence of phase separation are identified in the proposed Ti/Al/TiN design, attributed to the low diffusivity of TiN into other metal alloys and its strong thermal stability as a binary compound.