Thermal stability improvement by using Pd ∕ NiO ∕ Al ∕ Ti ∕ Au reflective ohmic contacts to p -GaN for flip-chip ultraviolet light-emitting diodes

• Published in: Applied physics letters 2006-02, Vol.88 (6), p.062113-062113-3
• Main Authors: Pan, Chang-Chi, Chen, Guan-Ting, Hsu, Wen-Jay, Lin, Chih-Wei, Chyi, Jen-Inn
• Format: Article
• Language: English
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.2173245

The thermal stability, optical reflectivity, and contact resistivity of Pd ∕ NiO ∕ Al ∕ Ti ∕ Au ohmic contacts to p -type GaN were investigated. In contrast to Pd ∕ Ni ∕ Al ∕ Ti ∕ Au counterparts, the ohmic contacts Pd ∕ NiO ∕ Al ∕ Ti ∕ Au retained their specific contact resistivity ( < 3.3 × 10 − 2 Ω cm 2 ) and high reflectivity ( > 75 % @ 370 nm) after a long thermal aging at 200°C for 100 h in nitrogen ambient. According to the results of the secondary ion mass spectroscopy in-depth profiles study, it is found that the NiO layer is more transparent and a better diffusion barrier than Ni to prevent the penetration of upper metals into p -type GaN during thermal treatment.