GaN-based light-emitting diodes provide higher performance in the short-wavelength part of the visible and ultraviolet spectrum than any other material system. However

there is still a great need for improvement of the extraction efficiency. Because many parts of emitting light of LED suffer absorption of the metal contacts and bond pads

also by active layer. So the employment of highly reflective metal ohmic contacts with a low contact resistance could substantially improve the GaN extraction efficiency of GaN-based LED

especially for vertical structure LED fabricated by laser lift-off process

which have more light output surface and high thermal conductivity than normal structure LED. The high reflectivity of omni-direction reflector is reported

that is

incorporation of Ag and Al onto the contact layers acting as a reflecting layer. Firstly

the reflectivity of the layers Ti/Ag

Al

Ni/Au/Ti/Ag and Ni/Au/Al were calculated through the theory of optical films. Then the reflectivity and contact characteristic of the GaN-based LED samples with these multi-layers on p-type GaN were measured. The result showed high omni-directional reflectors can be achieved over Ag-based films structure

and Al-based also

but the Ag-based films can provide higher reflectivity of 80%

which is better than that of Al-based film. The current-voltage curves showed low resistance on these contact layers except the Al direct on p-GaN. And the resistance of Ni/Au/Ti/Ag and Ni/Au/Al just depends on the annealed Ni/Au layers. Here the Ni/Au layers not only supply the ohmic contact but also the spreading the current. The conglomerate and oxidation of Ag film under high temperature are eliminated by introducing other Ni/Au cladding layers. Because the thickness of Ag is enough for high reflectivity so the additional layers after Ag also have no effect on the reflectivity. The good stability

low resistance and high reflectivity were obtained by two-step annealing methods. Then we applied the multi-layer Ni/Au/Ti/Ag/NiAu to vertical structure light emitting diodes (LED) by laser lift-off technology. The light output efficiency was improved significantly. The vertical structure LED with high reflective contact layer was fabricated successfully.