High-reflectance ohmic contacts to p-GaN are the key for Flip-chip ultra-violet light emitting diode (UV-LED) to improve the external quantum efficiency (EQE)

so the kinds of metal or alloy film both ohmic contact and the reflector of light are important to choose the appropriate high-reflectance and low-resistance ohmic contact to p-type GaN. The GaN-based LED samples used were grown by Metalorganic Chemical Vapor Deposition (MOCVD). Four different metal films were deposited on the surfaces of p-GaN and annealed Ni/Au alloy. The thickness of these metal films varied from 30 nm to 840 nm. The reflectance and transmittance of the samples were mea-sured by WGS-9 system. The 2θ scans XRD and surface AFM images of the samples were also observed. As results

when the films' thickness under the 130 nm the reflectance of Ag-deposited samples increased with the increasing thickness and the transmittance decreased at wavelength of 400 nm. The reason of the increasing of reflectance is the reduction of the light transmitted through the films. When the films' thickness over 130 nm

the reflectance of Ag-deposited samples decreasing. From the results of XRD and AFM

the metal film formed multi-layers film and the roughness

R

a

and

R

q

increased with the increasing thickness. It is suggested that the diffusion of the multi-layers films is the main reason of reduction of reflectance with the films thickness increasing. Other metal films show the same characteristics as the Ag-deposited films. From the result of reflectance

Al and Ag are the suitable candidates for the reflector

but it is reported that the single Al or Ag films don't make good ohmic contacts on p-GaN. So a thin annealed Ni/Au is adopted to interspersed between the Al or Ag reflector and the p-GaN in order to provide efficient hole injection into the device. From the results of reflectance and

I

-

V

curves of Ni/Au/Ag and Ni/Au/Al

the

I

-

V

characteristics of Ni/Au/Ag and Ni/Au/Al contacts are similar to this of Ni/Au annealed. However the reflectance of Ni/Au/Ag and Ni/Au/Al contacts is three times higher than that of Ni/Au at wavelength of 400 nm. These results demonstrated that Ni/Au/Ag and Ni/Au/Al can be used as high-reflectance and low-resistance p-GaN ohmic contacts for flip-chip UV-LEDs