The role of Ni and Au on transparent film of blue LEDs

The role of Ni, Au on transparent film of light emitting diodes (LEDs) has been studied by I–V and optical transmission measurement. When fixing Ni layer at 5 nm, the thickness of Au layer in the Ni/Au bilayer was changed from 2 to 20 nm, the forward voltage (Vf) of LEDs decreased rapidly with increasing the thickness of Au layer. When fixing Ni layer at 10 nm, the thickness of Ni layer in the Ni/Au bilayer was changed from 2 to 20 nm, the results show that the Vf does not monotonically decrease with increasing the thickness of Ni layer. It is found that Au layer play a role of spreading the injection current while the Ni layer play a role of reducing the Schottky barrier height. The effect of thermal treatment on the behavior of the ohmic contact of Ni/Au to p-GaN contacts was also investigated by I–V measurement. It is found that it exists a reversible process of contact resistance when the Ni/Au to p-type GaN contacts is annealed in air and N2 ambient alternatively.