Semiconductor light emitting device having a silver p-contact
View Patent ↗A light emitting device is constructed on a substrate. The device includes an n-type semiconductor layer in contact with the substrate, an active layer for generating light, the active layer being in electrical contact with the n-type semiconductor layer. A p-type semiconductor layer is in electrical contact with the active layer, and a p-electrode is in electrical contact with the p-type semiconductor layer. The p-electrode includes a layer of silver in contact with the p-type semiconductor layer. A bonding layer is formed overlying the silver layer to make an electrical connection to the silver layer. The silver layer may be thin and transparent or thicker (greater than 20 nm) and reflective.
1. A light emitting device comprising:
a substrate;
an n-type semiconductor layer;
an active layer for generating light, said active layer being in electrical contact with said n-type semiconducting layer;
a p-type semiconductor layer in electrical contact with said active layer; and
a p-electrode in electrical contact with said p-type semiconductor layer, said p-electrode comprising:
at least a layer of silver having a thickness sufficient to reflect greater than 50% of light incident thereon, wherein a portion of said generated light exits said device through said substrate after being reflected from said p-electrode;
a bonding layer in electrical contact with said layer of silver for making electrical connections to said layer of silver; and
a fixation layer overlying at least a portion of said layer of silver, wherein the fixation layer is conductive.
2. The light emitting device of claim 1 wherein said n-type semiconductor layer and said p-type semiconductor layer comprise group III nitride semiconducting materials.
3. The light emitting device of claim 1 wherein said silver layer is greater than or equal to 20 nm in thickness.
4. The light emitting device of claim 1 wherein said fixation layer comprises a metal.
5. The light emitting device of claim 4 wherein said fixation layer comprises a metal chosen from the group consisting of nickel, palladium, and platinum.
6. The light emitting device of claim 1 wherein said bonding layer comprises a metal chosen from the group consisting of gold, nickel, aluminum, and indium.
7. The light emitting device of claim 1 wherein said bonding layer covers less than half of said layer of silver.
8. The light emitting device of claim 1 wherein said bonding layer is a multi-layered structure.
9. The light emitting device of claim 1 wherein said fixation layer is disposed between said bonding layer and said layer of silver, said fixation layer providing an electrical path between said bonding layer and said layer of silver, said fixation layer serving as a diffusion barrier layer for preventing constituents from said bonding layer from interdiffusing with said layer of silver.
10. The light emitting device of claim 9 wherein said fixation layer comprises a metal.
11. The light emitting device of claim 10 wherein said fixation layer comprises nickel.
12. The light emitting device of claim 9 wherein said fixation layer encapsulates said layer of silver.
13. The light emitting device of claim 1 further comprising:
an n-electrode comprising a layer of electrically conducting material in electrical contact with said n-type semiconductor layer; and
a package having first and second conductors thereon electrically connected to said p-electrode and said n-electrode, respectively.
14. A light emitting device comprising:
a substrate;
an n-type semiconductor layer;
an active layer for generating light, said active layer being in electrical contact with said n-type semiconducting layer;
a p-type semiconductor layer in electrical contact with said active layer; and
a p-electrode in electrical contact with said p-type semiconductor layer, said p-electrode comprising:
at least a substantially transparent layer of silver;
a bonding layer in electrical contact with said layer of silver for making electrical connections to said layer of silver; and
a fixation layer overlying said layer of silver, wherein the fixation layer is conductive.