Transparent electrode for semiconductor light-emitting device
A transparent electrode for a gallium nitride-based compound semiconductor light-emitting device includes a p-type semiconductor layer ( 5 ), a contact metal layer ( 1 ) formed by ohmic contact on the p-type semiconductor layer, an current diffusion layer ( 12 ) formed on the contact metal layer and having a lower magnitude of resistivity on the plane of the transparent electrode than the contact metal, and a bonding pad ( 13 ) formed on the current diffusion layer. The transparent electrode is at an advantage in widening the surface of light emission in the p-type semiconductor layer, decreasing the operation voltage in the forward direction, and enabling the bonding pad to provide excellent adhesive strength.
1. A transparent electrode for a gallium nitride-based compound semiconductor light-emitting device having a p-type semiconductor layer, wherein the transparent electrode comprises a contact metal layer formed by ohmic contact on the p-type semiconductor layer, a current diffusion layer formed on the contact metal layer and having a lower magnitude of resistivity on a plane of the transparent electrode than the contact metal, and a bonding pad formed on the current diffusion layer; wherein the transparent electrode contains a layer of an electroconductive oxide; and wherein the contact metal layer is formed of a platinum group metal.
2. A transparent electrode according to claim 1 , wherein the bonding pad has an area of 90% or more held in direct contact with the current diffusion layer.
3. A transparent electrode according to claim 1 , wherein the bonding pad has an area of direct contact with the p-type semiconductor layer that is 10% or less.
4. A transparent electrode according to claim 1 , wherein the bonding pad avoids direct contact with the p-type semiconductor layer.
5. A transparent electrode according to claim 1 , wherein the current diffusion layer has an uppermost layer covered with a metal layer formed of tin and/or indium.
6. A transparent electrode according to claim 1 , wherein the contact metal layer is formed of platinum.
7. A transparent electrode according to claim 1 , wherein the contact metal layer has a thickness in a range of 0.1 to 7.5 nm.
8. A transparent electrode according to claim 1 , wherein the contact metal layer has a thickness of 5 nm or less.
9. A transparent electrode according to claim 1 , wherein the contact metal layer has a thickness in a range of 0.5 to 2.5 nm.
10. A transparent electrode according to claim 1 , wherein the current diffusion layer is formed of a metal selected from the group consisting of gold, silver and copper or an alloy containing at least one of these.
11. A transparent electrode according to claim 1 , wherein the current diffusion layer is formed of gold.
12. A transparent electrode according to claim 1 , wherein the current diffusion layer has a thickness in a range of 1 to 20 nm.
13. A transparent electrode according to claim 1 , wherein the current diffusion layer has a thickness of 10 nm or less.
14. A transparent electrode according to claim 1 , wherein the current diffusion layer has a thickness in a range of 3 to 6 nm.
15. A transparent electrode according to claim 1 , wherein the bonding pad contains a first layer contacting the current diffusion layer, and the first layer is formed of at least one metal selected from the group consisting of Ti, Al, Au, and Cr or an alloy thereof.
16. A transparent electrode according to claim 15 , wherein the first layer of the bonding pad has a thickness in a range of 20 to 3000 nm.
17. A transparent electrode according to claim 15 , wherein the bonding pad contains a second layer formed on the first layer of the bonding pad, and the second layer is formed of at least one metal selected from Ti and Cr or an alloy thereof.
18. A transparent electrode according to claim 17 , wherein the second layer of the bonding pad has a thickness in a range of 20 to 3000 nm.
19. A transparent electrode according to claim 1 , wherein the bonding pad has an uppermost layer formed of Au.
20. A light-emitting device using the transparent electrode set forth in claim 1 .