Light emitting diode
A light emitting diode with a front surface adapted to emit light and a rear surface is provided with a reflective coating on the rear surface, the reflective coating being primarily silver and containing either 0.4% bismuth or a combination of 0.5% tin, 0.2% copper, and 0.2% samarium.
1. A light emitting diode comprising a front surface adapted to emit light and a rear surface; a reflective layer on the rear surface of the light emitting diode adapted to reflect light toward the light emitting diode front surface, the reflective layer comprising:
a silver tin copper samarium composition having 0.5% tin, 0.2% copper, and 0.2% samarium and the balance silver.
2. The light emitting diode of claim 1 wherein the light emitting diode is on a sapphire substrate and the reflective layer is on the sapphire substrate.
3. The light emitting diode of claim 1 wherein the reflective layer has improved resistance to environmental degradation as compared to a reflective layer of pure silver, and thereby has improved adhesion characteristics, improved anti-corrosion characteristics, and improved stability.
4. The light emitting diode of claim 3 having an extended life time at rated light output as compared to a light emitting diode having a reflective layer of pure silver.
5. The light emitting diode of claim 1 , wherein the reflective layer is a sputtered reflective layer.
6. A silver alloy for application as a reflective coating to a light emitting diode, the alloy comprising 0.5% tin, 0.2% copper, and 0.2% samarium and the balance silver.
7. A method of creating an improved light emitting diode comprising the steps of:
providing a light emitting diode having a front surface adapted to emit light and a rear surface; and
coating the rear surface of the light emitting diode with a reflective coating comprising:
a silver tin copper samarium composition having 0.5% tin, 0.2% copper, and 0.2% samarium and the balance silver.
8. The method of claim 7 wherein the coating is applied to the light emitting diode by sputtering.
9. The method of claim 7 wherein the coating is applied to the light emitting diode while the light emitting diode is part of a wafer of several light emitting diodes.
10. The method of claim 9 , wherein the coating is applied to the light emitting diode by sputtering.
11. The method of claim 10 , further comprising separating the light emitting diode from the wafer.
12. A wafer comprising a front surface, a back surface, and a plurality of dies formed thereon including light emitting diodes, wherein the back surface is coated with a reflective layer, the reflective layer comprising:
a silver tin copper samarium composition having 0.5% tin, 0.2% copper, and 0.2% samarium and the balance silver.
13. The wafer of claim 12 , further comprising a sapphire substrate, wherein the reflective layer is on the sapphire substrate.
14. The wafer of claim 13 , wherein the reflective layer has improved resistance to environmental degradation as compared to a reflective layer of pure silver, and thereby has improved adhesion characteristics, improved anti-corrosion characteristics, and improved stability.
15. The wafer of claim 12 , wherein the reflective layer is a sputtered reflective layer.