Semiconductor LED flip-chip with dielectric coating on the mesa
View Patent ↗A dielectric layer is formed on the mesa wall of a flip-chip LED. The dielectric layer is selected to maximize reflection of light incident at angles ranging from 10 degrees towards the substrate to 30 degrees away from the substrate. In some embodiments, the LED is a III-nitride device with a p-contact containing silver, the dielectric layer adjacent to the mesa wall is a material with a low refractive index compared to GaN, such as Al 2 O 3 .
1. A light emitting device comprising:
an n-type layer;
an active region overlying the n-type layer;
a p-type layer overlying the active region;
an n-contact connected to the n-type layer;
a p-contact comprising silver and connected to the p-type layer, wherein the n-contact and the p-contact are formed on the same side of the device and the n-contact is electrically isolated from the p-contact by a mesa wall; and
a dielectric layer formed on the mesa wall.
2. The light emitting device of claim 1 , wherein the n-type layer, the active region, and the p-type layer are III-nitride materials.
3. The light emitting device of claim 1 wherein an angle between the mesa wall and the substrate is about 35 degrees to 55 degrees.
4. The light emitting device of claim 1 wherein the dielectric layer is reflective of light emitted by the active region.
5. The light emitting device of claim 1 further comprising a metal layer overlying the dielectric layer, wherein the metal layer is connected to one of the p-contact and the n-contact.
6. The light emitting device of claim 1 wherein the dielectric layer has a refractive index less than a refractive index of any of the n-type layer, the p-type layer, and the active region.
7. The light emitting device of claim 1 wherein the dielectric layer has a refractive index less than about 1.8.
8. The light emitting device of claim 1 wherein the dielectric layer is selected from a group consisting of oxides of silicon, nitrides of silicon, oxy-nitrides of silicon, aluminum oxides, fluorides of lithium, fluorides of calcium, and fluorides of magnesium.
9. The light emitting device of claim 1 wherein the dielectric layer has a refractive index less than 2.1.
10. The light emitting device of claim 1 wherein the dielectric layer is selected from a group consisting of tin oxide, aluminum nitride, antimony oxide, yttrium oxide, silicon monoxide, cerium oxide, and hafnium oxide.
11. The light emitting device of claim 1 wherein a thickness of the dielectric layer is about equal to
n
λ
4
1
2
wherein n is an odd integer and λ is a wavelength of light in the dielectric layer.
12. The light emitting device of claim 1 wherein a thickness of the dielectric layer is about equal to
n
λ
sin
θ
4
wherein n is an odd integer, λ is a wavelength of light in the dielectric layer, and θ is a measure of an angle between the mesa wall and the substrate.
13. The light emitting device of claim 1 wherein a composition and a thickness of the dielectric layer are selected to maximize reflection of light incident on the mesa wall at angles of propagation ranging from 10 degrees towards the substrate to 30 degrees away from the substrate.
14. The light emitting device of claim 1 wherein the dielectric layer comprises an aluminum oxide.