Low profile side emitting LED with window layer and phosphor layer
View Patent ↗Low profile, side-emitting LEDs are described that generate white light, where all light is emitted within a relatively narrow angle generally parallel to the surface of the light-generating active layer. The LEDs enable the creation of very thin backlights for backlighting an LCD. In one embodiment, the LED emits blue light and is a flip chip with the n and p electrodes on the same side of the LED. Separately from the LED, a transparent wafer has deposited on it a red and green phosphor layer. The phosphor color temperature emission is tested, and the color temperatures vs. positions along the wafer are mapped. A reflector is formed over the transparent wafer. The transparent wafer is singulated, and the phosphor/window dice are matched with the blue LEDs to achieve a target white light color temperature. The phosphor/window is then affixed to the LED.
1. A side-emitting light emitting device comprising:
a light emitting diode (LED) die comprising:
a first semiconductor layer of a first type;
a second semiconductor layer of a second type;
and active layer between the first semiconductor layer and the second semiconductor layer, the active layer having a major surface;
a first electrode in contact with the first semiconductor layer; and
a second electrode in contact with the second semiconductor layer, the first electrode and the second electrode being on a first side of the LED for being directly connected to electrodes on a submount, the LED being a flip chip;
the light emitting structure further comprising:
a window layer affixed to the LED die overlying the major surface of the active layer;
at least one phosphor layer coating a surface of the window layer for wavelength conversion of light emitted by the LED die; and
a reflector overlying a surface of the window layer, with the window layer and the at least one phosphor layer between the reflector and LED die, such that light emitted by the major surface of the active layer energizes the at least one phosphor layer, and the reflector substantially blocks light exiting the light emitting device normal to the major surface of the active layer such that a majority of light is emitted from sides of the light emitting device.
2. The device of claim 1 wherein the at least one phosphor layer and reflector are located on opposite surfaces of the window layer.
3. The device of claim 1 wherein the reflector is provided directly over the at least one phosphor layer.
4. The device of claim 1 wherein the window layer contains embedded light scattering features.
5. The device of claim 1 wherein the at least one phosphor layer comprises a single layer of mixed red and green phosphors.
6. The device of claim 1 wherein the at least one phosphor layer comprises a first layer of red phosphor and a second layer of green phosphor.
7. The device of claim 1 wherein the at least one phosphor layer comprises red, green, and blue phosphors.
8. The device of claim 1 wherein the LED die emits blue light.
9. The device of claim 1 wherein the LED die emits UV light.
10. The device of claim 1 wherein the window layer has a thickness greater than 100 microns, and the at least one phosphor layer has a thickness less than 50 microns.
11. The device of claim 1 wherein the at least one phosphor layer comprises at least two color phosphors in a transparent binder.
12. The device of claim 1 wherein the window layer has edges that extend over edges of the LED die.
13. The device of claim 1 wherein the window layer has scattering features in a surface adjacent the reflector.
14. The device of claim 1 wherein the LED die active layer is rectangular, and the window layer is non-rectangular and has edges that extend over edges of the LED die.
15. The device of claim 1 wherein the window layer has a concave surface adjacent the reflector.
16. The device of claim 1 further comprising a dichroic mirror between the LED die and the window layer, the dichroic mirror allowing light emitted from the LED die to pass and reflecting light emitted by the at least one phosphor layer.
17. The device of claim 1 wherein the at least one phosphor layer is within a tub formed in the window layer.
18. The device of claim 1 wherein sides of the window layer are roughened.
19. The device of claim 1 wherein the reflector is a diffusive reflector.
20. The device of claim 19 wherein the reflector is a substantially opaque layer comprising TiO 2 .