LED with scattering features in substrate
View Patent ↗In one embodiment, the transparent growth substrate ( 38 ) of an LED die is formed to have light scattering areas ( 40 A-C), such as voids formed by a laser. In another embodiment, the growth substrate is removed and replaced by another substrate that is formed with light scattering areas. In one embodiment, the light scattering areas are formed over the light absorbing areas of the LED die, to reduce the amount of incident light on those absorbing areas, and over the sides ( 42 A, 42 B) of the substrate to reduce light guiding. Another embodiment comprises a replacement substrate may be formed to include reflective particles in selected areas where there are no corresponding light generating areas in the LED semiconductor layers such as—type metal contacts ( 28 ). This prevents reabsorption into absorbing regions of the semiconductor layer thereby enhancing external efficiency of the device. A 3D structure may be formed by stacking substrate layers containing the reflective areas. The substrate may be a transparent substrate or a phosphor tile ( 20 ) that is affixed to the top of the LED.
1. A light emitting device comprising:
light emitting diode (LED) semiconductor layers generating light, the LED semiconductor layers having a light emitting surface;
a substrate overlying the light emitting surface and affixed to the LED semiconductor layers; and
one or more light scattering areas formed within the substrate,
wherein the LED semiconductor layers include areas that generate light and areas that do not generate light, wherein the one or more light scattering areas are located over at least one of the LED semiconductor layer areas that do not generate light, and
wherein the one or more light scattering areas are not formed over the LED semiconductor layers areas that generate light.
2. The device of claim 1 wherein the one or more light scattering areas comprise reflective particles within the substrate in only selected areas of the substrate and not throughout the substrate.
3. The device of claim 1 wherein the one or more light scattering areas comprise reflective voids formed within the substrate.
4. The device of claim 1 wherein the substrate is a growth substrate on which the LED semiconductor layers have been epitaxially grown.
5. The device of claim 1 wherein the substrate is affixed to the light emitting surface of the LED semiconductor layers with an adhesive.
6. The device of claim 1 wherein the one or more light scattering areas comprise reflective metal particles.
7. The device of claim 1 wherein at least one of the one or more light scattering areas is formed overlying a light absorbing area within or underlying the LED semiconductor layers.
8. The device of claim 1 further comprising metal contacts for the LED semiconductor layers, wherein the LED semiconductor layers comprise an N-type layer and a P-type layer, and wherein at least one of the one or more light scattering areas is formed over a metal contact for the N-type layer.
9. The device of claim 1 wherein the one or more light scattering areas are formed along sidewalls of the substrate.
10. The device of claim 1 wherein the substrate comprises a wavelength converting material.
11. The device of claim 1 further comprising a phosphor layer overlying the substrate, the one or more light scattering areas being positioned to scatter light from the phosphor layer that has been emitted toward the LED semiconductor layers, such that some of the light is reflected back toward the phosphor layer.
12. The device of claim 1 wherein at least one of the one or more light scattering areas is located proximate a bottom surface of the substrate proximate to the LED semiconductor layers.
13. The device of claim 1 wherein at least one of the one or more light scattering areas is located proximate to a top surface of the substrate away from the LED semiconductor layers.
14. The device of claim 1 wherein the substrate is transparent except for the one or more light scattering areas.