Micro-LED device
A micro-LED, μLED, comprising: a substantially parabolic mesa structure; a light emitting source within the mesa structure; and a primary emission surface on a side of the device opposed to a top of the mesa structure; wherein the mesa structure has an aspect ratio, defined by (H 2 *H 2 )/Ac, of less than 0.5, and the μLED further comprises a reflective surface located in a region from the light emitting source to the primary emission surface, wherein the reflective surface has a roughness, Ra, less than 500 nm.
1. A micro-LED (μLED) comprising:
a substantially parabolic mesa structure;
a light emitting source within the mesa structure; and
a primary emission surface on a side of the μLED opposed to a top of the mesa structure;
wherein the mesa structure has an aspect ratio, defined by (H 2 *H 2 )/Ac, of less than 0.5, and the μLED further comprises a reflective surface located in a region from the light emitting source to the primary emission surface, wherein the reflective surface has a roughness Ra less than 500 nm, and wherein H 2 is a height of the light emitting source above a base of the mesa structure and Ac is a cross-sectional area of the mesa structure at the level of the light emitting source.
2. The μLED according to claim 1 , wherein the reflective surface is the primary emission surface.
3. The μLED according to claim 1 , wherein the roughness Ra is less than 300 nm.
4. The μLED according to claim 1 , wherein the reflective surface is an interface between a first material having a first refractive index and a second material having a second refractive index.
5. The μLED according to claim 4 , wherein the first material comprises an epilayer and the second material comprises a substrate upon which the μLED is fabricated.
6. The μLED according to claim 4 , wherein the μLED is formed from GaN on a sapphire substrate, and wherein the interface between two materials is the interface between the GaN and the sapphire substrate.
7. The μLED according to claim 1 , wherein the reflective surface has the roughness Ra less than 500 nm in a region greater than or equal to a cross sectional area of the base of the mesa structure, and aligned with a central axis of the mesa structure.
8. The μLED according to claim 1 , wherein the aspect ratio is less than 0.3.
9. The μLED according to claim 1 , wherein the mesa structure comprises a truncated top.
10. The μLED according to claim 1 , wherein the light emitting source is offset from a central axis of the mesa structure.
11. The μLED according to claim 10 , wherein the light emitting source is offset by a distance on one or both of perpendicular axes lying in a plane parallel to the primary emission surface.
12. The μLED according to claim 11 , wherein the offset distance in each of the perpendicular axes is in a range from 1 μm to 5 μm.
13. The μLED according to claim 11 , wherein the offset distance in each of the perpendicular axes is in a range from 10% to 50% of the total distance from the central axis to an edge of the mesa in each of the perpendicular axes.
14. The μLED according to claim 1 , wherein the light emitting source is configured to emit light anisotropically, such that the light is emitted from the light emitting source substantially in a direction perpendicular to the direction of emission of light from the μLED.
15. The μLED according to claim 14 , wherein the emission of light from the light emitting source is controlled using one or more of index guiding and dipole anisotropy.
16. The μLED according to claim 1 , further comprising an additive layer applied to the primary emission surface, wherein the additive layer attenuates light incident thereon at a given angle and/or at above a given wavelength.
17. The μLED according to claim 16 , wherein the additive layer is a multi-level dielectric filter.
18. The μLED according to claim 1 , wherein the source occupancy of the light emitting source within a light emitting layer of the mesa structure is in a range from 20% to 50%.