Light emitting unit array and projection system
A light emitting unit array including a plurality of micro-light emitting diodes (μ-LEDs) is provided. The micro-light emitting diodes are arranged in an array on a substrate, and each of the micro-light emitting diodes includes a reflection layer, a light emitting structure, and a light collimation structure. The light emitting structure is disposed on the reflection layer, and includes a first type doped semiconductor layer, an active layer, and a second type doped semiconductor layer that are stacked sequentially. At least a portion of the first type doped semiconductor layer, the active layer, and the second type doped semiconductor layer are sandwiched between the reflection layer and the light collimation structure.
1. A light emitting unit array, comprising:
a plurality of micro-light emitting diodes arranged in an array on a substrate, each of the micro-light emitting diodes comprising:
a reflection layer;
a light emitting structure disposed on the reflection layer, and the light emitting structure comprising a first type doped semiconductor layer, an active layer, and a second type doped semiconductor layer that are stacked sequentially; and
a light collimation structure, wherein at least a portion of the first type doped semiconductor layer, the active layer, and the second type doped semiconductor layer are sandwiched between the reflection layer and the light collimation structure, and the light collimation structure of each of the micro-light emitting diodes is buried in the first type doped semiconductor layer.
2. The light emitting unit array as claimed in claim 1 , wherein the light collimation structure of each of the micro-light emitting diodes comprises a distributed Bragg reflector or an omni-directional reflector.
3. The light emitting unit array as claimed in claim 2 , wherein a thickness of the light emitting structure of each of the micro-light emitting diodes located between the light collimation structure and the reflection layer is L, the wavelength of the light emitted from the active layer is λ, and L and λ complies with L=n/2λ while n is an integer and ranges between 3 and 20.
4. The light emitting unit array as claimed in claim 1 , wherein the light collimation structures of the micro-light emitting diodes are connected with one another to form a continuous distributed Bragg reflector layer.
5. The light emitting unit array as claimed in claim 1 , wherein the light collimation structure of each of the micro-light emitting diodes has a plurality of concaves.
6. The light emitting unit array as claimed in claim 5 , further comprising a plurality of distributed Bragg reflectors, wherein each of the distributed Bragg reflectors fills one of the concaves.
7. The light emitting unit array as claimed in claim 5 , wherein the concaves of the light collimation structure are arranged periodically to form a first photonic crystal structure layer.
8. The light emitting unit array as claimed in claim 7 , wherein the concaves of the first photonic crystal structure layer are filled with dielectric material.
9. The light emitting unit array as claimed in claim 7 , wherein each of the micro-light emitting diodes further comprises a second photonic crystal structure layer disposed between the light emitting structure and the reflection layer.
10. The light emitting unit array as claimed in claim 9 , wherein the second photonic crystal structure layer has a plurality of concaves filled with reflective material and the reflective material is the same as the material of the reflection layer.
11. A projection system, comprising:
a display unit array comprising a plurality of micro-light emitting diodes arranged in an array on a substrate, and each of the micro-light emitting diodes comprising:
a reflection layer;
a light emitting structure disposed on the reflection layer, and the light emitting structure comprising a first type doped semiconductor layer, an active layer, and a second type doped semiconductor layer that are stacked sequentially; and
a light collimation structure, wherein at least a portion of the first type doped semiconductor layer, the active layer, and the second type doped semiconductor layer are sandwiched between the reflection layer and the light collimation structure, and the light collimation structure of each of the micro-light emitting diodes is buried in the first type doped semiconductor layer; and
a projection lens set located at the light path of the displaying light of the display unit array.
12. The projection system as claimed in claim 11 , wherein the light collimation structure of each of the micro-light emitting diodes comprises a distributed Bragg reflector or an omni-directional reflector.
13. The projection system as claimed in claim 12 , wherein a thickness of the light emitting structure of each of the micro-light emitting diodes located between the light collimation structure and the reflection layer is L, the wavelength of the light emitted from the active layer is λ, and L and λ complies with L=n/2λ while n is an integer and 3<n<20.
14. The projection system as claimed in claim 11 , wherein the light collimation structure of each of the micro-light emitting diodes has a plurality of concaves.
15. The projection system as claimed in claim 14 , further comprising a plurality of distributed Bragg reflectors, wherein each of the distributed Bragg reflectors fills one of the concaves.
16. The projection system as claimed in claim 14 , wherein the concaves of the light collimation structure are arranged periodically to form a first photonic crystal structure layer.
17. The projection system as claimed in claim 16 , wherein the concaves of the first photonic crystal structure layer are filled with dielectric material.
18. The projection system as claimed in claim 16 , wherein each of the micro-light emitting diodes further comprises a second photonic crystal structure layer disposed between the light emitting structure and the reflection layer.
19. The projection system as claimed in claim 18 , wherein the second photonic crystal structure layer has a plurality of concaves filled with reflective material and the reflective material is the same as the material of the reflection layer.
20. The projection system as claimed in claim 11 , further comprising a micro-lens array formed by a plurality of micro-lens and each of the micro-lens being disposed on one of the micro-light emitting diodes.