Light-emitting device with distributed Bragg reflection structure
A light-emitting device includes a substrate having a first surface and a second surface opposite to the first surface; a light-emitting stack formed on the first surface; and a distributed Bragg reflection structure formed on the second surface, wherein the distributed Bragg reflection structure includes a first film stack and a second film stack; wherein the first film stack includes a plurality of first dielectric-layer pairs consecutively arranged, the second film stack includes a plurality of second dielectric-layer pairs consecutively arranged, each of the first dielectric-layer pairs and each of the second dielectric-layer pairs respectively includes a first dielectric layer having an optical thickness and a second dielectric layer having an optical thickness; wherein the second dielectric layer has a refractive index higher than that of the first dielectric layer; wherein in each of the first dielectric-layer pairs of the first film stack, the optical thickness of the first dielectric layer to the optical thickness of the second dielectric layer have a first ratio, and in each of the second dielectric-layer pairs of the second film stack, the optical thickness of the first dielectric layer to the optical thickness of the second dielectric layer have a second ratio; wherein the first ratio is greater than the second ratio; and wherein the first film stack is farther from the second surface of the substrate than the second film stack.
1. A light-emitting device, comprising:
a substrate comprising a first surface and a second surface opposite to the first surface;
a light-emitting stack formed on the first surface of the substrate;
a distributed Bragg reflection structure formed on the second surface of the substrate, wherein the distributed Bragg reflection structure comprises a first film stack and a second film stack;
wherein the first film stack comprises a plurality of first dielectric-layer pairs consecutively arranged, the second film stack comprises a plurality of second dielectric-layer pairs consecutively arranged, each of the first dielectric-layer pairs and each of the second dielectric-layer pairs respectively comprises a first dielectric layer having an optical thickness and a second dielectric layer having an optical thickness;
wherein the second dielectric layer has a refractive index higher than that of the first dielectric layer;
wherein in each of the first dielectric-layer pairs of the first film stack, the optical thickness of the first dielectric layer to the optical thickness of the second dielectric layer has a first ratio, and in each of the second dielectric-layer pairs of the second film stack, the optical thickness of the first dielectric layer to the optical thickness of the second dielectric layer has a second ratio;
wherein the first ratio is greater than the second ratio; and
wherein the first film stack is farther from the second surface of the substrate than the second film stack; and
a third film stack comprising a plurality of third dielectric-layer pairs;
wherein the third film stack is between the first film stack and the second film stack, or nearer to or farther from the second surface of the substrate than the first film stack and the second film stack.
2. The light-emitting device according to claim 1 , wherein the first ratio is greater than or equal to 1.5 and less than or equal to 1.8.
3. The light-emitting device according to claim 1 , wherein the second ratio is greater than or equal to 0.8, and less than or equal to 1.2.
4. The light-emitting device according to claim 1 , further comprising an interface layer between the substrate and the distributed Bragg reflection structure.
5. The light-emitting device according to claim 4 , wherein the interface layer has an optical thickness which is greater than or equal to a length of a central wavelength of a visible light band.
6. The light-emitting device according to claim 5 , wherein the visible light band ranges between 400 nm and 700 nm, and the central wavelength is 550 nm.
7. The light-emitting device according to claim 1 wherein the third dielectric-layer pairs comprise a third dielectric layer having an optical thickness and a fourth dielectric layer having an optical thickness;
wherein in each of the third dielectric-layer pairs of the third film stack, the optical thickness of the third dielectric layer to the optical thickness of the second dielectric layer has a third ratio; and
wherein the third ratio is greater than or equal to 0.8, and less than or equal to 1.2.
8. The light-emitting device according to claim 1 , further comprising an anti-interference layer, wherein the distributed Bragg reflection structure is located between the substrate and the anti-interference layer.
9. The light-emitting device according to claim 8 , wherein the anti-interference layer has an optical thickness which is ⅛ times a central wavelength of a visible light band.
10. The light-emitting device according to claim 9 , wherein the visible light band ranges between 400 nm and 700 nm, and the central wavelength is 550 nm.
11. The light-emitting device according to claim 1 , wherein the first dielectric-layer pairs comprise a half pair of the first dielectric-layer pairs and/or the second dielectric-layer pairs comprises a half pair of the second dielectric-layer pairs.
12. The light-emitting device according to claim 1 , wherein the first dielectric layers of the first dielectric-layer pairs and the first dielectric layers of the second dielectric-layer pairs comprise the same materials.