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.