Light-emitting device having active layers stacked alternately

1. A light-emitting device, comprising:

a substrate;

a first conductivity type semiconductor layer on the substrate;

a light-emitting structure on the first conductivity type semiconductor layer, comprising:

a plurality of first active layers, each of first active layers having a quantum well structure and emitting a light with a first light-emitting wavelength; and

a plurality of second active layers, each of second active layers having a quantum well structure and emitting a light with a second light-emitting wavelength; and

a second conductivity type semiconductor layer on the light-emitting structure,

wherein the first active layers and the second active layers are stacked alternately, and wherein the first light-emitting wavelength is larger than the second light-emitting wavelength

wherein the first active layer is a single layer, and the second active layer comprises multiple layers, and

wherein the first light-emitting wavelength is the same for each of the first active layers and the second light-emitting wavelength is the same for each of the second active layers.

2. The light-emitting device according to claim 1 , wherein a number of the total layers of the first active layers and the second active layers is 23n, wherein n is an integer number greater than 0.

3. The light-emitting device according to claim 2 , wherein d layers of the second active layers are disposed between every two layers of the first active layers, wherein 4n≦d≦10n.

4. The light-emitting device according to claim 1 , wherein the substrate comprises gallium arsenic.

5. The light-emitting device according to claim 1 , wherein a material of the light-emitting structure can be AlGaInP series compound, AlGaInN series compound, or a combination of the two compounds.

6. A backlight module device, comprising:

a light source device having a light-emitting device made according to claim 1 ;

an optics device deposited on a light extraction pathway of the light source device; and

a power supply system to provide a predetermined power to the light source device.

7. An illumination device, comprising:

a light source device having a light-emitting device made according to claim 1 ;

a power supply system to provide a predetermined power of the light source device; and

a control element to control the current driven into the light source device.

8. The light-emitting device according to claim 1 , wherein the substrate comprises sapphire.

9. The light-emitting device according to claim 1 , wherein the substrate comprises silicon carbide.

10. The light-emitting device according to claim 1 , wherein the substrate comprises gallium nitride.

11. The light-emitting device according to claim 1 , wherein the substrate comprises aluminum nitride.

12. The light-emitting device according to claim 1 , wherein the substrate comprises silicon.