Light-emitting element with multiple light-emitting stacked layers

1. A light-emitting element, comprising:

a first active layer, generating a first light comprising a first dominant wavelength, wherein the first active layer comprises a first quantum well comprising a first quantum-well band gap and a second quantum well comprising a second quantum-well band gap, and the first quantum well and the second quantum well are alternately stacked to form the first active layer, wherein a difference between the first quantum-well band gap and the second quantum-well band gap is between 0.06 eV and 0.1 eV, and each of the first quantum-well and the second quantum-well is devoid of a barrier; and

a second active layer on the first active layer, generating a second light comprising a second dominant wavelength;

wherein a difference between the first dominant wavelength and the second dominant wavelength is 150 nm to 220 nm.

2. The light-emitting element of claim 1 , further comprising a substrate under the first active layer,

wherein the first dominant wavelength is larger than the second dominant wavelength.

3. The light-emitting element of claim 1 , wherein a wavelength of the first dominant wavelength is between 780 nm and 900 nm.

4. The light-emitting element of claim 1 , wherein a wavelength of the second dominant wavelength is between 560 nm and 750 nm.

5. A light-emitting element, comprising:

a first active layer, comprising a first band gap, wherein the first active layer comprises a first quantum well comprising a first quantum-well band gap and a second quantum well comprising a second quantum-well band gap, and the first quantum well and the second quantum well are alternately stacked to form the first active layer, wherein a difference between the first quantum-well band gap and the second quantum-well band gap is between 0.06 eV and 0.1 eV; and

a second active layer on the first active layer, comprising a second band gap;

wherein a difference between the first band gap and the second band gap is between 0.3 eV and 0.5 eV.

6. The light-emitting element of claim 5 , further comprising a substrate under the first active layer,

wherein the first band gap is larger than the second band gap.

7. The light-emitting element of claim 5 , wherein the second active layer comprises a third quantum well and a forth quantum well alternately stacked to form the second active layer, and each of the third quantum-well and the fourth'd of a barrier.

8. The light-emitting element of claim 7 , wherein the third quantum well comprises a third quantum-well band gap, a forth quantum well comprises a forth quantum-well band gap, and a difference between the third quantum-well band gap and the forth quantum-well band gap is between 0.06 eV and 0.1 eV.

9. The light-emitting element of claim 5 , further comprising:

a substrate under the first active layer;

a first semiconductor layer between the first active layer and the substrate;

a second semiconductor layer between the first active layer and the second active layer;

a third semiconductor layer between the second semiconductor layer and the second active layer; and

a forth semiconductor layer on the second active layer.

10. The light-emitting element of claim 9 , wherein a material of the substrate is selected from a group consisting of GaAs, SiC, and sapphire.

11. The light-emitting element of claim 9 , wherein materials of the first semiconductor layer, the second semiconductor layer, the third semiconductor layer, and/or the forth semiconductor layer comprise more than one element selected from a group consisting of Ga, Al, In, As, P, N, Zn, Cd, and Se.

12. The light-emitting element of claim 9 , further comprising a tunneling layer or a bonding layer between the second semiconductor layer and the third semiconductor layer.

13. The light-emitting element of claim 12 , wherein a material of the tunneling layer comprises more than one element selected from a group consisting of Ga, Al, In, As, P, N, Zn, Cd, and Se.

14. The light-emitting element of claim 12 , wherein a material of the bonding layer is selected from a group consisting of ITO, InO, SnO, CTO, ATO, ZnO, MgO, AlGaAs, GaN, GaP, AZO, ZTO, GZO, IZO, and Ta2O5.

15. The light-emitting element of claim 5 , wherein a material of the first active layer and/or the second active layer comprise more than one element selected from a group consisting of Ga, Al, In, As, P, N, Zn, Cd, and Se.

16. A light-emitting element, comprising:

a first active layer, generating an invisible light, wherein the first active layer comprises a first quantum well comprising a first quantum-well band gap and a second quantum well comprising a second quantum-well band gap, and the first quantum well and the second quantum well are alternately stacked to form the first active layer, wherein a difference between the first quantum-well band gap and the second quantum-well band gap is between 0.06 eV and 0.1 eV, and each of the first quantum-well and the second quantum-well is devoid of a barrier; and

a second active layer on the first active layer, generating a visible light.

17. The light-emitting element of claim 16 , further comprising a substrate under the first active layer,

wherein the first active layer comprises a first band gap, the second active layer comprises a second band gap, and the first band gap is larger than the second band gap.

18. The light-emitting element of claim 16 , wherein a difference between the wavelength of the visible light and the invisible light is between 150 nm and 220 nm.