Nitride light-emitting diode

1. A nitride light-emitting diode, comprising:

a substrate;

an n-type nitride layer over the substrate;

a light-emitting layer over the n-type nitride layer;

a p-type nitride layer over the light-emitting layer;

a p+ nitride layer over the p-type nitride layer;

an AlInGaN gradient layer over the p+ nitride layer; and

an n+ nitride layer over the AlInGaN gradient layer;

wherein the p+ nitride layer, the AlInGaN gradient intermediate layer and the n+ nitride layer form a tunneling junction; and

wherein forbidden band width of the AlInGaN gradient layer is configured to be smaller than forbidden band widths of the p+ nitride layer and the n+ nitride layer to thereby increase tunneling probability.

2. The nitride light-emitting diode of claim 1 , wherein: polarization charges are generated at interface among the AlInGaN layer, the n+ nitride layer and the p+ nitride layer from lattice mismatch to thereby further increase the tunneling probability.

3. The nitride light-emitting diode of claim 1 , wherein: band gap width of the AlInGaN layer is larger than that of the light-emitting layer.

4. The nitride light-emitting diode of claim 1 , wherein: the AlInGaN gradient layer has gradient compositions configured to increase the tunneling probability.

5. The nitride light-emitting diode of claim 4 , wherein: in the AlInGaN gradient layer, the indium compositions initially increase and then decrease, forming an inverted V-type gradient structure, and the middle of the AlInGaN layer has a highest indium composition.

6. The nitride light-emitting diode of claim 4 , wherein: in the AlInGaN gradient layer, the indium compositions initially increase, then remain unchanged and finally decrease, forming a trapezoidal gradient structure.

7. The nitride light-emitting diode of claim 4 , wherein: in the AlInGaN gradient layer, the aluminum compositions initially decrease and then increase, forming a trapezoidal gradient structure.

8. The nitride light-emitting diode of claim 4 , wherein: in the AlInGaN gradient layer, the aluminum compositions initially decrease, then remain unchanged and finally increase, forming a trapezoidal gradient structure.

9. The nitride light-emitting diode of claim 1 , wherein: the AlInGaN gradient layer is 0.1-20 nm thick.

10. The nitride light-emitting diode of claim 1 , wherein: doping concentration and thickness of the p+ layer are 1E19-1E21 cm −3 and 0.1-20 nm, respectively.

11. The nitride light-emitting diode of claim 1 , wherein: doping concentration and thickness of the n+ layer are 1E19-1E21 cm −3 and 0.1-20 nm, respectively.

12. A method of forming a nitride light-emitting diode, wherein formed light-emitting diode comprises:

a substrate;

an n-type nitride layer over the substrate;

a light-emitting layer over the n-type nitride layer;

a p-type nitride layer over the light-emitting layer;

a p+ nitride layer over the p-type nitride layer;

an AlInGaN gradient layer over the p+ nitride layer; and

an n+ nitride layer over the AlInGaN gradient layer;

wherein the p+ nitride layer, the AlInGaN gradient intermediate layer and the n+ nitride layer form a tunneling junction;

wherein the AlInGaN gradient layer is grown to have a forbidden band width smaller than forbidden band widths of the p+ nitride layer and the n+ nitride layer to thereby increase tunneling probability;

the method comprising:

growing the p+ nitride layer;

growing the AlInGaN gradient layer over the p+ nitride layer; and

growing the n+ nitride layer over the AlInGaN gradient layer.

13. The method of claim 12 , wherein said growing the p+ nitride layer comprises Metal Organic Chemical Vapor Deposition (MOCVD) growth under:

an epitaxial wafer surface temperature of 800-1000° C.;

a growth reaction chamber pressure of 50-500 mbar;

Ga source and N source: TMGa and NH 3 ;

carrier gas: H 2 ; and

dopant: Cp2Mg;

wherein a growth thickness is 0.1-20 nm and a doping concentration is 1E19-1E21 cm −3 .

14. The method of claim 13 , wherein the temperature is about 930° C., and the pressure is about 200 mbar.

15. The method of claim 12 , wherein said growing the AlInGaN gradient layer over the p+ nitride layer is under:

a reaction chamber pressure of 50-500 mbar;

a substrate temperature of 650° C.-850° C.;

Ga, In, Al, and N sources: TMGa, TMIn, TMAl, and NH 3 ; and

carrier gas: H 2 .

16. The method of claim 15 , wherein the temperature is about 770° C., and the pressure is about 200 mbar.

17. The method of claim 12 , wherein said growing the n+ nitride layer over the AlInGaN gradient layer is under:

an epitaxial wafer surface temperature at 800-1,000° C.;

a growth reaction chamber pressure: 50-500 mbar;

Ga source and N source: TMGa and NH 3 ;

carrier gas: H 2 ,

dopant: SiH 4 ;

growth thickness: 0.1-20 nm; and

doping concentration: 1E19-1E21 cm −3 .

18. A light-emitting system comprising a plurality of nitride light-emitting diodes (LEDs), each LED comprising:

a substrate;

an n-type nitride layer over the substrate;

a light-emitting layer over the n-type nitride layer;

a p-type nitride layer over the light-emitting layer;

a p+ nitride layer over the p-type nitride layer;

an AlInGaN gradient layer over the p+ nitride layer; and

an n+ nitride layer over the AlInGaN gradient layer;

wherein the p+ nitride layer, the AlInGaN gradient intermediate layer and the n+ nitride layer form a tunneling junction; and

wherein forbidden band width of the AlInGaN gradient layer is configured to be smaller than forbidden band widths of the p+ nitride layer and the n+ nitride layer to thereby increase tunneling probability.

19. The light-emitting system of claim 18 , wherein: polarization charges are generated at interface among the AlInGaN layer, the n+ nitride layer and the p+ nitride layer from lattice mismatch to thereby further increase the tunneling probability.