Gallium nitride light-emitting device with ultra-high reverse breakdown voltage

1. A gallium nitride (GaN)-based semiconductor light-emitting device (LED), comprising:

an n-type GaN-based semiconductor layer (n-type layer);

an active layer; and

a p-type GaN-based semiconductor layer (p-type layer);

wherein the n-type layer is epitaxially grown by using ammonia gas (NH 3 ) as the nitrogen source prior to growing the active layer and the p-type layer;

wherein a flow rate ratio between group V and group III elements, or a V/III ratio, during the epitaxial growth of the n-type layer is gradually reduced from an initial value to a final value; and

wherein the n-type layer includes a sublayer grown after the V/III ratio is reduced to the final value, the sublayer thus having a substantially lower Ga/N ratio than the rest of the n-type layer; wherein the sublayer is in contact with the active layer, and wherein the sublayer has a thickness of less than 1000 angstroms.

2. The GaN-based semiconductor LED of claim 1 ,

wherein the GaN-based LED exhibits a reverse breakdown voltage equal to or greater than 60 volts.

3. The GaN-based semiconductor LED of claim 1 ,

wherein the initial V/III ratio is approximately between 1000 and 10000; and

wherein the final V/III ratio is approximately between 150 and 500.

4. The GaN-based semiconductor LED of claim 3 ,

wherein the initial V/III ratio is approximately between 2000 and 5000.

5. The GaN-based semiconductor LED of claim 3 ,

wherein the final V/III ratio is approximately between 200 and 300.

6. The GaN-based semiconductor LED of claim 1 ,

wherein the active layer is sufficiently close to the location in the n-type layer where the final V/III ratio is reached.

7. The GaN-based semiconductor LED of claim 6 ,

wherein the active layer is within 1000 angstroms to the location in the n-type layer where the final V/III ratio is reached.

8. The GaN-based semiconductor LED of claim 1 ,

wherein the V/III ratio reduction process starts shortly after the n-type layer epitaxial growth begins.

9. The GaN-based semiconductor LED of claim 1 ,

wherein the V/III ratio reduction process is substantially linear with a substantially constant reduction rate.

10. The GaN-based semiconductor LED of claim 1 ,

wherein the duration of the reduction of the V/III ratio from the initial V/III ratio to the final V/III ratio is sufficiently long.

11. The GaN-based semiconductor LED of claim 1 ,

wherein the reverse breakdown voltage of the GaN-based LED is equal to or greater than 110 volts.

12. The GaN-based semiconductor LED of claim 1 ,

wherein the turn-on voltage of the GaN-based LED is equal to or less than 3 volts.

13. The GaN-based semiconductor LED of claim 1 ,

wherein the active layer is an InGaN/GaN multiple-quantum-well (MQW) layer.

14. A method for fabricating a gallium nitride (GaN)-based semiconductor light-emitting device (LED), comprising:

epitaxially growing on a growth substrate an n-type GaN-based semiconductor layer (n-type layer) using ammonia gas (NH 3 ) as the nitrogen source, wherein while epitaxially growing the n-type layer, gradually reducing a flow rate ratio between group V and group III elements, or a V/III ratio, from an initial value to a final value, and wherein the gradual reduction of the flow rate has a duration that is equal to or greater than a total time for epitaxially growing the n-type layer; and

epitaxially growing an active layer and a p-type GaN-based semiconductor layer (p-type layer) on the n-type layer, wherein the active layer is adjacent to an n-type GaN sublayer that is grown after the V/III ratio is reduced to the final value;

wherein the n-type layer, the active layer, and the p-type layer form the structure of the GaN-based LED.

15. The method of claim 14 ,

wherein the GaN-based LED exhibits a reverse breakdown voltage equal to or greater than 60 volts.

16. The method of claim 14 ,

wherein the initial V/III ratio is approximately between 1000 and 10000; and

wherein the final V/III ratio is approximately between 150 and 500.

17. The method of claim 16 ,

wherein the initial V/III ratio is approximately between 2000 and 5000.

18. The method of claim 16 ,

wherein the final V/III ratio is approximately between 200 and 300.

19. The method of claim 14 , wherein the active layer is sufficiently close to the location in the n-type layer where the final V/III ratio is reached.

20. The method of claim 19 , wherein the active layer is within 1000 angstroms to the location in the n-type layer where the final V/III ratio is reached.

21. The method of claim 14 , wherein the method further comprises starting the V/III ratio reduction process shortly after the n-type layer epitaxial growth begins.

22. The method of claim 14 , wherein gradually reducing the V/III ratio involves reducing the V/III ratio substantially linearly from the initial V/III ratio to the final V/III ratio.

23. The method of claim 14 , wherein the duration of gradually reducing the V/III ratio from the initial V/III ratio to the final V/III ratio is sufficiently long.

24. The method of claim 14 , wherein the reverse breakdown voltage of the GaN-based LED is equal to or greater than 110 volts.

25. The method of claim 14 , wherein the turn-on voltage of the GaN-based LED is equal to or less than 3 volts.

26. The method of claim 14 , wherein the active layer is an InGaN/GaN multiple-quantum-well (MQW) layer.

27. A system for fabricating a gallium nitride (GaN)-based semiconductor light-emitting device (LED), comprising:

a deposition mechanism configured to epitaxially grow on a growth substrate an n-type GaN-based semiconductor layer (n-type layer) while using ammonia gas (NH 3 ) as the nitrogen source,

wherein the deposition mechanism is configured to gradually reduce a flow rate ratio between group V and group III elements, or a VIII ratio, from an initial value to a final value, wherein the gradual reduction of the flow rate has a duration that is equal to or greater than a total time for epitaxially growing the n-type layer;

wherein the deposition mechanism is configured to epitaxially grow an active layer and a p-type GaN-based semiconductor layer (p-type layer) on the n-type layer;

wherein the n-type layer, the active layer, and the p-type layer form the structure of the GaN-based LED, wherein the active layer is adjacent to an n-type GaN sublayer that is grown after the V/III ratio is reduced to the final value; and

wherein the GaN-based LED exhibits a reverse breakdown voltage equal to or greater than 60 volts.