Method and structure for LED with nano-patterned substrate

1. A method comprising:

forming a nano-mask layer on a first substrate, wherein the nano-mask layer has a randomly arranged grain pattern;

growing a first epitaxy semiconductor layer in the first substrate, forming a nano-composite layer;

growing a number of epitaxy semiconductor layers over the nano-composite layer;

bonding a second substrate to the epitaxy semiconductor layers from a first side of the epitaxy semiconductor layers;

applying a radiation energy to the nano-composite layer; and

separating the first substrate from the epitaxy semiconductor layers from a second side of the epitaxy semiconductor layers.

2. The method of claim 1 , wherein the forming of the nano-mask layer includes:

forming a material layer on the first substrate; and

performing a thermal treatment to the material layer.

3. The method of claim 1 , wherein the forming of the nano-mask layer includes:

forming a thin metal film on the first substrate; and

annealing the thin metal film such that the thin metal film is liquidized and forms nano-sized grains under surface tension.

4. The method of claim 3 , wherein the thin metal film includes at least one of nickel and silver.

5. The method of claim 1 , wherein the forming of the nano-mask layer includes:

coating a polymeric solution containing nano-sized particles on the first substrate; and

curing the polymeric solution to form the nano-mask layer having the randomly arranged grains on the first substrate.

6. The method of claim 5 , wherein the nano-mask layer includes one of polyimide and poly(methyl methacrylate).

7. The method of claim 1 , wherein the forming of the nano-mask layer includes:

coating a liquid precursor containing nano-sized particles on the first substrate; and

performing a thermal treatment to remove solvent from the liquid precursor and form the nano-mask layer of a dielectric material on the first substrate.

8. The method of claim 7 , wherein the dielectric material includes at least one of aluminum oxide and aluminum nitride.

9. The method of claim 1 , wherein the first substrate includes sapphire and the second substrate includes one of a silicon wafer and a metal plate.

10. The method of claim 1 , further comprising forming a dielectric material layer on the first substrate and the forming of the nano-mask layer includes forming the nano-mask layer on the dielectric material layer.

11. The method of claim 10 , further comprising etching the dielectric material layer using the nano-mask layer as an etch mask prior to the growing of a first epitaxy semiconductor layer, thereby forming openings in the dielectric material layer, wherein the growing of the first epitaxy semiconductor layer includes growing the first epitaxy semiconductor layer within the openings of the dielectric material layer.

12. The method of claim 11 , wherein the etching of the dielectric material layer includes implementing a reactive ion etch (RIE) process.

13. The method of claim 1 , wherein:

the first epitaxy semiconductor layer includes an un-doped gallium nitride (GaN) layer; and

the number of epitaxy semiconductor layers include a n-type doped gallium nitride (n-GaN) layer and a p-type doped gallium nitride (p-GaN) layer.

14. The method of claim 13 , wherein the number of epitaxy semiconductor layers further include a multiple quantum well (MQW) structure disposed between the n-GaN layer and the p-GaN layer.

15. The method of claim 14 , wherein the separating of the first substrate from the epitaxy semiconductor layers includes applying a mechanical force to break the nano-composite layer from the first substrate.

16. The method of claim 14 , further comprising, after the separating the first substrate from the epitaxy semiconductor layers, performing an etching process to the epitaxy semiconductor layers, generating a rough surface of the epitaxy semiconductor layers.

17. A method comprising:

forming a dielectric material layer on a sapphire substrate;

forming a nano-mask layer on the dielectric material layer, wherein the nano-mask layer includes nano-sized grains randomly distributed on the dielectric material layer;

performing a first etching process to remove the dielectric material layer uncovered by the nano-mask layer, forming nano-rods each including a dielectric feature from the dielectric material layer and one of the nano-sized grains overlying the dielectric feature;

growing a first epitaxy semiconductor layer on the sapphire substrate within gaps of the nano-rods, forming a nano-composite layer having the first epitaxy semiconductor layer and the nano-rods embedded in the first epitaxy semiconductor layer;

growing epitaxy semiconductor layers on the nano-composite layer;

bonding another substrate to the epitaxy semiconductor layers;

applying a radiation energy to the nano-composite layer;

applying a mechanical force to the nano-rods to separate the sapphire substrate from the epitaxy semiconductor layers; and

performing a second etching process to the epitaxy semiconductor layers, resulting in a rough surface of the epitaxy semiconductor layers.

18. The method of claim 17 , wherein the applying of the radiation energy includes applying a laser power to the nano-composite layer.

19. The method of claim 17 , wherein the forming of the nano-mask layer includes:

forming a material layer on the dielectric material layer; and

performing a thermal treatment to the material layer to form the nano-mask layer.

20. The method of claim 17 , wherein the nano-sized grains have:

diameters distributed between about 100 nm and about 600 nm; and

a grain density ranging from about 10 7 grains/cm 2 to about 10 9 grains/cm 2 .