Methods for producing composite GaN nanocolumns and light emitting structures made from the methods
A method for growing on a substrate strongly aligned uniform cross-section semiconductor composite nanocolumns is disclosed. The method includes: (a) forming faceted pyramidal pits on the substrate surface; (b) initiating nucleation on the facets of the pits; and; (c) promoting the growth of nuclei toward the center of the pits where they coalesce with twinning and grow afterwards together as composite nanocolumns. Multi-quantum-well, core-shell nanocolumn heterostructures can be grown on the sidewalls of the nanocolumns. Furthermore, a continuous semiconductor epitaxial layer can be formed through the overgrowth of the nanocolumns to facilitate fabrication of high-quality planar device structures or for light emitting structures.
1. A method for growing a composite nanocolumn comprising:
forming a three-faceted tetrahedron-shaped pit below a surface of a sapphire substrate wherein each facet comprises an exposed surface of a respective r-plane of the sapphire substrate;
initiating an a-plane GaN sub-nanocolumn nucleation on each facet;
promoting a growth of an a-plane GaN sub-nanocolumn on each facet toward a center of the three-facet tetrahedron-shaped pit whereby the a-plane GaN sub-nanocolumns coalesce to form an a-plane composite nanocolumn.
2. The method according to claim 1 , wherein the three-faceted tetrahedron-shaped pit is formed by wet chemical etching in a H 3 PO 4 based solution.
3. The method according to claim 2 , wherein the a-plane GaN sub-nanocolumns and a-plane composite nanocolumn have a non-polar a-plane orientation.
4. The method according to claim 1 , wherein a size of the three-faceted tetrahedron-shaped pit in a lateral dimension is sub-micron.
5. The method according to claim 1 , wherein a size of the three-faceted tetrahedron-shaped pit in a lateral dimension is in a range of 10 nanometers to 50 microns.
6. The method according to claim 1 , further comprised of a plurality of three-faceted tetrahedron-shaped pits and wherein the three-faceted tetrahedron-shaped pits are formed using a mask on the surface of the sapphire substrate to create a two-dimensional lattice pattern of three-faceted tetrahedron-shaped pits on the surface of the sapphire substrate.
7. The method according to claim 6 , wherein the a-plane GaN sub-nanocolumns and a-plane composite nanocolumn have a non-polar a-plane orientation.
8. The method according to claim 6 , wherein the a-plane sub-nanocolumns and a-plane composite nanocolumn are grown by hydride vapor phase epitaxy techniques.
9. The method according to claim 1 , wherein the a-plane composite nanocolumn comprises a Group III-nitride semiconductor material.
10. The method according to claim 1 , wherein the sapphire substrate is a c-plane sapphire substrate.
11. The method according to claim 1 , wherein the sapphire substrate is a c-plane sapphire substrate and a facet of the faceted pyramidal pit is parallel to an r-plane of the c-plane sapphire substrate.
12. The method according to claim 1 , wherein the pit is a three-faceted tetrahedron-shaped pit and the three-faceted tetrahedron-shaped pit is formed by etching the substrate in a gas mixture containing HCl.
13. The method according to claim 12 , wherein the substrate is a c-plane sapphire substrate and wherein a facet of the three-faceted tetrahedron-shaped pit is parallel to an r-plane of the c-plane sapphire substrate.
14. The method according to claim 1 , wherein the method further comprises growing a composite nanocolumn multilayer GaN and InGaN light emitting structure.
15. The method according to claim 1 , wherein the method further comprises growing a composite nanocolumn multilayer GaN and InGaN light emitting structure on the top of the composite nanocolumn.
16. The method according to claim 1 , wherein the method further comprises growing a composite nanocolumn multilayer GaN and InGaN light emitting structure on the sides of the a-plane composite nanocolumn.
17. The method according to claim 1 , wherein the method further comprises growing a composite nanocolumn multilayer GaN and AlGaN photodetector structure on the a-plane composite nanocolumn.
18. The method according to claim 1 , wherein the method further comprises growing a composite nanocolumn multilayer GaN and AlGaN photodetector structure on top of the a-plane composite nanocolumn.
19. The method according to claim 1 , wherein the method further comprises growing a composite nanocolumn multilayer GaN and AlGaN photodetector structure on sides of the a-plane composite nanocolumn.
20. The method according to claim 1 , wherein the method further comprises growing a composite nanocolumn field emission structure on the a-plane composite nanocolumn.
21. The method according to claim 1 , wherein the method further comprises growing a power device on the a-plane composite nanocolumn.
22. The method according to claim 1 further comprising growing composite nanocolumn multilayer GaN and InGaN light emitting structures on the a-plane composite nanocolumn wherein the light emitting structures emit different wavelengths based on crystallographic facets on which they are grown on the a-plane composite nanocolumn.