Growth of planar reduced dislocation density
View Patent ↗A method of growing highly planar, fully transparent and specular m-plane gallium nitride (GaN) films. The method provides for a significant reduction in structural defect densities via a lateral overgrowth technique. High quality, uniform, thick m-plane GaN films are produced for use as substrates for polarization-free device growth.
1. A method of growing planar m-plane gallium nitride (GaN) films, comprising:
(a) performing a direct growth of a planar m-plane GaN film by hydride vapor phase epitaxy; and
(b) performing a lateral epitaxial overgrowth (LEO) off of a surface of the direct growth resulting in a top surface that is a planar m-plane GaN film.
2. The method of claim 1 , wherein the planar m-plane GaN film is produced for use as a substrate for polarization-free device growth.
3. The method of claim 1 , wherein the direct growth of the planar m-plane GaN film is performed on a substrate comprising m-plane SiC, (100)γ-LiAlO 2 , or a substrate covered by an m-plane (In,Al,Ga,B)N template layer.
4. The method of claim 1 , wherein the performing step (a) further comprises:
(1) loading a substrate into a reactor;
(2) heating the reactor to a growth temperature, with a mixture of ammonia (NH 3 ), hydrogen (H 2 ) and nitrogen (H 2 ) flowing into a growth chamber;
(3) reducing the reactor's pressure to a desired deposition pressure, wherein the desired deposition pressure is below atmospheric pressure;
(4) initiating a gaseous hydrogen chloride (HCl) flow to a gallium (Ga) source to begin growth of the planar m-plane GaN film directly on the substrate, wherein the gaseous HCl reacts with the Ga to form gallium monochloride (GaCl);
(5) transporting the GaCl to the substrate using a carrier gas that includes at least a fraction of hydrogen (H 2 ), wherein the GaCl reacts with ammonia (NH 3 ) at the substrate to form the planar m-plane GaN film; and
(6) after a desired growth time has elapsed, interrupting the gaseous HCl flow, returning the reactor's pressure to atmospheric pressure, and reducing the reactor's temperature to room temperature.
5. The method of claim 4 , wherein the substrate is coated wit a nucleation layer deposited either at low temperatures or at the growth temperature.
6. The method of claim 4 , further comprising nitridating the substrate by adding anhydrous ammonia (NH 3 ) to a gas stream in the reactor.
7. The method of claim 4 , wherein the interrupting step (6) further comprises including anhydrous ammonia (NH 3 ) in a gas stream to prevent decomposition of the GaN film during the reduction of the reactor's temperature.
8. The method of claim 4 , wherein the interrupting step (6) further comprises cooling the substrate at a reduced pressure.
9. The method of claim 1 , wherein the performing step (b) further comprises:
(1) patterning a mask deposited on the surface of the direct growth; and
(2) performing a lateral epitaxial overgrowth off the surface of the direct growth using hydride vapor phase epitaxy, wherein GaN nucleates only on portions of the surface of the direct growth not covered by the patterned mask, the GaN grows vertically through openings in the patterned mask, and the GaN then spreads laterally above the patterned mask and across the surface of the direct growth.
10. The method of claim 9 , wherein the lateral epitaxial overgrowth utilizes growth pressures of approximately atmospheric pressure or below, and a carrier gas containing a fraction of hydrogen.
11. The method of claim 10 , wherein the carrier gas is predominantly hydrogen.
12. The method of claim 11 , wherein the carrier gas comprises a mixture of hydrogen and nitrogen, argon, or helium.
13. The method of claim 9 , wherein the lateral epitaxial overgrowth reduces threading dislocations and defect densities in the planar m-plane GaN film.
14. The method of claim 9 , wherein the patterned mask is comprised of a metallic material or a dielectric material.
15. The method of claim 9 , wherein the patterning step comprises:
depositing a silicon dioxide (SiC 2 ) film on the surface of the direct growth;
patterning a photoresist layer on the silicon dioxide film;
etching away any portions of the silicon dioxide film exposed by the patterned photoresist layer;
removing remaining portions of the photoresist layer; and
cleaning the surface of the direct growth.
16. The method of claim 9 , wherein the surface of the direct growth is coated with a nucleation layer deposited at either low temperatures or at the growth temperature.
17. The method of claim 1 , wherein the lateral epitaxial overgrowth comprises:
(1) etching pillars or stripes out of the surface of the direct growth; and
(2) growing laterally from the pillars or stripes.
18. The method of claim 1 , wherein the lateral epitaxial overgrowth comprises:
(1) etching pillars or stripes out of the surface of the direct growth;
(2) masking an upper surface of the pillars or stripes; and
(3) growing laterally from exposed portions of the masked upper surface of the pillars or stripes.
19. A device manufactured using the method of claim 1 .