Highly aligned vertical GaN nanowires using submonolayer metal catalysts
A method for forming vertically oriented, crystallographically aligned nanowires (nanocolumns) using monolayer or submonolayer quantities of metal atoms to form uniformly sized metal islands that serve as catalysts for MOCVD growth of Group III nitride nanowires.
1. A method for fabricating vertically oriented nanowires on a substrate, the method comprising:
depositing up to approximately a monolayer of catalyst metal atoms on a surface of a crystallographic template substrate;
heating the crystallographic template substrate to induce surface diffusion of the catalyst metal atoms to form a plurality of metal nanoclusters; and
reacting gallium atom precursor molecules and nitrogen precursor molecules at the metal nanoclusters to form vertically oriented single-crystal gallium nitride nanowires epitaxially aligned with the crystallographic template substrate, wherein the ratio of nitrogen precursor molecules to gallium atom precursor molecules is greater than 1.
2. The method of claim 1 , wherein a submonolayer of catalyst metal atoms is deposited using a metal evaporation technique and wherein a nominal thickness of catalyst metal is less than or equal to approximately 3 Å.
3. The method of claim 1 , wherein the step of heating the crystallographic template substrate is performed under a reducing atmosphere.
4. The method of claim 1 , wherein the gallium atom precursor molecules are selected from the group consisting of trimethylgallium, triethylgallium, gallium-containing hydrocarbon compounds, gallium, gallium oxide, and gallium nitride.
5. The method of claim 1 , wherein the nitrogen precursor molecules are selected from the group consisting of ammonia, and nitrogen.
6. The method of claim 1 , wherein the catalyst metal atoms are selected from the group consisting of Ni, Au, Pt, Ga, In, Co, and Fe.
7. The method of claim 1 , wherein the step of reacting is performed at a temperature between approximately 650° C. and approximately 850° C.
8. The method of claim 1 , wherein the crystallographic template substrate is selected from the group consisting of r-plane sapphire and a substrate comprising a surface layer of epitaxially grown GaN.