Methods for fabricating and etching porous silicon carbide structures
The present disclosure relates to methods of fabricating a porous structure, such as a porous silicon carbide structure. The methods can include a step of providing a structure to be rendered porous, and a step of providing an etching solution. The methods can also include a step of electrochemically etching the structure to produce pores through at least a region of the structure, resulting in the formation of a porous structure. The morphology of the porous structure can be controlled by one or more parameters of the electrochemical etching process, such as the strength of the etching solution and/or the applied voltage.
1. A method of fabricating a porous silicon carbide structure having a selected morphology, comprising:
providing a silicon carbide structure;
providing an etching solution comprising a reducing agent and an oxidizing agent;
electrochemically etching the silicon carbide structure with the etching solution to produce pores through a region of the silicon carbide structure to form a porous silicon carbide structure, wherein electrochemically etching the silicon carbide structure comprises applying a voltage to a surface of the silicon carbide structure to produce a current through the region of the silicon carbide structure; and
controlling an etch propagation rate of the etching solution through the region of the silicon carbide structure to achieve the selected morphology by changing at least one fabrication parameter including one or more of concentration of reducing agent, voltage, and use of a surfactant, wherein the current decreases at a substantially constant rate during the electrochemical etching step.
2. The method of claim 1 , wherein the silicon carbide structure comprises a 3C, 4H, or 6H polytype of silicon carbide.
3. The method of claim 1 , wherein the silicon carbide structure comprises a silicon carbide semiconductor.
4. The method of claim 1 , wherein the silicon carbide structure comprises a predefined electronic carrier concentration.
5. The method of claim 1 , wherein the silicon carbide structure comprises a predefined crystalline designation.
6. The method of claim 1 , wherein the oxidizing agent comprises water, an alcohol, hydrogen peroxide, or a mixture thereof.
7. The method of claim 1 , wherein the reducing agent comprises hydrofluoric acid.
8. The method of claim 7 , wherein the concentration of the hydrofluoric acid is from about 1% to about 50%, from about 1% to about 20%, from about 1% to about 15%, from about 1% to about 10%, from about 1% to about 5%, or from about 2% to about 5%, by volume.
9. The method of claim 7 , wherein the etch propagation rate is dependent upon the concentration of the hydrofluoric acid.
10. The method of claim 7 , wherein the concentration of hydrofluoric acid is inversely proportional to a porosity of the porous silicon carbide structure.
11. The method of claim 1 , wherein the etching solution further comprises a surfactant.
12. The method of claim 1 , wherein the voltage is from about 20 V to about 40 V, from about 20 V to about 30 V, or from about 20 V to about 26 V.
13. The method of claim 1 , wherein the current is proportional to a removal rate of the material.
14. The method of claim 1 , wherein the selected morphology comprises at least one of a selected average pore diameter, a selected pore wall thickness, or a selected porosity.
15. The method of claim 1 , wherein the selected morphology comprises an average pore wall thickness of between about 2 nm and about 200 nm.
16. The method of claim 1 , wherein the selected morphology comprises an average pore diameter of between about 0.1 μm and about 3 μm.
17. The method of claim 1 , wherein the selected morphology comprises an average pore diameter of between about 0.1 μm and about 3 μm, and an average pore wall thickness of between about 2 nm and about 200 nm.
18. The method of claim 1 , wherein the selected morphology comprises a porosity of from about 60% to about 96%.
19. The method of claim 1 , wherein the selected morphology comprises a substantially uniform material density.