Metal chalcogenide aqueous precursors and processes to form metal chalcogenide films
Metal chalcogenide precursor solutions are described that comprise an aqueous solvent, dissolved metal formate salts and a chalcogenide source composition. The chalcogenide source compositions can be organic compounds lacking a carbon-carbon bond. The precursors are designed to form a desired metal chalcogenide upon thermal processing into films with very low levels of contamination. Potentially contaminating elements in the precursors form gaseous or vapor by-products that escape from the vicinity of the product metal chalcogenide films.
1. A metal chalcogenide precursor solution comprising an aqueous solvent having dissolved a metal cation, formate anions, and a chalcogenide composition selected from the group consisting of thiourea, thioformamide, selenourea, selenoformamide and a combination thereof, wherein the total cation concentration is from about 0.01 molar to about 3.0 molar.
2. The metal chalcogenide precursor solution of claim 1 wherein the solution comprises a d-block metal cation and a p-block metal cation.
3. The metal chalcogenide precursor solution of claim 2 wherein the d-block metal cation comprises copper.
4. The metal chalcogenide precursor solution of claim 2 wherein the p-block metal cation comprise aluminum, gallium, indium or a combination thereof.
5. The metal chalcogenide precursor solution of claim 1 wherein the solvent comprises formic acid.
6. The metal chalcogenide precursor solution of claim 1 wherein the solvent comprises water and an alcohol.
7. The metal chalcogenide precursor solution of claim 1 wherein the chalcogenide composition comprises thiourea.
8. The metal chalcogenide precursor solution of claim 1 wherein the chalcogenide composition comprises selenourea.
9. The metal chalcogenide precursor solution of claim 1 wherein the concentration of the chalcogenide composition is from about 0.03 molar to about 15.0 molar.
10. The metal chalcogenide precursor solution of claim 1 wherein the solution has a pH from about 2.0 to about 4.0.
11. A method for preparing an aqueous precursor of a metal chalcogenide, the method comprising forming an aqueous solution comprising a metal cation, formate anions, and a chalcogenide composition selected from the group consisting of thiourea, thioformamide, selenourea, selenoformamide or a combination of thereof, wherein the total cation concentration is from about 0.01 molar to about 3.0 molar.
12. The method of claim 11 wherein the metal cation comprises a d-block metal cation and a p-block metal cation.
13. The method of claim 11 wherein the forming of the aqueous solution comprises adding metal formate salts to an aqueous solution of the chalcogenide composition.
14. The method of claim 11 further comprising adjusting the concentration of aqueous precursor solution by providing for the evaporation of a selected amount of solvent to achieve a desired concentration.
15. The metal chalcogenide precursor solution of claim 1 wherein the surface tension of the solution ranges from about 72 mN/m to about 37 mN/m.
16. The method of claim 11 wherein the solution has a pH from about 2.0 to about 4.0.
17. The method of claim 11 wherein the solution comprises formic acid.