Synthesis of high-purity bulk copper indium gallium selenide materials
A method for forming a high purity, copper indium gallium selenide (CIGS) bulk material is disclosed. The method includes sealing precursor materials for forming the bulk material in a reaction vessel. The precursor materials include copper, at least one chalcogen selected from selenium, sulfur, and tellurium, and at least one element from group IIIA of the periodic table, which may be selected from gallium, indium, and aluminum. The sealed reaction vessel is heated to a temperature at which the precursor materials react to form the bulk material. The bulk material is cooled in the vessel to a temperature below the solidification temperature of the bulk material and opened to release the formed bulk material. A sputtering target formed by the method can have an oxygen content of 10 ppm by weight, or less.
1. A method comprising:
sealing precursor materials for forming a bulk polycrystalline material in a reaction vessel, the precursor materials comprising copper, at least one chalcogen selected from selenium, sulfur, and tellurium, and at least one element selected from gallium, indium, and aluminum;
heating the sealed reaction vessel to a temperature at which the precursor materials react to form the bulk material, wherein the heating is to a maximum temperature of 776° C., wherein the heating includes:
ramping the temperature of the sealed vessel to a first soak temperature;
maintaining the first soak temperature for a sufficient time for at least some chalcogen in at least one of liquid and vapor form to react with other precursor materials;
ramping the temperature from the first soak temperature to a second soak temperature; and
maintaining the second soak temperature for sufficient time to form the bulk material; and
at a temperature at which the bulk material is solid, opening the reaction vessel and removing the formed bulk material.
2. The method of claim 1 , wherein the sealing of the precursor materials comprises sealing the copper, chalcogen, and the at least one of gallium and indium in the vessel in their elemental form.
3. The method of claim 1 , wherein the chalcogen is predominantly selenium.
4. The method of claim 1 , wherein the bulk material has a general formula Cu a (Z)M 2+b ,
where Z is selected from In, Ga, Al, and combinations thereof,
M is selected from Se, S, Te, and combinations thereof,
0.9≤a≤1.1, and
−0.4≤b≤+0.4.
5. The method of claim 1 , wherein the bulk material includes chalcogen in excess of a stoichiometric amount.
6. The method of claim 1 , further comprising, prior to the sealing, purifying the chalcogen to reduce a concentration of oxygen impurities.
7. The method of claim 1 , wherein the second soak temperature is in a temperature range of 700° C. to 775° C.
8. The method of claim 1 , wherein the method further includes combining a dopant with the precursor materials, the dopant being selected from Na, Li, Cr, Ni, Ti, and combinations thereof.
9. The method of claim 8 , wherein the dopant is present at no more than 10 atomic % of the precursor materials and dopant in the vessel.
10. The method of claim 1 , wherein the sealing includes evacuating the vessel containing the precursor materials prior to sealing the vessel.
11. The method of claim 1 , wherein the reaction vessel is formed from a refractory material having a melting point of at least 1300° C.
12. The method of claim 11 , wherein the refractory material comprises silica.
13. The method of claim 1 , wherein the reaction vessel includes an interior width of at least 5 cm.
14. The method of claim 1 , wherein the bulk material comprises a monolith.
15. The method of claim 14 , wherein the monolith is cylindrical.
16. The method of claim 1 , further comprising sputtering the bulk material onto a substrate to form a semiconductor thin film.