Alkali semi-metal films and method and apparatus for fabricating them

1. A method for synthesizing an alkali semi-metal compound, wherein a semi-metal is a semi-metal in Group 15, the method comprising:

mixing, at a temperature from about 15° C. to about 30° C. and at an ambient pressure from about 750 torr to about 800 torr, least two alkali materials to form an alloy composition; and

mixing, at a temperature from about 15° C. to about 30° C. and at an ambient pressure from about 750 torr to about 800 torr, a solid semi-metal material and the alloy composition to form the alkali semi-metal compound;

wherein the at least two alkali materials comprise a first alkali material and a second alkali material; and wherein the alkali semi-metal compound is a crystal compound.

2. The method of claim 1 wherein the alloy composition is a liquid alloy composition.

3. The method of claim 1 wherein the semi-metal material is antimony.

4. The method of claim 3 , wherein the first alkali material comprises potassium (K), the second alkali material comprises cesium (Cs), the liquid alloy composition comprises K 2 Cs, and the ternary crystal compound comprises K 2 CsSb.

5. The method of claim 1 , wherein the method is performed in an enclosed environment.

6. The method of claim 5 , wherein the enclosed environment is a non-oxidizing environment containing inert gas, and wherein the enclosed environment is purified to contain less than about 0.5 ppm of oxygen (O 2 ) and water (H 2 O).

7. The method of claim 6 wherein the inert gas is nitrogen or argon.

8. The method of claim 1 , further comprising, upon mixing the solid semi-metal material and the liquid alloy composition, spontaneously forming the crystal compound without external physical interference.

9. The method of claim 1 , wherein the alkali semi-metal compound comprises a nano-crystalline grain structure.

10. A method for fabricating a thin film component, comprising:

providing pre-synthesized semi-metal compound material, the semi-metal compound material comprising one or more alkali materials and a semi-metal material;

wherein the alkali semi-metal compound is a crystal compound;

wherein pre-synthesizing the semi-metal compound material comprises:

mixing, at a temperature from about 15° C. to about 30° C. and at an ambient pressure from about 750 torr to about 800 torr, at least two alkali materials to form an alloy composition; and

mixing, at a temperature from about 15° C. to about 30° C. and at an ambient pressure from about 750 torr to about 800 torr, a solid semi-metal material and the alloy composition to form the alkali semi-metal compound; and

A) depositing a thin film of the semi-metal compound material on a substrate to form the thin film component.

11. The method of claim 10 wherein the semi-metal material is antimony.

12. The method of claim 10 wherein the thin film component is a photocathode.

13. The method of claim 12 further comprising:

B) measuring a quantum efficiency of the cathode; and

C) repeating A) and B) until the quantum efficiency is greater than a predetermined value.

14. The method of claim 13 , wherein B) comprises:

B1) applying an electric bias between an anode and the cathode;

B2) illuminating a light of a wavelength to the cathode; and

B3) measuring a photocurrent between the anode and the cathode as a function of the wavelength to obtain the quantum efficiency.

15. The method of claim 14 , wherein the anode comprises a metallic ring configured to stay remote from a location of the semi-metal compound material and proximate the cathode.

16. The method of claim 10 , wherein the at least two alkali materials are a first alkali material and a second alkali material.

17. The method of claim 16 , wherein the first alkali material comprises potassium (K), and the second alkali material comprises cesium (Cs).

18. The method of claim 17 wherein the semi-metal material is antimony, and wherein the semi-metal compound material comprises K 2 CsSb.

19. The method of claim 16 , wherein the first alkali material comprises potassium (K), the second alkali material comprises cesium (Cs), and the liquid alloy composition comprises K 2 Cs.

20. The method of claim 10 , wherein A) comprises:

A1) depositing the thin film of the semi-metal compound material using one of a hot wall evaporation apparatus, sputtering and an e-beam deposition apparatus.

21. The method of claim 10 wherein the alloy composition is a liquid alloy composition.

22. The method of claim 10 further comprising co-evaporating, during deposition, at least one alkali material from the at least two alkali materials in order to alter alkali concentration along a direction perpendicular to the substrate.

23. The method of claim 10 further comprising, before deposition, preparing the substrate in order to obtain a predetermined crystallographic surface orientation.

24. The method of claim 10 wherein the thin film component is a photovoltaic component.

25. A method fabricating a thin film component, the method comprising:

providing pre-synthesized semi-metal compound material, the semi-metal compound material comprising one or more alkali materials and a semi-metal material; and

depositing a thin film of the semi-metal compound material on a substrate to form the thin film component;

co-evaporating, during deposition, at least one alkali material from the one or more alkali materials in order to alter alkali concentration along a direction perpendicular to the substrate;

activating a portion of the at least one alkali material by collisions in a sputter plasma;

applying a bias voltage on the substrate in order to preselect activated alkali implementation;

keeping the substrate at a predetermined temperature during deposition in order to prevent migration and to preserve a doping profile; and

annealing the thin film component by heating at a predetermined temperature for a predetermined time.

26. The method of claim 25 wherein the at least one alkali material is cesium (Cs).

27. A method for fabricating a thin film component, comprising:

providing pre-synthesized semi-metal compound material, the semi-metal compound material comprising one or more alkali materials and a semi-metal material;

before deposition, preparing a substrate in order to obtain a predetermined crystallographic surface orientation; and

depositing a thin film of the semi-metal compound material on the substrate to form the thin film component;

wherein preparing the substrate comprises:

depositing a number of monolayers of cesium on the substrate;

depositing a monolayer of the semi-metal material on an outer monolayer from the number of monolayers of cesium; and

heating the substrate to a predetermined temperature for a predetermined time.

28. The method of claim 27 further comprising:

co-evaporating, during deposition, at least one alkali material from the one or more alkali materials in order to alter alkali concentration along a direction perpendicular to the substrate;

activating a portion of the at least one alkali material by collisions in a sputter plasma;

applying a bias voltage on the substrate in order to preselect activated alkali implementation;

keeping the substrate at a predetermined temperature during deposition in order to prevent migration and to preserve a doping profile;

forming a Delta layer with n-doping on an outer surface of the thin film component; and

curing the thin film component by heating for a second predetermined time configured to prevent interdiffusion and pumping for a third predetermined time.

29. The method of claim 28 wherein forming the Delta layer with n-doping comprises stopping deposition and evaporating the at least one alkali while the substrate is at a second predetermined temperature.

30. The method of claim 29 wherein deposition was by sputtering and wherein the at least one alkali is cesium (Cs).

31. A method for fabricating a target for depositing an alkali semi-metal compound, the method comprising:

loading the alkali semi-metal compound onto a target holder, wherein a semi-metal is a semi-metal in Group 15, synthesized by the method of:

mixing at least two alkali materials to form an alloy composition; and

mixing a solid semi-metal material and the alloy composition to form the alkali semi-metal compound;

wherein the alloy composition is a liquid alloy composition;

wherein the one or more alkali materials comprise a first alkali material and a second alkali material; and wherein the alkali semi-metal compound is a crystal compound;

forming a film from the alkali semi-metal compound by pressing and packing; and

depositing a layer of a passivating material on a top surface of the film.

32. The method of claim 31 wherein the semi-metal material is antimony.

33. The method of claim 32 wherein the passivating material is antimony.

34. The method of claim 31 wherein the method is practiced in a glove box.

35. The method of claim 31 further comprising:

removing the layer of passivating material before deposition.