Epitaxial growth of CZT(S,Se) on silicon
Techniques for epitaxial growth of CZT(S,Se) materials on Si are provided. In one aspect, a method of forming an epitaxial kesterite material is provided which includes the steps of: selecting a Si substrate based on a crystallographic orientation of the Si substrate; forming an epitaxial oxide interlayer on the Si substrate to enhance wettability of the epitaxial kesterite material on the Si substrate, wherein the epitaxial oxide interlayer is formed from a material that is lattice-matched to Si; and forming the epitaxial kesterite material on a side of the epitaxial oxide interlayer opposite the Si substrate, wherein the epitaxial kesterite material includes Cu, Zn, Sn, and at least one of S and Se, and wherein a crystallographic orientation of the epitaxial kesterite material is based on the crystallographic orientation of the Si substrate. A method of forming an epitaxial kesterite-based photovoltaic device and an epitaxial kesterite-based device are also provided.
1. A method of forming an epitaxial kesterite material, comprising the steps of:
selecting a silicon (Si) substrate based on a crystallographic orientation of the Si substrate;
forming an epitaxial oxide interlayer on the Si substrate to enhance wettability of the epitaxial kesterite material on the Si substrate, wherein the epitaxial oxide interlayer comprises a material that is lattice-matched to Si; and
forming the epitaxial kesterite material on a side of the epitaxial oxide interlayer opposite the Si substrate, wherein the epitaxial kesterite material comprises copper (Cu), zinc (Zn), tin (Sn), and at least one of sulfur (S) and selenium (Se), wherein the epitaxial oxide interlayer is configured to prevent etching of the Si substrate during the step of forming of the epitaxial kesterite material, and wherein a crystallographic orientation of the epitaxial kesterite material is based on the crystallographic orientation of the Si substrate such that the crystallographic orientation of the epitaxial kesterite material is controlled by selecting the Si substrate having a particular crystallographic orientation.
2. The method of claim 1 , further comprising the step of:
selecting the Si substrate from one of a Si(001) substrate and a Si(111) substrate.
3. The method of claim 1 , wherein the epitaxial oxide interlayer is formed having a thickness of from about 5 nanometers to about 30 nanometers, and ranges therebetween.
4. The method of claim 1 , wherein the epitaxial oxide interlayer completely covers a surface of the Si substrate on which the epitaxial kesterite material is formed.
5. The method of claim 1 , wherein the epitaxial oxide interlayer comprises erbium oxide (Er 2 O 3 ), lanthanum oxide (La 2 O 3 ), or yttrium oxide (Y 2 O 3 ) each of which is lattice-matched to Si.
6. The method of claim 1 , wherein the step of forming the epitaxial oxide interlayer and the step of forming the epitaxial kesterite material are performed by evaporation in a vacuum chamber in-situ without breaking vacuum between deposition of the epitaxial oxide interlayer and the epitaxial kesterite material.
7. The method of claim 6 , further comprising the steps of:
cleaning the Si substrate; and
placing the Si substrate, once cleaned, in the vacuum chamber.
8. The method of claim 6 , wherein the step of forming the epitaxial oxide interlayer is performed in the vacuum chamber at a pressure of from about 1×10 −6 Torr to about 1×10 −9 Torr, and ranges therebetween, at a temperature of from about 500° to about 750°, and ranges therebetween.
9. The method of claim 6 , wherein the step of forming the epitaxial kesterite material is performed in the vacuum chamber at a pressure of from about 1×10 −6 Torr to about 1×10 −9 Torr, and ranges therebetween, at a temperature of from about 350° C. to about 550° C., and ranges therebetween.
10. A method of forming an epitaxial kesterite-based photovoltaic device, comprising the steps of:
selecting a Si substrate based on a crystallographic orientation of the Si substrate;
forming an epitaxial kesterite material on the Si substrate which serves as an absorber layer of the photovoltaic device, wherein the epitaxial kesterite material comprises Cu, Zn, Sn, and at least one of S and Se, and wherein a crystallographic orientation of the epitaxial kesterite material is based on the crystallographic orientation of the Si substrate such that the crystallographic orientation of the epitaxial kesterite material is controlled by selecting the Si substrate having a particular crystallographic orientation;
forming a buffer layer on a side of the epitaxial kesterite material opposite the Si substrate; and
forming a transparent front contact on a side of the buffer layer opposite the epitaxial kesterite material.
11. The method of claim 10 , further comprising the step of:
forming an epitaxial oxide interlayer on the Si substrate such that the epitaxial oxide interlayer is present between the Si substrate and the epitaxial kesterite material, wherein the epitaxial oxide interlayer enhances wettability of the epitaxial kesterite material on the Si substrate, wherein the epitaxial oxide interlayer is configured to prevent etching of the Si substrate during the step of forming of the epitaxial kesterite material, and wherein the epitaxial oxide interlayer comprises a material that is lattice-matched to Si.
12. The method of claim 11 , wherein the epitaxial oxide interlayer is formed having a thickness of from about 5 nanometers to about 30 nanometers, and ranges therebetween.
13. The method of claim 11 , wherein the epitaxial oxide interlayer completely covers a surface of the Si substrate onto which the epitaxial kesterite material is formed.
14. The method of claim 11 , wherein the epitaxial oxide interlayer comprises Er 2 O 3 , La 2 O 3 , or Y 2 O 3 each of which is lattice-matched to Si.
15. The method of claim 10 , further comprising the step of:
selecting the Si substrate from one of a Si(001) substrate and a Si(111) substrate.
16. The method of claim 10 , wherein the buffer layer comprises cadmium sulfide (CdS), a cadmium-zinc-sulfur material of the formula Cd 1-x Zn x S (wherein 0<x≦1), indium sulfide (In 2 S 3 ), zinc oxide, zinc oxysulfide, or aluminum oxide (Al 2 O 3 ).
17. The method of claim 10 , wherein the transparent front contact comprises at least one of indium-tin-oxide (ITO) and aluminum doped zinc oxide (AZO).
18. An epitaxial kesterite-based device, comprising:
a Si substrate;
an epitaxial oxide interlayer on the Si substrate, wherein the epitaxial oxide interlayer comprises a material that is lattice-matched to Si; and
an epitaxial kesterite material on a side of the epitaxial oxide interlayer opposite the Si substrate, wherein the epitaxial oxide interlayer serves to enhance wettability of the epitaxial kesterite material on the Si substrate, wherein the epitaxial kesterite material comprises Cu, Zn, Sn, and at least one of S and Se, wherein a crystallographic orientation of the epitaxial kesterite material is based on the crystallographic orientation of the Si substrate, and wherein the epitaxial oxide interlayer completely covers a surface of the Si substrate onto which the epitaxial kesterite material is formed and serves to prevent etching of the Si substrate.
19. The epitaxial kesterite-based device of claim 18 , wherein the epitaxial oxide interlayer comprises Er 2 O 3 , La 2 O 3 , or Y 2 O 3 each of which is lattice-matched to Si, and wherein the epitaxial oxide interlayer has a thickness of from about 5 nanometers to about 30 nanometers, and ranges therebetween.
20. The epitaxial kesterite-based device of claim 18 , further comprising:
a buffer layer on a side of the epitaxial kesterite material opposite the Si substrate; and
a transparent front contact on a side of the buffer layer opposite the epitaxial kesterite material.