Methods of forming semiconductor structures

1. A method, comprising:

forming a structure comprising a first material, a blocking material, a second material in an amorphous form, and a third material in an amorphous form, the blocking material disposed between the first material and the second material, wherein at least the second material and the third material each comprise at least one element selected from the group consisting of silicon and germanium; and

exposing the structure to a temperature above a crystallization temperature of the third material and below a crystallization temperature of the second material.

2. The method of claim 1 , further comprising selecting the first material and the third material to exhibit a common chemical composition.

3. The method of claim 1 , wherein exposing the structure to a temperature above a crystallization temperature of the third material and below a crystallization temperature of the second material comprises:

crystallizing the third material; and

crystallizing the second material to form a continuous crystalline structure with the third material.

4. The method of claim 1 , wherein exposing the structure to a temperature above a crystallization temperature of the third material and below a crystallization temperature of the second material comprises converting the second material from the amorphous form to a crystalline form at a temperature below the crystallization temperature of the second material.

5. The method of claim 1 , wherein the method comprises forming a substantially continuous crystalline material having a thickness of at least about 400 Å over the blocking material.

6. The method of claim 1 , wherein exposing the structure to a temperature above a crystallization temperature of the third material and below a crystallization temperature of the second material comprises maintaining the structure at a temperature of less than about 600° C.

7. The method of claim 6 , wherein exposing the structure to a temperature above a crystallization temperature of the third material and below a crystallization temperature of the second material comprises maintaining the structure at a temperature of less than about 500° C.

8. The method of claim 1 , further comprising selecting the second material to comprise at least one dopant.

9. The method of claim 8 , further comprising selecting the second material to comprise a dopant selected from the group consisting of boron, arsenic, and phosphorus.

10. The method of claim 1 , further comprising selecting the blocking material to comprise a material selected from the group consisting of an oxide, a nitride, and a carbon-containing material.

11. The method of claim 1 , wherein exposing the structure to a temperature above a crystallization temperature of the third material and below a crystallization temperature of the second material comprises propagating a crystalline structure from the third material through the second material toward the blocking material.

12. A method, comprising:

forming a blocking material over a first material, the first material comprising at least one element selected from the group consisting of silicon and germanium;

forming a second material in an amorphous form over the blocking material, the second material comprising at least one element selected from the group consisting of silicon and germanium;

forming a third material in an amorphous form over the second material, the third material comprising at least one element selected from the group consisting of silicon and germanium, wherein the second material exhibits a crystallization temperature higher than crystallization temperatures of both the first material and the third material; and

exposing the first material, the blocking material, the second material, and the third material to a temperature above the crystallization temperatures of both the first material and the third material and below the crystallization temperature of the second material.

13. The method of claim 12 , wherein forming a second material comprises forming the second material to have a thickness between about 25 Å and about 5 μm over the blocking material.

14. The method of claim 12 , wherein forming a blocking material comprises oxidizing a surface of the first material.

15. The method of claim 12 , further comprising doping a material selected from the group consisting of the first material, the second material, and the third material.

16. The method of claim 15 , wherein doping comprises providing a dopant selected from the group consisting of boron, arsenic, and phosphorus.

17. A method, comprising:

annealing a structure comprising a first material, a blocking material, a second material in an amorphous form, and a third material in an amorphous form at a temperature above crystallization temperatures of both the first material and the third material and below a crystallization temperature of the second material;

wherein the first material, the second material, and the third material each comprise at least one element selected from the group consisting of silicon and germanium;

wherein the blocking material is between the first material and the second material; and

wherein the second material is between the blocking material and the third material.

18. The method of claim 12 , wherein exposing the first material, the blocking material, the second material, and the third material to a temperature above the crystallization temperatures of both the first material and the third material and below the crystallization temperature of the second material comprises crystallizing the second material, the second material free of a grain boundary.