Low threading dislocation density relaxed mismatched epilayers without high temperature growth
A semiconductor structure and method of processing same including a substrate, a lattice-mismatched first layer deposited on the substrate and annealed at a temperature greater than 100° C. above the deposition temperature, and a second layer deposited on the first layer with a greater lattice mismatch to the substrate than the first semiconductor layer. In another embodiment there is provided a semiconductor graded composition layer structure on a semiconductor substrate and a method of processing same including a semiconductor substrate, a first semiconductor layer having a series of lattice-mismatched semiconductor layers deposited on the substrate and annealed at a temperature greater than 100° C. above the deposition temperature, a second semiconductor layer deposited on the first semiconductor layer with a greater lattice mismatch to the substrate than the first semiconductor layer, and annealed at a temperature greater than 100° C. above the deposition temperature of the second semiconductor layer.
1. A method of processing a semiconductor structure, the method comprising the steps of:
depositing onto a substrate, at a deposition temperature, a first layer disposed across the substrate, lattice mismatched whit respect to the substrate, and having a first dislocation density; and
following a deposition annealing the first lattice-mismatched layer at an annealing temperature higher than the deposition temperature so as to lower the first dislocation density.
2. The method of claim 1 , wherein said lattice mismatched first layer is deposited by chemical vapor deposition.
3. The method of claim 1 further comprising the step of:
(a) depositing, at a subsequent deposition temperature, a subsequent layer having a dislocation density;
(b) following the deposition, annealing the subsequent layer at a subsequent annealing temperature higher than the subsequent deposition temperature so as to lower the dislocation density of the subsequent layer, and
(c) repeating the steps (a) and (b).
4. The method of claim 3 wherein the subsequent layer is lattice-mismatched with respect to the substrate.
5. The method of claim 4 wherein the subsequent layer lattice-mismatch is greater than the previously deposited layer lattice-mismatch.
6. The method of claim 3 , wherein said substrate has at least a surface layer comprising GaAs and said first and subsequent layer comprise In y Ga 1-y As.
7. The method of claim 3 , wherein said substrate has at least a surface layer comprising Gap and said first and subsequent layers comprise In x Ga 1-x P.
8. The method of claim 3 , wherein the substrate has at least a surface layer comprising Si, the first and subsequent layer comprise Si 1-x Ge x , and sequential layers in the at least one of the first and subsequent layers differ in Ge concentration by approximately 1.5%, the growth temperature is approximately 750° C., and the anneal temperature is approximately 1050° C.
9. The method of claim 3 , wherein the substrate has at least a surface layer comprising Si, the first and subsequent layers comprising Si 1-x Ge x , and subsequential layers in the at least one of the first and subsequent layers differ in Ge concentration by approximately 1.5%, the growth temperature is approximately 750° C., and the anneal temperature is approximately 1050° C., and the anneal time is greater than 0.1 seconds.
10. The method of claim 3 , wherein said substrate has at least a surface layer comprising Si and said first and subsequent layers comprise Si 1-x Ge x .
11. The method of claim 10 , wherein said first and subsequent layers differ by a Ge concentration less than 10% Ge.
12. The method of claim 10 , wherein said first and subsequent layers differ in Ge concentration by approximately 1.5% Ge.
13. The method of claim 10 , wherein said first and subsequent layers of Si 1-x Ge x are deposited at a growth temperature less than 850° C.
14. The method of claim 10 , wherein said annealing occurs at a temperature greater than 900° C.
15. The method of claim 10 , wherein anneal time is greater than 0.1 seconds.
16. The method of claim 10 , wherein said first and subsequent layers differ in Ge concentration by approximately 1.5%, the growth temperature is approximately 750° C., and the anneal temperature is approximately 1050° C.
17. The method of claim 10 , wherein said first and subsequent layers differ in Ge concentration by approximately 1.5%, the growth temperature is approximately 750° C., and the anneal temperature is approximately 1050° C., and the anneal time is greater than 0.1 seconds.
18. The method of claim 1 wherein annealing temperature exceeds the deposition temperature by at least 100° C.
19. The method of claim 18 wherein the deposition step comprises providing a deposition source gas, and the annealing step occurs in the absence of the deposition source gas.
20. The method of claim 1 , wherein anneal time is less than 1 minute.