Methods and structures for relaxation of strained layers

1. A method for relaxing a layer of a strained material comprising:

growing the strained-material layer on a seed substrate;

depositing a first low-viscosity layer on one exposed face of the strained-material layer;

bonding a first substrate to the first low-viscosity layer;

detaching the strained-material layer, the first low-viscosity layer, and the first substrate from the seed substrate;

depositing a second low-viscosity layer on other now-exposed face of the strained-material layer;

bonding a second substrate to the second low-viscosity layer so as to form a sandwich structure; and

subjecting the sandwich structure to heat treatment at a temperature of between 800° C. and 950° C. to cause reflow of one or both of the first and the second low-viscosity layers so as to at least partly relax the strained-material layer within the sandwich structure.

2. A method for the manufacture of semiconductor substrates suitable for the fabrication of LED devices, laser devices, or photovoltaic field devices, the method comprising:

forming a layer of an at least partially relaxed strained material according to the method of claim 1 ;

exposing at least a portion of the layer of partially relaxed strained material; and

growing epitaxially on the exposed portion of the at least partially relaxed strained material layer a further layer comprising a semiconductor material suitable for the fabrication of one or more LED devices, laser devices, and photovoltaic field devices.

3. The method according to claim 2 , wherein the at least partially relaxed layer of strained material comprises a polar Group III-nitride material, and wherein at least portions of the exposed face of the further layer have Group III polarity.

4. The method of claim 1 , wherein the material of the strained-material layer of the sandwich structure is strained InGaN.

5. The method of claim 4 , wherein the at least partially relaxed layer of strained InGaN is arranged in a plurality of islands separated by trenches.

6. The method of claim 4 , which further comprises bonding a substrate to each low viscosity layer of the sandwich structure.

7. The method of claim 6 , wherein either or both substrates are sapphire or silicon.

8. The method of claim 1 , wherein the first and the second substrates have coefficients of thermal expansion that differ from each other by less than 10%.

9. The method of claim 1 , further comprising, before performing the heat treatment, patterning the strained-material layer so as to form separated islands of strained-material at least a majority of which have lateral dimensions larger than 0.25 mm 2 .

10. The method of claim 9 , wherein the patterning is performed prior to depositing the second low-viscosity layer.

11. The method of claim 9 , wherein the patterning is performed subsequent to depositing the second low-viscosity layer on the strained-material layer, and wherein both the strained-material layer and the second low-viscosity layer are jointly patterned.

12. The method of claim 1 , wherein the strained-material layer comprises a Group III-nitride material or an alloy or mixture thereof.

13. The method of claim 1 , wherein the one or both of the low-viscosity layers comprise a composition or mixture including SiO 2 and one or both of boron and phosphorous.

14. The method of claim 13 , wherein the composition comprises less than 5% by weight of boron.

15. The method of claim 1 wherein at least a portion of the heat treatment is performed at a temperature of less than 850° C.

16. The method of claim 1 , wherein one or both of the low-viscosity layers comprise an absorption layer suitable for promoting the detachment of a substrate bonded thereto.