Gallium nitride devices with aluminum nitride intermediate layer
View Patent ↗The invention provides semiconductor materials including a gallium nitride material layer formed on a silicon substrate and methods to form the semiconductor materials. The semiconductor materials include a transition layer formed between the silicon substrate and the gallium nitride material layer. The transition layer is compositionally-graded to lower stresses in the gallium nitride material layer which can result from differences in thermal expansion rates between the gallium nitride material and the substrate. The lowering of stresses in the gallium nitride material layer reduces the tendency of cracks to form. Thus, the invention enables the production of semiconductor materials including gallium nitride material layers having few or no cracks. The semiconductor materials may be used in a number of microelectronic and optical applications.
1. A semiconductor structure comprising:
a substrate;
an intermediate layer comprising aluminum nitride formed above said substrate, said intermediate layer being substantially free of gallium;
a transition layer including at least one compositionally-graded layer and a superlattice;
a gallium nitride layer formed over said transition layer.
2. The semiconductor structure of claim 1 wherein said intermediate layer comprises an aluminum nitride alloy situated between said aluminum nitride and said substrate.
3. The semiconductor structure of claim 1 wherein said at least one compositionally-graded layer is graded discontinuously across the thickness of the layer.
4. The semiconductor structure of claim 1 wherein said transition layer comprises an alloy of gallium nitride selected from the group consisting of Al X In Y Ga (1-X-Y) N, In Y Ga (1-Y) N, and Al X Ga (1-X) N.
5. The semiconductor structure of claim 4 wherein a concentration of gallium in said transition layer is graded.
6. The semiconductor structure of claim 4 wherein x is varied from a first value at a back surface of said transition layer to a second value at a front surface of said transition layer.
7. The semiconductor structure of claim 4 wherein y is varied from a first value at a back surface of said transition layer to a second value at a front surface of said transition layer.
8. The semiconductor structure of claim 1 wherein said substrate comprises a silicon-on-insulator (SOI) substrate.
9. The semiconductor structure of claim 1 wherein said substrate comprises a silicon-on-sapphire (SOS) substrate.
10. The semiconductor structure of claim 1 wherein said substrate comprises a SIMOX substrate.
11. A semiconductor structure comprising:
a substrate;
an intermediate layer comprising aluminum nitride formed over at least one layer, said intermediate layer being substantially free of gallium, said at least one layer being situated over said substrate;
a transition layer comprising a superlattice, said transition layer not consisting entirely of said superlattice;
a gallium nitride layer formed over said transition layer.
12. The semiconductor structure of claim 11 wherein said at least one layer comprises an aluminum nitride alloy.
13. The semiconductor structure of claim 11 wherein said at least one compositionally-graded layer is graded discontinuously across the thickness of the layer.
14. The semiconductor structure of claim 11 wherein said transition layer comprises an alloy of gallium nitride selected from the group consisting of Al X In Y Ga (1-X-Y) N, In Y Ga (1-Y) N, and Al X Ga (1-X) N.
15. The semiconductor structure of claim 14 wherein a concentration of gallium in said transition layer is graded.
16. The semiconductor structure of claim 11 wherein said substrate comprises a silicon-on-insulator (SOI) substrate.
17. The semiconductor structure of claim 11 wherein said substrate comprises a silicon-on-sapphire (SOS) substrate.
18. The semiconductor structure of claim 11 wherein said substrate comprises a SIMOX substrate.
19. A semiconductor structure comprising:
a substrate;
a substantially gallium free intermediate layer comprising first and second aluminum nitride layers formed over at least one layer, said at least one layer being situated over said substrate;
a transition layer comprising a superlattice, said transition layer not consisting entirely of said superlattice;
a gallium nitride layer formed over said transition layer.
20. The semiconductor structure of claim 19 wherein said first aluminum nitride layer is formed at a first temperature, and said second aluminum nitride layer is formed at a second temperature different from said first temperature.