Light emitting device with improved extraction efficiency
In embodiments of the invention, a semiconductor structure comprising a III-nitride light emitting layer disposed between an n-type region and a p-type region is grown on a substrate. The substrate is a non-III-nitride material. The substrate has an in-plane lattice constant a substrate . At least one III-nitride layer in the semiconductor structure has a bulk lattice constant a layer and [(|a substrate −a layer |)/a substrate ]100% is no more than 1%. A surface of the substrate opposite the surface on which the semiconductor structure is grown is textured.
1. A device comprising:
a substrate; and
a semiconductor structure grown on the substrate, the semiconductor structure comprising a III-nitride light emitting layer disposed between an InGaN n-type region and a p-type region;
wherein:
the substrate is a non-III-nitride material;
the substrate has an in-plane lattice constant a substrate ;
at least one III-nitride layer in the semiconductor structure has a bulk lattice constant a layer ;
[(|a substrate −a layer |)/a substrate ]*100% is no more than 1%; and
a surface of the substrate opposite a surface on which the semiconductor structure is grown is textured.
2. The device of claim 1 wherein the substrate is ScMgAlO 4 .
3. The device of claim 1 wherein the substrate is RAO 3 (MO) n , where R is selected from Sc, In, Y, and the lanthanides; A is selected from Fe (III), Ga, and Al; M is selected from Mg, Mn, Fe (II), Co, Cu, Zn and Cd; and n is an integer ≧1.
4. The device of claim 1 wherein the substrate has an index of refraction of at least 2.0.
5. The device of claim 1 wherein a surface of the substrate on which the semiconductor structure is grown is textured.
6. The device of claim 1 further comprising a lattice of holes or posts formed on a surface of the substrate on which the semiconductor structure is grown.
7. The device of claim 1 wherein the substrate is shaped into a truncated inverted pyramid.
8. The device of claim 1 further comprising a photonic crystal formed in one of a surface of the substrate on which the semiconductor structure is grown and a semiconductor layer in the semiconductor structure.
9. The device of claim 8 wherein the photonic crystal is positioned within 2 μm of the III-nitride light emitting layer.
10. The device of claim 1 wherein the surface of the substrate opposite the surface on which the semiconductor structure is grown is textured with hexagonal pyramids.
11. The device of claim 1 wherein the semiconductor structure is attached to a mount and the substrate is less than 50 μm thick.
12. A method comprising:
growing on a substrate a semiconductor structure comprising an InGaN light emitting layer disposed between an InGaN n-type region and an InGaN p-type region; and
removing the substrate by one of wet etching and a mechanical method;
wherein:
the substrate is a non-III-nitride material;
the substrate has an in-plane lattice constant a substrate ;
at least one III-nitride layer in the semiconductor structure has a bulk lattice constant a layer ;
[(|a substrate −a layer |)/a substrate ]*100% is no more than 1%; and
a thickness of the semiconductor structure is selected to reduce a number of guided optical modes within the semiconductor structure.
13. The method of claim 12 further comprising after removing the substrate, depositing a conductive material on the exposed surface of the semiconductor structure.
14. The method of claim 13 wherein the conductive material is a transparent oxide.
15. The method of claim 12 wherein the thickness of the semiconductor structure is between 200 nm and 2 μm.
16. A method comprising:
providing a substrate with a patterned surface, wherein the patterned surface comprises at least one region of lower elevation where a portion of the substrate is removed;
growing on the patterned surface a semiconductor structure comprising an InGaN layer in direct contact with the substrate, and a III-nitride light emitting layer disposed between an n-type region and a p-type region, wherein semiconductor material fills in the region of lower elevation; and
removing the substrate with an etch that removes the substrate without attacking the semiconductor material such that the semiconductor material filling in the region of lower elevation remains part of the semiconductor structure;
wherein:
the substrate is a non-III-nitride material;
the substrate has an in-plane lattice constant a substrate ;
at least one III-nitride layer in the semiconductor structure has a bulk lattice constant a layer ; and
[(|a substrate −a layer |)/a substrate ]*100% is no more than 1%.
17. The method of claim 16 wherein the patterned surface comprises a plurality of posts formed on the substrate surface, and the at least one region of lower elevation comprises a region between two posts.
18. The device of claim 1 further comprising a metal n-contact disposed on the n-type region and a metal p-contact disposed on the p-type region, wherein the n-contact is disposed on a surface of the n-type region exposed by etching a via through the substrate and wherein the n- and p-contacts are formed on opposite sides of the semiconductor structure.