Light emitting devices having dislocation density maintaining buffer layers
View Patent ↗A method for forming a light emitting device comprises forming a buffer layer having a plurality of layers comprising a substrate, an aluminum gallium nitride layer adjacent to the substrate, and a gallium nitride layer adjacent to the aluminum gallium nitride layer. During the formation of each of the plurality of layers, one or more process parameters are selected such that an individual layer of the plurality of layers is strained.
1. A method for forming a light emitting device, comprising:
forming a buffer layer on a substrate at a growth temperature, the buffer layer comprising an aluminum gallium nitride (AlGaN) layer and a gallium nitride (GaN) layer, wherein, at the growth temperature, a tensile strain is generated in the buffer layer; and
forming a light emitting stack on the buffer layer, the light emitting stack including an active layer configured to generate light upon the recombination of electrons and holes,
wherein at least one layer of the light emitting stack and the buffer layer has a first coefficient of thermal expansion higher than a second coefficient of thermal expansion of the substrate, and
a growth condition for forming the buffer layer is selected to generate a compressive strain in the buffer layer during cool-down to a room temperature to counterbalance the tensile strain generated between the buffer layer and the substrate so that the light emitting device has a radius of curvature (absolute value) that is greater than 50 m.
2. The method of claim 1 , wherein the growth condition for forming the buffer layer is selected to form the buffer layer so as to have a defect density between 1×10 8 cm −2 and 2×10 10 cm −2 .
3. The method of claim 1 , wherein, during the cool-down to the room temperature, the substrate contracts at a lower rate than the buffer layer.
4. The method of claim 1 , wherein the substrate is a silicon substrate.
5. The method of claim 1 , wherein the buffer layer further comprises an aluminum nitride (AlN) layer formed between the AlGaN layer and the substrate.
6. The method of claim 5 , wherein the GaN layer is formed between the AlGaN layer and the light emitting stack.
7. The method of claim 1 , wherein the combined thickness of the buffer layer and the light emitting stack is less than or equal to 5 μm.
8. The method of claim 1 , wherein the combined thickness of the buffer layer and the light emitting stack is less than or equal to 3 μm.
9. A method for forming a light emitting device, comprising:
forming a buffer layer on a substrate at a growth temperature, the buffer layer comprising an aluminum gallium nitride (AlGaN) layer and a gallium nitride (GaN) layer, wherein, at the growth temperature, a tensile strain is generated in the buffer layer; and
forming a light emitting stack on the buffer layer, the light emitting stack including an active layer configured to generate light upon the recombination of electrons and holes,
wherein at least one layer of the light emitting stack and the buffer layer has a first coefficient of thermal expansion higher than a second coefficient of thermal expansion of the substrate, and
a growth condition for forming the buffer layer is selected to generate a compressive strain in the buffer layer during cool-down to a room temperature to counterbalance the tensile strain generated between the buffer layer and the substrate.
10. The method of claim 9 , wherein the growth condition for forming the buffer layer is selected to form the buffer layer so as to have a defect density between 1×10 8 cm −2 and 2×10 10 cm −2 .
11. The method of claim 9 , wherein, during the cool-down to the room temperature, the substrate contracts at a lower rate than the buffer layer.
12. The method of claim 9 , wherein the substrate is a silicon substrate.
13. The method of claim 9 , wherein the buffer layer further comprises an aluminum nitride (AlN) layer formed between the AlGaN layer and the substrate.
14. The method of claim 13 , wherein the GaN layer is formed between the AlGaN layer and the light emitting stack.
15. The method of claim 9 , wherein the combined thickness of the buffer layer and the light emitting stack is less than or equal to 5 μm.
16. The method of claim 9 , wherein the combined thickness of the buffer layer and the light emitting stack is less than or equal to 3 μm.
17. A method for forming a light emitting device, comprising:
forming an AlN layer on a substrate at a first growth temperature, wherein, at the first growth temperature, a tensile strain is generated in the AlN layer;
forming a first Al x Ga 1-x N layer on the AlN layer at a second growth temperature, wherein ‘x’ is a number between 0 and 1, and, at the second growth temperature, a compressive strain is generated in the first Al x Ga 1-x N layer;
forming a GaN layer on the first Al x Ga 1-x N layer at a third growth temperature, wherein, at the third growth temperature, a compressive strain is generated in the GaN layer; and
forming a light emitting stack on the GaN layer, the light emitting stack having an n-type gallium nitride (n-GaN) layer, a p-type gallium nitride (p-GaN) layer, and an active layer between the n-GaN and p-GaN layers,
wherein the AlN layer, the first Al x Ga 1-x N layer and the GaN layer forms a buffer layer,
at least one layer of the light emitting stack and the buffer layer has a first coefficient of thermal expansion higher than a second coefficient of thermal expansion of the substrate, and
a growth condition for forming the buffer layer is selected to generate a compressive strain in the buffer layer during cool-down to a room temperature to balance the strain generated between the buffer layer and the substrate.
18. The method of claim 17 , wherein the growth condition for forming the buffer layer is selected to generate the compressive strain in the buffer layer during the cool-down to the room temperature to balance the strain generated between the buffer layer and the substrate so that the light emitting device has a radius of curvature (absolute value) that is greater than 50 m.
19. The method of claim 17 , wherein, during the cool-down to the room temperature, the substrate contracts at a lower rate than the buffer layer.
20. The method of claim 17 , wherein the growth condition for forming the buffer layer is selected to form the buffer layer so as to have a defect density between 1×10 8 cm −2 and 2×10 10 cm −2 .
21. The method of claim 17 , wherein, during the cool-down to the room temperature, the substrate contracts at a lower rate than the light emitting stack.
22. The method of claim 17 , wherein the substrate is a silicon substrate.
23. The method of claim 17 , wherein the combined thickness of the buffer layer and the light emitting stack is less than or equal to 5 μm.
24. The method of claim 17 , wherein the combined thickness of the buffer layer and the light emitting stack is less than or equal to 3 μm.
25. The method of claim 17 , further comprising forming a second Al y Ga 1-y N layer on the first Al x Ga1-xN layer, wherein ‘y’ is a number between 0 and 1.