A1InGaP LED having reduced temperature dependence
View Patent ↗To increase the lattice constant of AlInGaP LED layers to greater than the lattice constant of GaAs for reduced temperature sensitivity, an engineered growth layer is formed over a substrate, where the growth layer has a lattice constant equal to or approximately equal to that of the desired AlInGaP layers. In one embodiment, a graded InGaAs or InGaP layer is grown over a GaAs substrate. The amount of indium is increased during growth of the layer such that the final lattice constant is equal to that of the desired AlInGaP active layer. In another embodiment, a very thin InGaP, InGaAs, or AlInGaP layer is grown on a GaAs substrate, where the InGaP, InGaAs, or AlInGaP layer is strained (compressed). The InGaP, InGaAs, or AlInGaP thin layer is then delaminated from the GaAs and relaxed, causing the lattice constant of the thin layer to increase to the lattice constant of the desired overlying AlInGaP LED layers. The LED layers are then grown over the thin InGaP, InGaAs, or AlInGaP layer.
1. A light emitting device comprising:
a light emitting diode (LED) portion comprising:
a first (Al x Ga 1−x ) 1−y In y P epitaxial layer of a first conductivity type formed on a growth layer, the growth layer having a lattice constant greater than that of GaAs;
an active layer epitaxially grown over the first (Al x Ga 1−x ) 1−y In y P epitaxial layer, wherein the active layer comprises one or more layers of material comprising any combination of Al, Ga, In, and P, such that the active layer has a lattice constant greater than the lattice constant of GaAs and approximately equal to the lattice constant of the growth layer, and wherein the active layer emits visible light; and
a second epitaxial layer of a second conductivity type grown over the active layer.
2. The device of claim 1 wherein 0≦x≦1.0, and y>0.48.
3. The device of claim 1 wherein the growth layer comprises an epitaxial layer formed on a graded InGaAs layer.
4. The device of claim 1 wherein the growth layer comprises an epitaxial layer formed on a graded InGaP layer.
5. The device of claim 1 wherein the growth layer comprises an epitaxial layer of InGaP or InGaAs grown over a GaAs substrate, where the InGaP or InGaAs layer was strained when overlying the GaAs substrate then relaxed to expand its lattice constant when released from the GaAs substrate.
6. The device of claim 1 wherein the active layer is not strained.
7. The device of claim 1 wherein the active layer is strained.
8. The device of claim 1 wherein the first epitaxial layer is an n-type confining layer, and the second epitaxial layer is a p-type confining layer.
9. The device of claim 1 wherein the first epitaxial layer is an AlInP confining layer, and the second epitaxial layer is an AlInP confining layer.
10. The device of claim 1 further comprising a reflective material overlying the second epitaxial layer.
11. The device of claim 1 further comprising a transparent window layer overlying the second epitaxial layer.
12. The device of claim 1 wherein the growth layer is an InGaP layer epitaxially grown over a GaAs substrate.
13. The device of claim 1 wherein the growth layer is an InGaAs layer epitaxially grown over a GaAs substrate.
14. The device of claim 1 wherein the device further comprises the growth layer.
15. The device of claim 1 wherein y equals approximately 0.53.
16. The device of claim 1 wherein the lattice constant of the active layer is greater than 5.66 Å.
17. The device of claim 1 wherein the lattice constant of the active layer is between 5.66 Å and 5.73 Å.
18. The device of claim 1 wherein the visible light is red light.
19. The device of claim 1 wherein the visible light is yellow light.
20. The device of claim 1 wherein the visible light is green light.
21. The device of claim 1 wherein the growth layer comprises an In x Ga 1−x As epitaxial layer, where 0<x<0.18.
22. The device of claim 1 wherein the growth layer comprises an In y Ga 1−y P epitaxial layer, where 0.48<y<0.66.
23. The device of claim 1 further comprising at least one intervening epitaxial layer between the first epitaxial layer and the active layer.
24. The device of claim 1 further comprising at least one intervening epitaxial layer between the active layer and the second epitaxial layer.
25. The device of claim 1 wherein the active layer has a first surface and an opposing second surface, the device further comprising a window layer formed opposing the first surface of the active layer and a bonded substrate opposing the second surface of the active layer.
26. The device of claim 1 further comprising:
a substrate; and
a reflector between the substrate and the active layer.
27. The device of claim 1 further comprising at least one reflector opposing at least one surface of the active layer.