AllnGaP 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 method comprising:
providing a crystalline growth layer over a first substrate, the growth layer having a lattice constant greater than the lattice constant of GaAs; and
growing light emitting diode (LED) layers overlying the growth layer, the LED layers comprising a first (Al x Ga 1-x ) 1-y In y P epitaxial layer of a first conductivity type, a second epitaxial layer of a second conductivity type, and an active layer disposed between the first and second epitaxial layers, the active layer comprising one or more layers of material comprising any combination of Al, Ga, In, and P, wherein 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.
2. The method of claim 1 wherein 0≦x≦1.0, and y>0.48.
3. The method of claim 1 wherein forming a crystalline growth layer comprises forming a graded InGaAs layer on a GaAs substrate while increasing the amount of indium until a desired lattice constant, greater than the lattice constant of GaAs, is obtained.
4. The method of claim 1 wherein forming a crystalline growth layer comprises forming a graded InGaP layer on a GaAs substrate while increasing the amount of indium until a desired lattice constant, greater than the lattice constant of GaAs, is obtained.
5. The method of claim 1 wherein forming a crystalline growth layer comprises:
growing an epitaxial layer comprising InGaP, InGaAs, or AlInGaP over a GaAs substrate, where the epitaxial layer is strained when overlying the GaAs;
implanting hydrogen into the GaAs substrate to act as a delamination layer;
bonding the epitaxial layer to the first substrate;
heating the GaAs substrate so that the hydrogen causes the epitaxial layer to delaminate from the GaAs substrate, whereby the strained epitaxial layer relaxes to expand its lattice constant when released from the GaAs substrate, the relaxed epitaxial layer comprising the growth layer.
6. The method of claim 5 further comprising:
forming a bonding layer over the first substrate;
wherein bonding the epitaxial layer to the first substrate comprises bonding the epitaxial layer to the bonding layer.
7. The method 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.
8. The method of claim 1 wherein the first epitaxial layer is an AlInP confining layer, and the second epitaxial layer is an AlInP confining layer.
9. The method of claim 1 further comprising forming a reflective material overlying the second epitaxial layer.
10. The method of claim 1 wherein the first substrate is a GaAs substrate, and wherein the growth layer is an InGaP layer epitaxially grown over the GaAs substrate.
11. The method of claim 1 wherein the first substrate is a GaAs substrate, and wherein the growth layer is an AlInGaP layer epitaxially grown over the GaAs substrate.
12. The method of claim 1 wherein the first substrate is a GaAs substrate, and wherein the growth layer is an InGaAs layer epitaxially grown over the GaAs substrate.
13. The method of claim 1 wherein y equals approximately 0.53.
14. The method of claim 1 wherein the lattice constant of the active layer is greater than 5.66 Å.
15. The method of claim 1 wherein the lattice constant of the active layer is between 5.66 Å and 5.73 Å.
16. The method of claim 1 wherein the growth layer comprises an In x Ga 1-x As epitaxial layer, where 0<x<0.18.
17. The method of claim 1 wherein the growth layer comprises an In y Ga 1-y P epitaxial layer, where 0.48<y<0.66.
18. The method of claim 1 further comprising growing at least one intervening epitaxial layer between the first epitaxial layer and the active layer.
19. The method of claim 1 further comprising growing at least one intervening epitaxial layer between the active layer and the second epitaxial layer.
20. The method of claim 1 further comprising removing the growth layer and first substrate, leaving a remaining structure.
21. The method of claim 20 further comprising bonding a transparent substrate to the remaining structure.
22. The method of claim 1 further comprising:
providing a reflective layer facing a surface of the active layer; and
removing the growth layer and first substrate.
23. The method of claim 1 further comprising forming a window layer over a surface of the active layer.
24. The method of claim 1 further comprising:
forming electrical contacts on a same side of the active layer to form a flip chip LED device; and
removing the growth layer and first substrate.
25. The method of claim 1 wherein the first substrate is transparent.