Light-emitting device having element(s) for increasing the effective carrier capture cross-section of quantum wells
View Patent ↗Light-emitting devices are described. One example of a light-emitting device includes a first barrier layer and a second barrier layer, and a quantum well layer located between the first and second barrier layers. The first and second barrier layers are composed of gallium arsenide, and the quantum well layer is composed of indium gallium arsenide nitride. A first layer is located between the quantum well layer and the first barrier layer. The first layer has a bandgap energy between that of the first barrier layer and that of the quantum well layer. Another example of a light-emitting device includes a quantum well and a carrier capture element adjacent the quantum well. The carrier capture element increases the effective carrier capture cross-section of the quantum well.
1. A light-emitting device, comprising:
a first barrier layer and a second barrier layer, said first and second barrier layers comprising gallium arsenide (GaAs);
a quantum well layer sandwiched between said first and second barrier layers, said quantum well layer comprising indium gallium arsenide nitride (InGaAsN); and
sandwiched between said quantum well layer and said first barrier layer, a first layer of a material comprising GaAs and another element, wherein said material of said first layer has a bandgap energy between the bandgap energies of said first barrier layer and said quantum well layer and wherein a fraction of said another element is graded, said fraction increasing toward said quantum well layer.
2. The light-emitting device of claim 1 wherein said other element is nitrogen and wherein said fraction increases from zero percent at said first barrier layer to approximately one percent at said quantum well layer.
3. The light-emitting device of claim 1 wherein said other element is indium and wherein said fraction increases from zero percent at said first barrier layer to approximately 10-20 percent at said quantum well layer.
4. The light-emitting device of claim 1 further comprising a second layer sandwiched between said quantum well layer and said second barrier layer, said second layer comprising GaAs and another element, wherein said second layer has a bandgap energy between the bandgap energies of said second barrier layer and said quantum well layer.
5. The light-emitting device of claim 1 further comprising a carrier capture element cooperatively disposed relative to said quantum well layer, said carrier capture element in combination with said quantum well layer capturing more carriers than would be captured by said quantum well layer alone.
6. The light-emitting device of claim 5 wherein said carrier capture element comprises an auxiliary quantum well layer proximate to said quantum well layer, wherein said auxiliary quantum well layer has a ground state energy substantially aligned with a non-ground energy state of said quantum well layer to provide resonant tunneling of carriers from said auxiliary quantum well layer to said quantum well layer.
7. The light-emitting device of claim 5 wherein said carrier capture element comprises a carrier reflector proximate to said quantum well layer, said carrier reflector for reflecting carriers not captured by said quantum well layer back toward said quantum well layer.
8. The light-emitting device of claim 1 comprising a vertical-cavity surface-emitting laser (VCSEL) for generating optical signals having a wavelength of approximately 1200 nanometers or more.
9. A light-emitting device, comprising:
a quantum well structure defining a quantum well; and
a carrier capture element located adjacent said quantum well to increase the effective carrier capture cross-section of said quantum well, wherein said carrier capture element comprises a first auxiliary quantum well, wherein said first auxiliary quantum well has a ground state energy substantially aligned with a non-ground energy state of said quantum well to provide resonant tunneling of carriers from said first auxiliary quantum well to said quantum well.
10. The light-emitting device of claim 9 further comprising a second auxiliary quantum well located on the opposite side of said quantum well from said first auxiliary quantum well, wherein said second auxiliary quantum well has a ground state energy substantially aligned with a non-ground energy state of said quantum well to provide resonant tunneling of carriers from said second auxiliary quantum well to said quantum well.
11. The light-emitting device of claim 9 further comprising a second auxiliary quantum well located on the same side of said quantum as said first auxiliary quantum well, wherein said second auxiliary quantum well has a ground state energy substantially aligned with a non-ground energy state of said first auxiliary quantum well to provide resonant tunneling of carriers from said second auxiliary quantum well to said first auxiliary quantum well.
12. The light-emitting device of claim 11 wherein at least one of said first and second auxiliary quantum wells comprises gallium arsenide nitride (GaAsN).
13. The light-emitting device of claim 12 wherein a fraction of nitrogen is graded, said fraction increasing toward said quantum well.
14. The light-emitting device of claim 11 wherein at least one of said first and second auxiliary quantum wells comprises indium gallium arsenide (InGaAs).
15. The light-emitting device of claim 14 wherein a fraction of indium is graded, said fraction increasing toward said quantum well.
16. The light-emitting device of claim 9 further comprising a carrier reflector, said carrier reflector for reflecting carriers not captured by said quantum well back toward said quantum well.
17. The light-emitting device of claim 16 wherein said carrier reflector and said quantum well are separated by a distance sufficient to prevent tunneling from said quantum well to said reflector.
18. The light-emitting device of claim 16 wherein said carrier reflector is sized to maintain coherence of carriers across said reflector.
19. The light-emitting device of claim 16 wherein said carrier reflector comprises alternating layers of gallium arsenide nitride (GaAsN) and gallium arsenide (GaAs).
20. The light-emitting device of claim 19 wherein a layer of GaAsN is approximately two nanometers thick and a layer of GaAs is approximately three nanometers thick.
21. The light-emitting device of claim 16 wherein said carrier reflector provides a barrier height in excess of about 300 millielectron volts (meV).
22. The light-emitting device of claim 9 wherein said quantum well structure comprises a quantum well layer comprising indium gallium arsenide nitride (InGaAsN) sandwiched between a first barrier layer and a second barrier layer, said first and second barrier layers comprising gallium arsenide (GaAs).
23. The light-emitting device of claim 22 further comprising a layer disposed between said quantum well layer and said first barrier layer, said layer comprising GaAs and another element.
24. The light-emitting device of claim 23 wherein a fraction of said element is uniform within said layer.
25. The light-emitting device of claim 23 wherein a fraction of said element is graded, said fraction increasing toward said quantum well layer.
26. The light-emitting device of claim 23 wherein said element is nitrogen or indium.
27. The light-emitting device of claim 9 comprising a vertical-cavity surface-emitting laser (VCSEL).
28. A light-emitting device, comprising:
a first barrier layer and a second barrier layer;
a quantum well layer sandwiched between said first and second barrier layers;
sandwiched between said quantum well layer and said first barrier layer, a first layer of a material having a bandgap energy between the bandgap energies of said first barrier layer and said quantum well layer, wherein said first layer comprises the same elements as said first and second barrier layers plus nitrogen; and
a carrier capture element located adjacent said quantum well layer to increase the effective carrier capture cross-section of said quantum well layer.
29. The light-emitting device of claim 28 wherein a fraction of said nitrogen is graded, said fraction increasing toward said quantum well layer.
30. The light-emitting device of claim 28 wherein a fraction of said nitrogen is uniform within said first layer.
31. The light-emitting device of claim 28 wherein said carrier capture element comprises an auxiliary quantum well layer proximate to said quantum well layer, wherein said auxiliary quantum well layer has a ground state energy substantially aligned with a non-ground energy state of said quantum well layer to provide resonant tunneling of carriers from said auxiliary quantum well layer to said quantum well layer.
32. The light-emitting device of claim 28 wherein said carrier capture element comprises a carrier reflector proximate to said quantum well layer, said carrier reflector for reflecting carriers not captured by said quantum well layer back toward said quantum well layer.
33. The light-emitting device of claim 28 wherein said first and second barrier layers comprise gallium arsenide (GaAs), said quantum well layer comprises indium gallium arsenide nitride (InGaAsN), and said first barrier layer comprises gallium arsenide nitride (GaAsN).
34. A light-emitting device, comprising:
a quantum well structure defining a quantum well; and
a carrier capture element located adjacent said quantum well to increase the effective carrier capture cross-section of said quantum well, wherein said carrier capture element comprises a carrier reflector, said carrier reflector for reflecting carriers not captured by said quantum well back toward said quantum well.
35. The light-emitting device of claim 34 wherein said carrier reflector and said quantum well are separated by a distance sufficient to prevent tunneling from said quantum well to said reflector.
36. The light-emitting device of claim 34 wherein said carrier reflector is sized to maintain coherence of carriers across said reflector.
37. The light-emitting device of claim 34 wherein said carrier reflector comprises alternating layers of gallium arsenide nitride (GaAsN) and gallium arsenide (GaAs).
38. The light-emitting device of claim 37 wherein a layer of GaAsN is approximately two nanometers thick and a layer of GaAs is approximately three nanometers thick.
39. The light-emitting device of claim 34 wherein said carrier reflector provides a barrier height in excess of about 300 millielectron volts (meV).