Microcavity light emitting diode method of manufacture
View Patent ↗A high efficiency microcavity light emitting diode comprises a stack of Al x In y Ga 1-x-y N layers, where 0≦x, y, x+y≦1, with each layer having a high crystalline quality. The stack has a uniform thickness less than 6λ/n, with an active layer centered approximately (2i+1)λ/(4n) from a reflective electrical contact, where λ is the peak emission wavelength, n is the index of refraction at the peak emission wavelength, i is an integer, and each layer within the stack has a dislocation density below about 10 5 cm −2 .
1. A microcavity light emitting diode, comprising:
a semiconductor active layer comprising Al w In x Ga 1-w-x N, where 0≦w, x, w+x≦1, the semiconductor active layer being characterized by a peak emission wavelength (λ) and having an active layer surface dislocation density below about 10 5 cm −2 ;
at least one semiconductor n-type layer comprising Al u In v Ga 1-u-v N, where 0≦u, v, u+v≦1, the at least one semiconductor n-type layer having an n-type layer surface dislocation density below about 10 5 cm −2 ;
at least one semiconductor p-type layer comprising Al q In r Ga 1-q-r N, where 0≦q, r, q+r≦1;
an electrical contact coupled to the at least one semiconductor n-type layer;
a reflective electrical contact coupled to the at least one semiconductor p-type layer and the at least one semiconductor n-type layer, the reflective electrical contact having a reflectivity greater than about 70% at the peak emission wavelength;
a total thickness characterizing the semiconductor active layer, the at least one semiconductor n-type layer, and the at least one semiconductor p-type layer of less than 6λ/n; and
a uniformity to within approximately ±λ/(4n) wherein n is a thickness averaged index of refraction at the peak emission wavelength characterizing the total thickness of the semiconductor active layer, the at least one semiconductor n-type layer, and the at least one semiconductor p-type layer.
2. The microcavity light emitting diode of claim 1 , wherein the total thickness is less than 3λ/n.
3. The microcavity light emitting diode of claim 1 , wherein the at least one semiconductor p-type layer has a p-type layer surface dislocation density below about 10 5 cm −2 .
4. The microcavity light emitting diode of claim 1 , wherein each of the active layer surface dislocation density, the n-type layer surface dislocation density, and a p-type layer surface dislocation density of the at least one semiconductor p-type layer are below 10 4 cm −2 .
5. The microcavity light emitting diode of claim 4 , wherein each of the active layer surface dislocation density, the n-type layer surface dislocation density, and the p-type layer surface dislocation density are below 10 3 cm −2 .
6. The microcavity light emitting diode of claim 5 , wherein each of the active layer surface dislocation density, the n-type layer surface dislocation density, and the p-type layer surface dislocation density are below 10 2 cm −2 .
7. The microcavity light emitting diode of claim 1 , wherein the semiconductor active layer is centered at a distance within ±λ/(8n) of (2i+1)λ/(4n), where i is an integer, from the reflective electrical contact.
8. The microcavity light emitting diode of claim 1 , wherein the semiconductor active layer has an overall thickness of less than λ/(4n).
9. The microcavity light emitting diode of claim 1 , wherein the total thickness is uniformly within ±λ/(4n) of jλ/(2n), where j is an integer.
10. The microcavity light emitting diode of claim 1 , wherein the total thickness is uniform to within ±λ/(8n).
11. The microcavity light emitting diode of claim 1 , wherein the reflectivity of the reflective electrical contact is greater than about 90%.
12. The microcavity light emitting diode of claim 1 , wherein the semiconductor active layer has an active layer surface orientation within 5 degrees of {1 −1 0 0}, the at least one semiconductor n-type layer has an n-type surface orientation within 5 degrees of {1 −1 0 0}, and the at least one semiconductor p-type layer has a p-type surface orientation within 5 degrees of {1 −1 0 0}.
13. The microcavity light emitting diode of claim 1 , the semiconductor active layer has an active layer surface orientation within 5 degrees of {1 1 −2 0}, the at least one semiconductor n-type layer has an n-type surface orientation within 5 degrees of {1 1 −2 0}, and the at least one semiconductor p-type layer has a p-type surface orientation within 5 degrees of {1 1 −2 0}.
14. The microcavity light emitting diode of claim 1 , the semiconductor active layer has an active layer surface orientation within 5 degrees of {1 −1 0 ±1}, the at least one semiconductor n-type layer has an n-type surface orientation within 5 degrees of {1 −1 0 ±1}, and the at least one semiconductor p-type layer has a p-type surface orientation within 5 degrees of {1 −1 0 ±1}.
15. The microcavity light emitting diode of claim 1 , the semiconductor active layer has an active layer surface orientation within 5 degrees of {1 −1 0 ±2}, the at least one semiconductor n-type layer has an n-type surface orientation within 5 degrees of {1 −1 0 ±2}, and the at least one semiconductor p-type layer has a p-type surface orientation within 5 degrees of {1 −1 0 ±2}.
16. The microcavity light emitting diode of claim 1 , the semiconductor active layer has an active layer surface orientation within 5 degrees of {1 −1 0 ±3}, the at least one semiconductor n-type layer has an n-type surface orientation within 5 degrees of {1 −1 0 ±3}, and the at least one semiconductor p-type layer has a p-type surface orientation within 5 degrees of {1 −1 0 ±3}.
17. The microcavity light emitting diode of claim 1 , the semiconductor active layer has an active layer surface orientation within 5 degrees of {1 1 −2 ±2}, the at least one semiconductor n-type layer has an n-type surface orientation within 5 degrees of {1 1 −2 ±2}, and the at least one semiconductor p-type layer has a p-type surface orientation within 5 degrees of {1 1 −2 ±2}.
18. The microcavity light emitting diode of claim 1 , the semiconductor active layer has an active layer surface orientation within 5 degrees of {2 0 −2 ±1}, the at least one semiconductor n-type layer has an n-type surface orientation within 5 degrees of {2 0 −2 ±1}, and the at least one semiconductor p-type layer has a p-type surface orientation within 5 degrees of {2 0 −2 ±1}.
19. The microcavity light emitting diode of claim 1 , the semiconductor active layer has an active layer surface orientation within 5 degrees of (0 0 0 1), the at least one semiconductor n-type layer has an n-type surface orientation within 5 degrees of (0 0 0 1), and the at least one semiconductor p-type layer has a p-type surface orientation within 5 degrees of (0 0 0 1).
20. The microcavity light emitting diode of claim 1 , the semiconductor active layer has an active layer surface orientation within 5 degrees of (0 0 0 −1), the at least one semiconductor n-type layer has an n-type surface orientation within 5 degrees of (0 0 0 −1), and the at least one semiconductor p-type layer has a p-type surface orientation within 5 degrees of (0 0 0 −1).
21. The microcavity light emitting diode of claim 1 , further comprising a tunnel junction.
22. The microcavity light emitting diode of claim 1 , wherein the at least one semiconductor p-type layer and the reflective electrical contact are substantially parallel in configuration.
23. The microcavity light emitting diode of claim 1 , wherein the at least one semiconductor p-type layer, the reflective electrical contact, and the one semiconductor n-type layer are in parallel configuration.
24. The microcavity light emitting diode of claim 1 further comprising a light extraction efficiency of greater than about 50%.
25. The microcavity light emitting diode of claim 1 further comprising a drive current of greater than about 100 milliamperes per square millimeter.
26. The microcavity light emitting diode of claim 1 wherein the thickness averaged index of refraction (n) is between about 2.2 and about 2.8.