The present invention relates to light emitting diodes comprising at least one nanowire. The LED according to the invention is an upstanding nanostructure with the nanowire protruding from a substrate. A bulb with a larger diameter than the nanowire is arranged in connection to the nanowire and at an elevated position with regards to the substrate. A pn-junction is formed by the combination of the bulb and the nanowire resulting in an active region to produce light.
1. An upstanding nanostructured LED comprising:
a substrate and a nanowire protruding from the substrate, wherein a bulb is arranged in connection with the nanowire and at an elevated position with regards to the substrate, the bulb having a larger diameter than the nanowire, the bulb comprising an active region to produce light and the bulb having bulk properties;
a mask layer located over the substrate and surrounding a portion of the nanowire not covered by the bulb, wherein the mask layer comprises a silicon nitride mask layer;
a spacer layer located over the silicon nitride mask layer and below the bulb, the spacer layer surrounding a portion of the nanowire not covered by the bulb; and
wherein a p-n junction is present at an interface between the bulb and the nanowire above the spacer layer.
2. The LED of claim 1 , wherein the bulb has a cylindrical shape.
3. The LED of claim 2 , wherein the nanowire comprises a n-GaN core, the active region comprises InGaN well layers, and the bulb further comprises a p-GaN shell.
4. The LED of claim 3 , wherein the mask layer comprises a silicon nitride mask layer located on a GaN buffer layer.
5. The LED of claim 1 , further comprising a reflective structure in the nanowire.
6. The LED of claim 5 , wherein the reflective structure comprises a multilayered structure.
7. The LED of claim 1 , wherein the nanowire comprises a n-GaN core, the active region comprises InGaN well layers, and the bulb further comprises a p-GaN shell.
8. The LED of claim 7 , wherein the mask layer is located on a GaN buffer layer.
9. The LED of claim 1 , wherein a combined thickness of the mask layer and the spacer layer is equal to or greater than a quarter wavelength of the light emitted by the LED.
10. The LED of claim 9 , wherein the bulb covers more than one half of an entire length of the nanowire.
11. The LED of claim 9 , wherein:
the nanowire has a first material composition; and
the bulb has a second material composition that is different from the first material composition.
12. The LED of claim 9 , further comprising a top contact that is in physical contact with a surface of the bulb.
13. The LED of claim 12 , wherein the top contact comprises a reflective material and functions both as an electrical contact and a reflector.
14. The LED of claim 9 , further comprising:
a resistive material portion that is in physical contact with a surface of the bulb; and
a top contact that is in physical contact with the resistive material portion.
15. The LED of claim 9 , wherein the nanowire and the bulb are configured to provide a point like emission center within a middle portion of the bulb.