Reduction of surface recombination losses in micro-LEDs
Disclosed herein are systems and methods for reducing surface recombination losses in micro-LEDs. In some embodiments, a method of forming an LED involves forming a semiconductor structure on a substrate. The semiconductor structure includes a p-side semiconductor layer, an n-side semiconductor layer, and an active light emitting layer between the p-side semiconductor layer and the n-side semiconductor layer. The semiconductor structure is also formed to include a light outcoupling surface facing the substrate. The light outcoupling surface has a diameter less than twice an electron diffusion length of a material of the semiconductor structure. The method further involves implanting ions in an outer region of the semiconductor structure, then annealing the outer region after the ions have been implanted. The annealing causes the ions to intermix with atoms within the outer region, thereby increasing a bandgap of the outer region.
1. A method of forming a light-emitting diode, comprising:
forming a semiconductor structure on a substrate, wherein the semiconductor structure comprises a p-side semiconductor layer, an n-side semiconductor layer, an active light emitting layer between the p-side semiconductor layer and the n-side semiconductor layer, and a light outcoupling surface facing the substrate;
implanting ions in an outer region of the semiconductor structure; and
annealing the outer region after the ions have been implanted, wherein:
the annealing causes the ions to intermix with atoms within the outer region, thereby increasing a bandgap of the outer region, and
the light outcoupling surface has a diameter less than twice an electron diffusion length of a material of the semiconductor structure.
2. The method of claim 1 , further comprising:
forming a p contact over the p-side semiconductor layer prior to implanting the ions, wherein the p contact defines an approximate boundary between the outer region and a central region of the semiconductor structure.
3. The method of claim 1 , further comprising:
shaping the semiconductor structure into a mesa after the implanting of the ions, wherein the light outcoupling surface corresponds to a base of the mesa.
4. The method of claim 1 , wherein the active light emitting layer includes quantum wells, and wherein intermixing of the ions as a result of the implanting and the annealing increases a bandgap at edges of the quantum wells.
5. The method of claim 1 , wherein the electron diffusion length is an electron diffusion length of:
a material of the p-side semiconductor layer,
a material of the n-side semiconductor layer, or
a material of the active light emitting layer.
6. The method of claim 2 , further comprising:
forming a mask over the p contact, wherein the mask shades the central region during the implanting of the ions.
7. The method of claim 2 , wherein the outer region has an annular cross section.
8. The method of claim 1 , wherein the light outcoupling surface is a bottom surface of the n-side semiconductor layer, and wherein the ions are implanted through a top surface of the p-side semiconductor layer.
9. The method of claim 8 , wherein the ions are implanted to a depth within the active light emitting layer.
10. The method of claim 8 , wherein the ions are implanted to a depth within the n-side semiconductor layer.
11. A light-emitting diode, comprising:
a substrate; and
a semiconductor structure formed on the substrate, the semiconductor structure comprising a p-side semiconductor layer, an n-side semiconductor layer, an active light emitting layer between the p-side semiconductor layer and the n-side semiconductor layer, and a light outcoupling surface facing the substrate, wherein:
an outer region of the semiconductor structure contains ions that have been implanted and intermixed with atoms within the outer region such that a bandgap of the outer region is increased relative to the outer region without the intermixed ions, and
the light outcoupling surface has a diameter less than twice an electron diffusion length of a material of the semiconductor structure.
12. The light-emitting diode of claim 11 , wherein the active light emitting layer includes quantum wells, and wherein the intermixed ions increase a bandgap at edges of the quantum wells.
13. The light-emitting diode of claim 11 , wherein the electron diffusion length is an electron diffusion length of:
a material of the p-side semiconductor layer,
a material of the n-side semiconductor layer, or
a material of the active light emitting layer.
14. The light-emitting diode of claim 11 , wherein the semiconductor structure has a mesa shape, and wherein the light outcoupling surface corresponds to a base of the mesa.
15. The light-emitting diode of claim 11 , further comprising:
a p contact formed over the p-side semiconductor layer, wherein the p contact defines an approximate boundary between the outer region and a central region of the semiconductor structure.
16. The light-emitting diode of claim 15 , wherein the outer region has an annular cross section.
17. The light-emitting diode of claim 11 , wherein the light outcoupling surface is a bottom surface of the n-side semiconductor layer, and wherein the ions were implanted through a top surface of the p-side semiconductor layer.
18. The light-emitting diode of claim 17 , wherein the ions were implanted to a depth within the active light emitting layer.
19. The light-emitting diode of claim 17 , wherein the ions were implanted to a depth within the n-side semiconductor layer.
20. The light-emitting diode of claim 17 , wherein the p-side semiconductor layer includes multiple semiconductor layers comprising different semiconductor materials, and wherein the ions were implanted to a depth within a bottommost layer of the multiple semiconductor layers.