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 includes increasing a bandgap in an outer region of a semiconductor layer by implanting ions in the outer region of the semiconductor layer and subsequently annealing the outer region of the semiconductor layer to intermix the ions with atoms within the outer region of the semiconductor layer. The semiconductor layer includes an active light emitting layer. A light outcoupling surface of the semiconductor layer has a diameter that is less than twice an electron diffusion length of the semiconductor layer. The outer region of the semiconductor layer extends from an outer surface of the semiconductor layer to a central region of the semiconductor layer that is shaded by a mask during the implanting of the ions.
1. A method comprising:
increasing a bandgap in an outer region of a semiconductor layer by implanting ions in the outer region of the semiconductor layer and subsequently annealing the outer region of the semiconductor layer to intermix the ions with atoms within the outer region of the semiconductor layer, wherein:
the semiconductor layer comprises an active light emitting layer,
a light outcoupling surface of the semiconductor layer has a diameter that is less than twice an electron diffusion length of the semiconductor layer,
the outer region of the semiconductor layer extends from an outer surface of the semiconductor layer to a central region of the semiconductor layer that is shaded by a mask during the implanting of the ions, and
the semiconductor layer further comprises an n-side semiconductor layer and a p-side semiconductor layer.
2. The method of claim 1 , wherein the ions are implanted at an angle with respect to an axis normal to a plane of the mask such that some of the ions become implanted beneath the mask.
3. The method of claim 1 , wherein the mask is formed over a metal contact.
4. The method of claim 1 , further comprising:
determining a thickness of the mask as a function of an implantation energy of the ions and to achieve a specific implantation depth.
5. The method of claim 1 , further comprising:
shaping the semiconductor layer into a mesa after the implanting of the ions.
6. The method of claim 1 , wherein the active light emitting layer is located between the n-side semiconductor layer and the p-side semiconductor layer, and wherein the ions are implanted to a depth within the active light emitting layer.
7. The method of claim 1 , wherein the active light emitting layer is located between the n-side semiconductor layer and the p-side semiconductor layer, and wherein the ions are implanted to a depth past the active light emitting layer.
8. 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 due to an increased concentration of ions at the edges of the quantum wells.
9. The method of claim 1 , wherein intermixing of the ions as a result of the implanting and the annealing defines an intermixing region that has a cross-sectional annular shape.
10. 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.
11. A light-emitting diode comprising:
a semiconductor layer comprising an active light emitting layer, an n-side semiconductor layer, and a p-side semiconductor layer, wherein:
a light outcoupling surface of the semiconductor layer has a diameter that is less than twice an electron diffusion length of the semiconductor layer,
an outer region of the semiconductor layer includes ions that were implanted and intermixed with atoms within the outer region of the semiconductor layer, and
a bandgap in the outer region of the semiconductor layer is greater than a bandgap in a central region of the semiconductor layer due to the ions being intermixed with the atoms within the outer region.
12. The light-emitting diode of claim 11 , further comprising:
a metal contact located on a top surface of the semiconductor layer and in the central region, wherein due to the ions being implanted at an angle with respect to an axis normal to a plane of the metal contact, some of the ions are implanted beneath the metal contact.
13. The light-emitting diode of claim 11 , wherein the active light emitting layer is located between the n-side semiconductor layer and the p-side semiconductor layer, and wherein the ions are implanted to a depth within the active light emitting layer.
14. The light-emitting diode of claim 11 , wherein the active light emitting layer is located between the n-side semiconductor layer and the p-side semiconductor layer, and wherein the ions are implanted to a depth past the active light emitting layer.
15. The light-emitting diode of claim 14 , further comprising:
a substrate in contact with the light outcoupling surface of the semiconductor layer, wherein the ions are implanted to a depth before the substrate.
16. The light-emitting diode of claim 11 , wherein the active light emitting layer includes quantum wells, and wherein due to an increased concentration of the ions at edges of the quantum wells, a bandgap at the edges of the quantum wells is greater than at a center of the quantum wells.
17. The light-emitting diode of claim 11 , wherein the outer region has a cross-sectional annular shape.
18. 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.
19. The light-emitting diode of claim 11 , wherein the electron diffusion length is an electron diffusion length of a material of the n-side semiconductor layer.
20. The light-emitting diode of claim 11 , wherein the electron diffusion length is an electron diffusion length of a material of the active light emitting layer.