GRIN lens structure in micro-LED devices
A GaN layer of micro-LEDs is exposed to ion implantation to amorphize one or more regions of the GaN layer. As a result, the GaN layer through which light rays propagate have non-uniform refractive indexes that modify propagation paths of some light rays. Ions are implanted in a region overlapping an active region that emits light to function as a converging GRIN (gradient-index) lens. The ion implanted regions collimate light rays that propagate along predetermined directions. As such, the light extraction from and the focus of the micro-LEDs is increased.
1. A light emitting diode, comprising:
a first layer of semiconductor material;
an active region on the first layer of semiconductor material; and
a second layer of semiconductor material on the active region, the active region configured to emit light through the second layer of semiconductor material in response to a potential difference applied between the first layer and the second layer of semiconductor material;
wherein the second layer of semiconductor material comprises a first region positioned to overlap the active region, wherein the first region has a refractive index profile that changes gradually in a radial direction from a center of the first region.
2. The light emitting diode of claim 1 , wherein doses of implanted ions in the first region of the second layer of semiconductor material vary radially from a center of the first region to a perimeter of the first region.
3. The light emitting diode of claim 1 , wherein doses of implanted ions in the first region of the second layer of semiconductor material increase from a center of the first region to a perimeter of the first region.
4. The light emitting diode of claim 3 , wherein a profile of the doses is represented as a parabolic curve that decreases from the center of the second layer of semiconductor material towards a perimeter of the second layer of semiconductor material.
5. The light emitting diode of claim 1 , wherein doses of implanted ions in the first region of the second layer of semiconductor material are selected such that the first region collimates at least part of the light passing through the first region.
6. The light emitting diode of claim 1 , wherein the first region is column-shaped.
7. The light emitting diode of claim 1 , wherein the first region has a cross-section that is circular shaped.
8. The light emitting diode of claim 1 , wherein the first region has a cross-section that is rectangular shaped.
9. The light emitting diode of claim 1 , wherein the first region is configured to alter a light path of the light.
10. The light emitting diode of claim 1 , wherein the first region is configured to perform at least one of focusing the light and increasing a light extraction efficiency of the light emitting diode.
11. The light emitting diode of claim 1 , wherein the second layer of semiconductor material comprises a second region partially enclosing the first region and including implanted ions.
12. The light emitting diode of claim 11 , wherein a dose of implanted ions in the second region is at least the same as a dose of implanted ions in the first region.
13. The light emitting diode of claim 11 , wherein the first region and the second region are contiguous.
14. The light emitting diode of claim 1 , wherein the first region has a refractive index in the range of 2.1 to 2.55.
15. The light emitting diode of claim 1 , wherein the light emitting diode is based on a multi-layer epitaxial thin film structure.