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 method of manufacturing a light emitting device, the method comprising:
removing a substrate from a layer of n-type GaN of the light emitting device to expose a surface of the layer of n-type GaN;
placing a mask onto the layer of n-type GaN, the mask comprising one or more regions for blocking ions and one or more regions for passing ions; and
exposing the layer of n-type GaN through the mask to ion implantation to form a region of a varying refractive index in the layer of n-type GaN, the region of the varying refractive index comprising implanted ions and positioned to overlap an active region configured to emit light, wherein the refractive index of the region of the varying refractive index overlapping the active region is nonuniform in at least a direction perpendicular to a surface-normal direction of the exposed surface of the layer of n-type GaN.
2. The method of manufacturing the light emitting device of claim 1 , further comprising assembling the substrate back onto the layer of n-type GaN.
3. The method of manufacturing the light emitting device of claim 1 , wherein a region of the mask in the one or more regions for passing ions has a circular or rectangular shaped cross section.
4. The method of manufacturing the light emitting device of claim 3 , wherein a thickness of the region of the mask varies from a center of the region of the mask to a perimeter of the region of the mask.
5. The method of manufacturing the light emitting device of claim 4 , wherein a thickness of the region of the mask varies according to a parabolic curve radially from the center to the perimeter.
6. The method of manufacturing the light emitting device of claim 1 , wherein placing the mask onto the layer of n-type GaN comprises aligning a center of a region of the mask in the one or more regions for passing ions to a center of the active region of the layer of n-type GaN.
7. The method of manufacturing the light emitting device of claim 1 , wherein the region of the varying refractive index is column-shaped.
8. The method of manufacturing the light emitting device of claim 1 , wherein the region of the varying refractive index has a cross-section that is circular shaped.
9. The method of manufacturing the light emitting device of claim 1 , wherein the region of the varying refractive index has a cross-section that is rectangular shaped.
10. The method of manufacturing the light emitting device of claim 1 , wherein the region of the varying refractive index is configured to alter a light path of the light.
11. The method of manufacturing the light emitting device of claim 1 , wherein the region of the varying refractive index is configured to perform at least one of focusing the emitted light or increasing a light extraction efficiency of the light emitting device.
12. The method of manufacturing the light emitting device of claim 1 , wherein the layer of n-type GaN comprises a second region at least partially enclosing the region of the varying refractive index and including implanted ions.
13. The method of manufacturing the light emitting device of claim 12 , wherein a dose of implanted ions in the second region is at least the same as a dose of implanted ions in the region of the varying refractive index.
14. The method of manufacturing the light emitting device of claim 12 , wherein the region of the varying refractive index and the second region are contiguous.
15. The method of manufacturing the light emitting device of claim 1 , wherein the region of the varying refractive index has a refractive index in the range of 2.1 to 2.55.
16. The method of manufacturing the light emitting device of claim 1 , wherein the light emitting device is based on a multi-layer epitaxial thin film structure.