Directional light extraction from micro-LED via localization of light emitting area using mesa sidewall epitaxy

1. A micro-light emitting diode (micro-LED) device comprising:

a semiconductor mesa structure including:

at least a portion of an n-type semiconductor layer;

an active region configured to emit visible light; and

a p-type semiconductor layer;

an insulator layer including:

an undoped semiconductor passivation layer grown on sidewalls of the semiconductor mesa structure; and

a dielectric passivation layer characterized by a refractive index lower than a refractive index of the undoped semiconductor passivation layer;

a reflective metal layer deposited on the dielectric passivation layer; and

a micro-lens configured to collimate the visible light emitted by the active region,

wherein a ratio between a width of the micro-lens and a width of the active region is greater than 1.5.

2. The micro-LED device of claim 1 , wherein:

the width of the micro-lens is less than 3 μm;

a thickness of the dielectric passivation layer is between 10 nm and 300 nm; and

a thickness of the undoped semiconductor passivation layer is between 1 nm and 300 nm.

3. The micro-LED device of claim 1 , wherein the micro-lens includes a dielectric micro-lens.

4. The micro-LED device of claim 1 , wherein the ratio between the width of the micro-lens and the width of the active region is greater than 2.0.

5. The micro-LED device of claim 1 , wherein the reflective metal layer includes Al, Au, Ag, Pt, Ti, Cu, or a combination thereof.

6. The micro-LED device of claim 1 , wherein each of the n-type semiconductor layer, the active region, the p-type semiconductor layer, and the undoped semiconductor passivation layer includes a III-P semiconductor material.

7. The micro-LED device of claim 1 , wherein the sidewalls of the semiconductor mesa structure are outwardly tilted from the p-type semiconductor layer to the n-type semiconductor layer.

8. The micro-LED device of claim 1 , wherein the insulator layer includes one or more layers between the undoped semiconductor passivation layer and the dielectric passivation layer, the one or more layers including a dielectric material, a doped semiconductor material, an undoped semiconductor material, or a combination thereof.

9. The micro-LED device of claim 1 , wherein the refractive index of the dielectric passivation layer is lower than 2.4.

10. The micro-LED device of claim 1 , further comprising a transparent conductive layer on the n-type semiconductor layer.

11. A micro-light emitting diode (micro-LED) device comprising:

a backplane wafer;

an array of micro-LEDs bonded to the backplane wafer, each micro-LED of the array of micro-LEDs including:

a semiconductor mesa structure including:

at least a portion of an n-type semiconductor layer;

an active region configured to emit visible light; and

a p-type semiconductor layer;

an insulator layer including:

a first passivation layer on sidewalls of the semiconductor mesa structure and characterized by a refractive index matching a refractive index of active region; and

a second passivation layer characterized by a refractive index lower than the refractive index of the first passivation layer; and

a reflective metal layer deposited on the second passivation layer; and

an array of micro-lenses on the array of micro-LEDs, wherein:

each micro-lens of the array of micro-lenses is configured to collimate the visible light emitted by the active region of a respective micro-LED of the array of micro-LEDs, and

a ratio between a width of the micro-lens and a width of the active region is greater than 1.5.

12. The micro-LED device of claim 11 , wherein:

the first passivation layer includes an undoped semiconductor material layer epitaxially grown on the sidewalls of the semiconductor mesa structure; and

the second passivation layer includes a dielectric material.

13. The micro-LED device of claim 11 , wherein:

a pitch of the array of micro-LEDs is less than 3 μm;

a thickness of the first passivation layer is between 1 nm and 300 nm; and

a thickness of the second passivation layer is between 10 nm and 300 nm.

14. The micro-LED device of claim 11 , wherein the ratio between the width of the micro-lens and the width of the active region is greater than 2.0.

15. The micro-LED device of claim 11 , wherein the reflective metal layer includes Al, Au, Ag, Pt, Ti, Cu, or a combination thereof.

16. The micro-LED device of claim 11 , wherein each of the n-type semiconductor layer, the active region, the p-type semiconductor layer, and the first passivation layer includes a III-P semiconductor material.

17. The micro-LED device of claim 11 , wherein the sidewalls of the semiconductor mesa structure are outwardly tilted from the p-type semiconductor layer to the n-type semiconductor layer.

18. The micro-LED device of claim 11 , wherein the refractive index of the second passivation layer is lower than 2.4.

19. The micro-LED device of claim 11 , wherein the insulator layer includes one or more layers between the first passivation layer and the second passivation layer, the one or more layers including a dielectric material, a doped semiconductor material, an undoped semiconductor material, or a combination thereof.

20. The micro-LED device of claim 11 , wherein each micro-LED of the array of micro-LEDs further comprises a back metal reflector coupled to the p-type semiconductor layer and electrically connected to a drive circuit of the backplane wafer.