Micro light emitting diode with high light extraction efficiency
A micro light emitting diode (LED) having a high light extraction efficiency includes a bottom conductive layer, a light emitting layer on the bottom conductive layer, and a top conductive structure on the light emitting layer. The micro LED additionally includes a conductive side arm electrically connecting the sidewall of the light emitting layer with the bottom conductive layer, and a reflective bottom dielectric layer arranged under the light emitting layer and above the bottom conductive layer. In some embodiments, the micro LED further includes an ohmic contact between the top conductive structure and the light emitting layer that has a small area and is transparent, thereby increasing the light emergent area and improving the light extraction efficiency.
1. A micro light emitting diode having a high light extraction efficiency comprising:
a bottom conductive layer;
a light emitting layer on the bottom conductive layer;
a top conductive structure on the light emitting layer;
a bottom dielectric layer positioned between the bottom conductive layer and the light emitting layer; and
a conductive side arm connecting a sidewall of a bottom layer of the light emitting layer and the bottom conductive layer, wherein:
the light emitting layer further comprises a first type of semiconductor layer, an active layer, and a second type of semiconductor layer in turn from top down;
the second type of semiconductor layer has a protruded top extending outside of the active layer and the first type of semiconductor layer;
a first end of the conductive side arm covers and contacts the protruded top of the second type of semiconductor layer, and a second end of the conductive side arm contacts the bottom conductive layer;
a lateral width of the bottom conductive layer is larger than a lateral width of the second type of semiconductor layer; and
a sidewall of the conductive side arm is aligned with a sidewall of the bottom conductive layer.
2. The micro light emitting diode according to claim 1 , further comprising an ohmic contact layer positioned between the top conductive structure and the light emitting layer.
3. The micro light emitting diode according to claim 1 , wherein:
the lateral width of the bottom conductive layer is larger than a lateral width of the bottom dielectric layer, so that the bottom conductive layer has a protruded top extending outside of the second type of semiconductor layer and the bottom dielectric layer; and
at least part of the conductive side arm is supported on the protruded top of the bottom conductive layer.
4. The micro light emitting diode according to claim 3 , wherein the lateral width of the bottom conductive layer is less than 2 μm.
5. The micro light emitting diode according to claim 3 , wherein a width of the protruded top of the bottom conductive layer is less than or equal to a width of the protruded top of the second type of semiconductor layer.
6. The micro light emitting diode according to claim 1 , wherein a material of the second type of top semiconductor layer is different from a material of the second type of bottom semiconductor layer.
7. The micro light emitting diode according to claim 1 , wherein:
the second type of top semiconductor layer is AlGaInP;
the second type of bottom semiconductor layer is GaP; and
the first type of semiconductor layer is AlInP.
8. The micro light emitting diode according to claim 1 , wherein:
the first end of the conductive side arm is in electrical contact with the protruded top of the second type of bottom semiconductor layer;
the first end of the conductive side arm is not in electrical contact with the second type of top semiconductor layer; and
the first end of the conductive side arm is not in electrical contact with the light emitting layer and the first type of semiconductor layer.
9. The micro light emitting diode according to claim 1 , wherein a lateral width of the first type of semiconductor layer is equal to or larger than a lateral width of the active layer.
10. The micro light emitting diode according to claim 1 , wherein a lateral width of the first type of semiconductor layer is much narrower than a lateral width of the active layer.
11. The micro light emitting diode according to claim 1 , wherein the conductive side arm has an inverted L shape.
12. The micro light emitting diode according to claim 1 , wherein the conductive side arm is attached and connected to a sidewall of the bottom dielectric layer.
13. The micro light emitting diode according to claim 1 , wherein:
the lateral width of the bottom conductive layer is larger than a lateral width of the bottom dielectric layer; and
a sidewall of the bottom conductive layer protrudes outside and beyond a sidewall of the conductive side arm.
14. The micro light emitting diode according to claim 1 , further comprising a transparent isolation layer, wherein:
the transparent isolation layer covers the protruded top of the second type of semiconductor layer, a top and a side wall of the conductive side arm, a sidewall of the light emitting layer, and a sidewall of the first type of semiconductor layer; and
the top conductive structure is positioned on top of the transparent isolation layer.
15. The micro light emitting diode according to claim 1 , wherein the first type of semiconductor layer is an N type semiconductor layer and the second type of semiconductor layer is a P type semiconductor layer.
16. The micro light emitting diode according to claim 1 , wherein the first type of semiconductor layer is a P type semiconductor layer and the second type of semiconductor layer is an N type semiconductor layer.
17. The micro light emitting diode according to claim 1 , further comprising an electric circuit base at a bottom of the bottom conductive layer, wherein:
the bottom conductive layer is used as a bonding layer that is bonded with a surface of the electric circuit base; and
the electric circuit base comprises a driving circuit that controls emission of the light emitting layer.
18. The micro light emitting diode according to claim 1 , wherein the micro light emitting diode has a light extraction efficiency of at least 40%.
19. The micro light emitting diode according to claim 1 , wherein the micro light emitting diode has a light extraction efficiency of at least 60%.
20. The micro light emitting diode according to claim 1 , wherein:
the second type of semiconductive layer further comprises a second type of top semiconductor layer and a second type of bottom semiconductor layer; and
the second type of bottom semiconductor layer extends outside relative to the second type of top semiconductor layer, thereby forming the protruded top extending outside of the active layer and the first type of semiconductor layer.