Light emitting devices with optical elements and bonding layers
Light emitting devices with improved light extraction efficiency are provided. The light emitting devices have a stack of layers including semiconductor layers comprising an active region. The stack is bonded to a transparent optical element.
1. A device comprising:
a light emitting diode (LED) die comprising semiconductor layers including an active region, the LED die having a first coefficient of thermal expansion; and
a discrete and premade transparent optical element comprising a substantially flat bottom surface directly bonded to a top surface of the LED die, the transparent optical element having a second coefficient of thermal expansion approximately equal to the first coefficient of thermal expansion.
2. The device of claim 1 wherein the transparent optical element is selected from the group consisting of ZnS and ZnSe and the semiconductor layers comprise GaN.
3. The device of claim 1 wherein the transparent optical element is selected from the group consisting of Weierstrass sphere, hemisphere, portion of a sphere less than a hemisphere, ellipsoid, portion of an ellipsoid, and Fresnel.
4. The device of claim 1 wherein an index of refraction of the transparent optical element is graded.
5. A device comprising:
a light emitting diode (LED) die comprising a top surface and semiconductor layers including an active region, the LED die having a first coefficient of thermal expansion; and
a discrete and premade transparent optical element comprising a substantially flat bottom surface, the transparent optical element having a second coefficient of thermal expansion approximately equal to the first coefficient of thermal expansion; and
a bonding layer disposed between the top surface of the LED die and the bottom surface of the transparent optical element.
6. The device of claim 5 wherein:
the LED die comprises a metal contact;
an electrically conductive layer is disposed on a surface of the transparent optical element facing the LED die; and
the bonding layer is patterned to permit the metal contact to make electrical contact to the electrically conductive layer.
7. The device of claim 6 wherein the electrically conductive layer is indium tin oxide.
8. The device of claim 5 wherein the bonding layer is selected from the group consisting of ZnS and ZnSe and the semiconductor layers comprise GaN.
9. The device of claim 5 wherein:
the transparent optical element has a refractive index n lens ;
the bonding layer has a refractive index n bond ;
a top layer of the LED die has a refractive index n LED ; and
n LED ≤n bond ≤n lens .
10. The device of claim 5 wherein:
the transparent optical element has a refractive index n lens ;
the bonding layer has a refractive index n bond ;
a top layer of the LED die has a refractive index n LED ; and
n LED ≤n lens ≤n bond .
11. The device of claim 5 wherein:
the transparent optical element has a refractive index n lens ;
the bonding layer has a refractive index n bond ;
a top layer of the LED die has a refractive index n LED ; and
n bond ≤n LED ≤n lens .
12. The device of claim 5 wherein:
the transparent optical element has a refractive index n lens ;
the bonding layer has a refractive index n bond ;
a top layer of the LED die has a refractive index n LED ; and
n bond ≤n lens ≤n LED .
13. The device of claim 5 wherein:
the transparent optical element has a refractive index n lens ;
the bonding layer has a refractive index n bond ;
a top layer of the LED die has a refractive index n LED ; and
n lens ≤n bond ≤n LED .
14. The device of claim 5 wherein:
the transparent optical element has a refractive index n lens ;
the bonding layer has a refractive index n bond ;
a top layer of the LED die has a refractive index n LED ; and
n lens ≤n LED ≤n bond .
15. The device of claim 5 wherein:
the transparent optical element has a refractive index n lens ;
the bonding layer has a refractive index n bond ;
a top layer of the LED die has a refractive index n LED ; and
n lens =n LED =n bond .
16. A device comprising:
a light emitting diode (LED) die comprising a top surface and semiconductor layers including an active region, the LED die having a top layer with a refractive index n LED ; and
a discrete and premade transparent optical element comprising a substantially flat bottom surface directly bonded to a top surface of the LED die, the transparent optical element having a refractive index n lens , where n LED ≤n lens .
17. The device of claim 16 wherein the transparent optical element is selected from the group consisting of Weierstrass sphere, hemisphere, portion of a sphere less than a hemisphere, ellipsoid, portion of an ellipsoid, and Fresnel.
18. The device of claim 16 wherein the transparent optical element is selected from the group consisting of ZnS and ZnSe and the semiconductor layers comprise GaN.
19. The device of claim 16 further comprising luminescent material included in or on the transparent optical element.
20. The device of claim 19 , wherein the luminescent material comprises one of phosphor particles and quantum dots.
21. A device comprising:
a light emitting diode (LED) die comprising a top surface and semiconductor layers including an active region, the LED die having a top layer with a refractive index n LED ; and
a discrete and premade transparent optical element comprising a substantially flat bottom surface bonded to a top surface of the LED die, the transparent optical element having a refractive index n lens , where n LED ≤ lens ; and
a bonding layer disposed between the top surface of the LED die and the bottom surface of the transparent optical element.
22. The device of claim 21 wherein:
the LED die comprises a metal contact;
an electrically conductive layer is disposed on a surface of the transparent optical element facing the LED die; and
the bonding layer is patterned to permit the metal contact to make electrical contact to the electrically conductive layer.
23. The device of claim 22 wherein the electrically conductive layer is indium tin oxide.
24. The device of claim 21 wherein the bonding layer is selected from the group consisting of ZnS and ZnSe and the semiconductor layers comprise GaN.
25. The device of claim 21 further comprising luminescent material included in the bonding layer.
26. The device of claim 25 , wherein the luminescent material comprises one of phosphor particles and quantum dots.