Light Emitting Device Including a Photonic Crystal and a Luminescent Ceramic
A semiconductor structure including a light emitting layer disposed between an n-type region and a p-type region and a photonic crystal formed within or on a surface of the semiconductor structure is combined with a ceramic layer which is disposed in a path of light emitted by the light emitting layer. The ceramic layer is composed of or includes a wavelength converting material such as a phosphor.
1 . A device comprising:
a semiconductor structure comprising:
a light emitting layer disposed between an n-type region and a p-type region; and
a variation in refractive index formed within or on a surface of the semiconductor structure; and
a ceramic layer disposed in a path of light emitted by the light emitting layer, the ceramic layer comprising a wavelength converting material.
2 . The device of claim 1 wherein the ceramic layer comprises a rigid agglomerate of phosphor particles.
3 . The device of claim 1 wherein the variation in refractive index comprises a random arrangement of features, wherein a lateral extent of each feature is less than twice a peak emission wavelength of the light emitting layer.
4 . The device of claim 1 wherein the variation in refractive index comprises a random arrangement of features, wherein a lateral extent of each feature is more than twice a peak emission wavelength of the light emitting layer.
5 . The device of claim 1 wherein the variation in refractive index comprises a periodic arrangement of features, wherein the arrangement of features has a period more than twice a peak emission wavelength of the light emitting layer.
6 . The device of claim 1 wherein the variation in refractive index is periodic.
7 . The device of claim 1 wherein the variation in refractive index is a photonic crystal.
8 . The device of claim 7 wherein the photonic crystal comprises a periodic variation in a thickness of the n-type region.
9 . The device of claim 7 wherein the photonic crystal comprises a planar lattice of holes.
10 . The device of claim 7 wherein a distance between a center of the light emitting layer and the photonic crystal is less than about 4λ, where λ is a wavelength in the semiconductor structure of light emitted by the light emitting layer.
11 . The device of claim 1 wherein a total thickness of semiconductor layers in the device is less than about 1 μm.
12 . The device of claim 1 wherein a total thickness of semiconductor layers in the device is less than about 0.5 μm.
13 . The device of claim 1 wherein a surface of the ceramic layer comprises a lens.
14 . The device of claim 1 wherein a surface of the ceramic layer is textured.
15 . The device of claim 1 further comprising a host substrate, wherein the semiconductor structure is attached to the host substrate and the ceramic layer is disposed proximate a surface of the semiconductor structure opposite the host substrate.
16 . The device of claim 1 wherein the wavelength converting material comprises one of (Lu 1-x-y-a-b Y x Gd y ) 3 (Al 1-z Ga z ) 5 O 12 :Ce a Pr b wherein 0<x<1, 0<y<1, 0<z≦0.1, 0<a≦0.2 and 0<b≦0.1; Lu 3 Al 5 O 12 :Ce 3+ ; and Y 3 Al 5 O 12 :Ce 3+ .
17 . The device of claim 1 further comprising a light valve disposed between the semiconductor structure and the ceramic layer.
18 . The device of claim 17 wherein the light valve comprises one of a dielectric stack, a distributed Bragg reflector, a dichroic filter, a two-dimensional photonic crystal, and a three-dimensional photonic crystal.
19 . The device of claim 17 wherein the variation in refractive index is configured to emit light in a predetermined angular emission profile and wherein the light valve is configured to transmit a majority of light emitted in the predetermined emission profile and incident on the light valve.
20 . The device of claim 19 wherein more than 60% of light escaping the semiconductor structure is emitted into a cone 45° from a normal to a major surface of the semiconductor structure and more than 90% of the light emitted into the 45° cone is transmitted by the light valve.
21 . The device of claim 20 wherein less than 10% of the light emitted by the ceramic is transmitted by the light valve.
22 . The device of claim 17 wherein the light valve is spaced apart from the semiconductor structure.
23 . The device of claim 17 further comprising a transparent material disposed between the light valve and the semiconductor structure, wherein the transparent material has an index of refraction greater than 1.4.
24 . The device of claim 17 further comprising a dielectric concentrator disposed in a path of light emitted by the light emitting layer.
25 . The device of claim 24 wherein the ceramic layer is disposed between the dielectric concentrator and the semiconductor structure.
26 . The device of claim 24 wherein the dielectric concentrator is disposed between the semiconductor structure and the ceramic layer.
27 . The device of claim 24 wherein the dielectric concentrator is disposed between the light valve and the ceramic layer.
28 . The device of claim 24 wherein the dielectric concentrator is a glass lens.
29 . The device of claim 24 wherein the variation in refractive index is configured to emit light in a predetermined angular emission profile and wherein the dielectric concentrator is configured such that a majority of light emitted in the predetermined emission profile is emitted into the dielectric concentrator.
30 . The device of claim 1 further comprising a reflective layer, wherein the ceramic layer is disposed between the reflective layer and the semiconductor structure.
31 . The device of claim 30 wherein the reflective layer is disposed on a surface of the ceramic layer such that a majority of light escaping the device is emitted light from sides of the ceramic which are substantially perpendicular to a major surface of the light emitting layer.
32 . The device of claim 30 wherein the reflective layer comprises one of a specular and a diffusing reflector.
33 . The device of claim 30 wherein the reflective layer comprises one of aluminum, silver, titanium oxide, a distributed Bragg reflector, a dichroic, and a photonic crystal.