Wavelength converted semiconductor light emitting device
View Patent ↗A device includes a semiconductor structure comprising a light emitting layer disposed between an n-type region and a p-type region. A luminescent material is positioned in a path of light emitted by the light emitting layer. A thermal coupling material is disposed in a transparent material. The thermal coupling material has a thermal conductivity greater than a thermal conductivity of the transparent material. The thermal coupling material is positioned to dissipate heat from the luminescent material.
1. A device comprising:
a semiconductor structure comprising a light emitting layer;
a luminescent material positioned in a path of light emitted by the light emitting layer; and
a thermal coupling material disposed in a transparent material; wherein:
the thermal coupling material is non-wavelength converting of light emitted by the light emitting layer;
the thermal coupling material has a thermal conductivity greater than a thermal conductivity of the transparent material;
the thermal coupling material is positioned to dissipate heat from the luminescent material;
the thermal coupling material comprises particles having a median particle size greater than 10 μm; and
an index of refraction of the thermal coupling material differs from an index of refraction of the transparent material by less than 10%.
2. The device of claim 1 wherein the luminescent material is a powder phosphor disposed in the transparent material.
3. The device of claim 1 wherein:
the luminescent material is a first luminescent material configured to emit light at a first peak wavelength;
the device further comprises a second luminescent material configured to emit light at a second peak wavelength; and
the first and second luminescent materials are mixed and disposed in the transparent material.
4. The device of claim 1 wherein:
the luminescent material is a first luminescent material configured to emit light at a first peak wavelength;
the device further comprises a second luminescent material configured to emit light at a second peak wavelength; and
the first and second luminescent materials are disposed in transparent material and positioned over the semiconductor structure in discrete layers.
5. The device of claim 1 wherein the luminescent material is a ceramic phosphor.
6. The device of claim 1 further comprising a powder phosphor disposed in the transparent material.
7. The device of claim 1 wherein the transparent material is formed into a lens and the transparent material is disposed between the semiconductor structure and the luminescent material.
8. The device of claim 1 wherein the light emitting layer is a III-nitride material.
9. The device of claim 1 wherein the thermal coupling material has a thermal conductivity of at least 5 W/m-° C.
10. The device of claim 1 wherein the thermal coupling material comprises a powder with a median particle size of between 10 μm and 50 μm.
11. The device of claim 1 wherein the thermal coupling material comprises a powder, wherein at least a portion of the thermal coupling material particles are in direct contact with nearest neighbor particles and form a thermally conductive path to the semiconductor structure.
12. The device of claim 1 , wherein a density of the thermal coupling material is sufficient to assure that a substantial majority of the thermal material particles are in contact with each other.
13. The device of claim 1 , wherein a ratio of the thermal coupling material compared to the transparent material by weight is at least 1.5:1.
14. The device of claim 1 , wherein a ratio of the thermal coupling material compared to the luminescent material by weight is at least 4:1.
15. A method comprising:
providing a semiconductor structure comprising a light emitting layer;
positioning a luminescent material in a path of light emitted by the light emitting layer; and
positioning a thermal coupling material disposed in a transparent material to dissipate heat from the luminescent material;
wherein:
the thermal coupling material is non-wavelength converting of light emitted by the light emitting layer;
the thermal coupling material has a thermal conductivity greater than a thermal conductivity of the transparent material;
the thermal coupling material comprises particles having a median particle size greater than 10 μm; and
an index of refraction of the thermal coupling material differs from an index of refraction of the transparent material by less than 10%.
16. The method of claim 15 wherein the luminescent material is a ceramic phosphor.
17. The method of claim 15 , wherein a density of the thermal coupling material is sufficient to assure that a substantial majority of the thermal material particles are in contact with each other.
18. The method of claim 15 , wherein a ratio of the thermal coupling material compared to the transparent material by weight is at least 1.5:1.
19. The method of claim 15 , wherein a ratio of the thermal coupling material compared to the luminescent material by weight is at least 4:1.