Efficient phosphor-conversion led structure

• US 6,155,699 A
• Filed: 03/15/1999
• Issued: 12/05/2000
• Est. Priority Date: 03/15/1999
• Status: Expired due to Term

• Current Assignee: Document Security Systems, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Miller, Jeffrey N., Mars, Danny E.
• Primary Examiner(s): Sember, Thomas M.
• Application Number:
  US09/268,764
• Time in Patent Office: 631 Days
• Field of Search: 362/293, 362/800, 362/84, 313/506, 313/502, 313/512, 313/112, 313/113, 313/114, 257/81, 257/94, 257/97, 257/99, 257/680, 257/91, 257/113, 257/95
• US Class Current: 362/293
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/507 the elements being in intimate contact with parts other than the semiconductor body or integrated with parts other than the semiconductor body
• CPC Class Codes: H01L 33/52 Encapsulations
• CPC Class Codes: H04N 9/30 using solid-state colour display devices
• CPC Class Codes: Y10S 362/80 Light emitting diode

Abstract

A light emitting device and a method of fabricating the device include a wavelength selective reflector that is formed between a light source and a layer of phosphorescent material. The light emitting device is a phosphor-conversion light emitting diode (LED) that outputs secondary light that is converted from primary light emitted from the light source. In the preferred embodiment, the light source is a Gallium Nitride (GaN) die and the wavelength selective reflector is a distributed Bragg reflector (DBR) mirror. The DBR mirror is comprised of multiple alternating layers of high and low refractive index materials. The high refractive index material may be Titanium Dioxide (TiO₂) and the low refractive index material may be Silicon Dioxide (SiO₂). An encapsulating layer over the GaN die provides a distance between the GaN die and the DBR mirror. Preferably, the encapsulating layer is a dome-shaped structure and the DBR mirror forms a dome-shaped shell over the encapsulating layer. In the most preferred embodiment, the dome-shaped configuration of the encapsulating layer and the DBR mirror is generally hemispheric. The dome-shaped configuration of the DBR mirror reduces the cone-angle average of the primary light from the light source, thereby improving the transmittance characteristic of the DBR mirror with respect to the primary light. Consequently, the amount of output light generated by the LED is significantly improved.

Claims

1. A light emitting device comprising:

a light generator responsive to an excitation signal for emitting first light in a wavelength range having a first peak wavelength;

a curved wavelength selective reflector that is spaced apart from the light generator by a predetermined distance, said wavelength selective reflector being substantially transmissive with respect to said first light that is propagating in a first direction away from said light generator, said wavelength selective reflector having a curved shape and being positioned to at least partially surround said light generator, said wavelength selective reflector being substantially reflective with respect to second light in a wavelength range having a second peak wavelength that is propagating in a second direction toward said light generator; and

a wavelength converter fixed at a side of said wavelength selective reflector opposite to said light generator to receive said first light propagating from said wavelength selective reflector in said first direction, said wavelength converter being responsive to said first light to generate said second light having said second peak wavelength.

2. The device of claim 1 wherein said wavelength selective reflector includes a first layer of a first refractive index material and a second layer of a second refractive index material, said first layer and said second layer having a dome shape extending at least partially about said light generator.

3. The device of claim 2 further comprising a dome-shaped structure of a transparent material positioned between said light generator and said wavelength selective reflector to separate said wavelength selective reflector from said light generator by said determined distance, said dome-shaped structure being positioned to at least partially surround said light generator.

4. The device of claim 2 wherein said first refractive index material has a higher refractive index than the refractive index of said second refractive index material, said wavelength selective reflector being hemispheric and having a radius that is at least 1.5 times a lateral dimension of said light generator, said light generator being light-emitting layers on a die.

5. The device of claim 4 wherein said high refractive index material includes Titanium Dioxide (TiO₂) and said low refractive index material includes Silicon Dioxide (SiO₂).

6. The device of claim 2 wherein said first layer and said second layer at least partially define a distributed Bragg reflector, said distributed Bragg reflector being configured to transmit said first light having said first peak wavelength and to reflect said second light having said second peak wavelength.

7. The device of claim 1 wherein said light generator includes a semiconductor chip that emits said first light in response to said excitation signal, said semiconductor chip having a generally planar light-emitting surface that is spaced apart from said wavelength selective reflector by said predetermined distance.

8. The device of claim 7 wherein said semiconductor chip is a Gallium Nitride (GaN) based chip that emits said first light having said first peak wavelength, said first peak wavelength being in a blue region of a light spectrum.

9. The device of claim 1 wherein said wavelength converter is a layer of a phosphorescent material having a property to convert light energy having said first peak wavelength into light energy having said second peak wavelength.

10. A method of fabricating a light emitting device comprising steps of:

providing a light source that emits first light having a first peak wavelength;

depositing a transparent material over said light source such that said light source is at least partially encapsulated by said transparent material and such that said transparent material has a curved outer surface that is spaced apart from said light source, said transparent material providing a propagation medium for said first light having said first peak wavelength;

forming a wavelength selective reflector over said curved outer surface of said transparent material such that said wavelength selective reflector has a curved inner surface, said wavelength selective reflector configured to transmit said first light having said first peak wavelength and to reflect second light having a second peak wavelength; and

depositing a layer of a phosphorescent material over said wavelength selective reflector, said phosphorescent material having a property of converting light energy having said first peak wavelength into light energy having said second peak wavelength.

11. The method of claim 10 wherein said step of depositing said transparent material includes a step of shaping said transparent material into a dome-shaped structure such that said light source is contained within said dome-shaped structure.

12. The method of claim 11 wherein said step of forming said wavelength selective reflector includes sequentially depositing a first refractive index material and a second refractive index material over said dome-shaped structure to form a first refractive index layer and an adjacent second refractive index layer that generally conform to an upper surface of said dome-shaped structure.

13. The method of claim 12 wherein said step of sequentially depositing said first refractive index material and said second refractive index material is a step of sequentially depositing Titanium Dioxide (TiO₂) and Silicon Dioxide (SiO₂).

14. The method of claim 10 wherein said step of providing said light source is a step of providing a Gallium Nitride (GaN) based chip that emits said first light having said first peak wavelength, said first peak wavelength being in a blue region of a light spectrum.

15. A light emitting device comprising:

a light source responsive to an applied signal to emit first light having a first peak wavelength, said light source including a semiconductor chip and a plurality of layers, said light source having a generally planar outer surface;

a transparent structure positioned over said light source such that said light source is at least partially encapsulated by said transparent structure, said transparent structure having a curved outer surface that is spaced apart from said generally planar outer surface of said light source;

a wavelength selective reflector having a curved inner surface coupled to said curved outer surface of said transparent structure such that said transparent structure is located between said light source and said wavelength selective reflector, said wavelength selective reflector configured to transmit said first light having said first peak wavelength propagating in a first direction away from said light source and to reflect second light having a second peak wavelength propagating in a second direction toward said light source; and

a layer of a phosphorescent material positioned over said wavelength selective reflector, said phosphorescent material having a property to absorb said first light having said first peak wavelength and generate said second light having said second peak wavelength.

16. The device of claim 15 wherein said transparent structure is a hemisphere-shaped structure and wherein said wavelength selective reflector is attached to an upper surface of said hemisphere-shaped structure such that said wavelength selective reflector forms a shell over said hemisphere-shaped structure.

17. The device of claim 16 wherein said wavelength selective reflector includes a first layer of a first refractive index material and a second layer of a second refractive index material, each of said first layer and said second layer being a hemisphere-shaped shell.

18. The device of claim 17 wherein said first refractive index material has a higher refractive index than a refractive index of said second refractive index material.

19. The device of claim 17 wherein said wavelength selective reflector includes a distributed Bragg reflector that is at least partially defined by said first layer and said second layer.

20. The device of claim 15 wherein said light source is a Gallium Nitride (GaN) based chip that emits said first light having said first peak wavelength, said first peak wavelength being in a blue region of a light spectrum.