HYBRID VERTICAL CAVITY OF MULTIPLE WAVELENGTH LEDS

• US 20090001389A1
• Filed: 06/28/2007
• Published: 01/01/2009
• Est. Priority Date: 06/28/2007
• Status: Abandoned Application

• Current Assignee: Motorola Mobility, Inc. (Lenovo Group Ltd.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: WANG, DONGXUE, JOHNSON, KEVIN W.
• Application Number:
  US11/769,977
• Publication Number:
  US 20090001389A1
• Time in Patent Office: Days
• US Class Current: 257/89
• CPC Class Codes: H01L 27/15 including semiconductor components having potential barriers, specially adapted for light emission
• CPC Class Codes: H01L 33/105 with a resonant cavity structure
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector

Abstract

A solid state device (200) for a hybrid vertical cavity of multiple wavelength LEDs is provided. The solid state device can include a hybrid vertical cavity formed by a cascading of a first sub-cavity (210) and a second sub-cavity (220) to share a mirror (350) within the solid state device. The hybrid vertical cavity can collimate the first accumulated light (213) and the second accumulated light (223) to increase an efficiency of total emitted light. In one arrangement, the total emitted light can be directed to a phosphor to generate a white light.

Claims

1. A solid state device suitable for use with light emitting diodes or semiconductor laser diodes, comprising

a hybrid vertical micro-cavity formed by a cascading of two sub-cavities to share a mirror within the solid state device,

wherein the hybrid vertical cavity collimates the first accumulated light and the second accumulated light to increase an efficiency of total emitted light.

2. The solid state device of claim 1, wherein the two sub-cavities comprise

a first vertical cavity formed between a first filter and the mirror with a first LED between the first filter and the mirror, and the first LED emits a first light with a peak wavelength λ

₁ that is reflected by the first filter back within the first cavity, wherein the first filter collimates the first light to produce a first accumulated light, and

a second vertical cavity formed between a second filter and the mirror with a second LED between the second filter and the mirror, and the second LED emits a second light with a peak wavelength λ

₂ that is reflected by the second filter back within the second cavity, wherein the second filter collimates the second light to produce a second accumulated light.

3. The solid state device of claim 2, wherein

the first filter is a first Distributed Bragg Grating (DBG) reflector that reflects an optical spectrum with a peak wavelength λ

₁ of the first light back within the first cavity; and

the second filter is a second Distributed Bragg Grating (DBG) reflector that reflects an optical spectrum with a peak wavelength λ

₂ of the second light back within the second cavity,

wherein the DBR is fabricated using AlGaN/GaN layers, and these layers are p-doped to improve conductivity.

4. The solid state device of claim 2, wherein the first LED emits a green light or blue light, and the second LED emits a blue light or ultraviolet light, respectively, wherein a length of the first cavity is longer than a length of the second cavity to accommodate a longer wavelength of the green or blue light.

5. The solid state device of claim 2, wherein the size, dimension, and position of a LED varies in accordance with a wavelength of light emitted by the LED and optical power of the LED.

6. The solid state device of claim 2, wherein hybrid vertical cavity is used to mix green and blue, or blue and UV, respectively, to produce mixed light, and the mixed light pumps special designed phosphors to collectively produce a white light;

and the cavity is also used to mix RGB monochromatic light.

7. The solid state device of claim 6, wherein the white light is used for at least one among display backlighting, keyboard lighting, camera flash. projector lighting, and mixed Green and Blue or Blue and UV can be used in areas of projection, camera flash, bio-application, DNA or molecule identification, and optical data storage on a CD or DVD.

8. The solid state device of claim 6, wherein the first LED emits a green/blue light in the first vertical cavity, and the second LED emits a blue/UV light in the second vertical cavity, the vertical hybrid cavity collimates the blue/UV light and the green/Blue light to produce a mixed light that is directed to a pump phosphor that emits corresponding light responsive to receiving the mixed light. The pumping light from LEDs and light emitted from phosphors collectively form white light. The amount of monochromatic light from each of the dual-wavelength LED can be used to control the color temperature of the white light.

9. A solid state device to form a hybrid vertical cavity of multiple wavelength LEDS, the solid state device comprising:

a substrate that is transparent to light;

a first filter for the first LED to reflect a first light within a first vertical cavity, accumulate the first light within the first cavity, and emit the first light through the substrate;

a first LED coupled to the substrate to emit the first light;

a second filter for the second LED to reflect a second light within a second vertical cavity, accumulate the second light within the second cavity, and emit the second light outside of the second vertical cavity through the first LED, the first filter, and the substrate;

a second LED layered on the second filter to emit the second light; and

a mirror layered on the second LED to reflect the first light within the first cavity and to reflect the second light within the second cavity.

10. The solid state device of claim 9, wherein the first LED or the second LED comprise a n-GaN layer, an active region consisting of InGaN/GaN multiple quantum well (MQW) layered on the n-GaN layer, and a p-GaN layered on the first active region. The amount of Indium in InGaN of MQW determines the peak wavelength of emissions

11. The solid state device of claim 9, further comprising at least one more LED and at least one more filter to create at least one more vertical cavity within the solid state device.

12. The solid state device of claim 9, wherein the hybrid vertical cavity serves as a light collimator to increase a light pumping efficiency of a phosphor coated on the solid state device.

13. The solid state device of claim 9, wherein the first filter or the second filter is Distributed Bragg Grating (DBG) reflectors having layer thicknesses for AlGaN/GaN reflectivity index corresponding to a peak wavelength of the corresponding first LED or second LED, respectively.

14. The solid state device of claim 9, wherein the hybrid vertical cavity is formed by cascading the first vertical cavity with the second vertical cavity to share the mirror.

15. The solid state device of claim 9, wherein the first filter is switched with the mirror to create a top emitting LED device instead of a bottom emitting LED device.

16. The solid state device of claim 9, wherein a major amount of light is emitted through the substrate by flip-chip packaging to provide a substrate emitting device.

17. A solid state device to emit dual wavelength light within a hybrid vertical cavity, comprising

a first LED that emits a first light within a first vertical cavity which is reflected within the first vertical cavity and accumulated by a first filter that produces a first accumulated light, wherein the first vertical cavity is formed between a first filter and a mirror, and the first light passes through a second filter and a second LED inside the first vertical cavity;

and

a second LED that emits a second light within a second vertical cavity which is reflected within the second vertical cavity and accumulated by a second filter that produces a second accumulated light, wherein the second vertical cavity is formed between the second filter and the mirror, and the second accumulated light passes through the first LED and the first filter outside of the second vertical cavity.

18. The solid state device of claim 17, wherein first filter and the second filter are composed of aluminium gallium nitride (AlGaN) and GaN and are monolithically integrated with the first LED and the second LED to share the mirror.

19. The solid state device of claim 17, wherein the first filter reflects green (blue) light, and the second filter reflects blue (ultraviolet) light and transmits green (blue) light,

wherein the vertical hybrid cavity collimates the green light (blue) and the blue (UV) light to produce a mixed light, and directs the mixed light to a phosphor that emits white light responsive to receiving the mixed light. The pumping light from LEDs and light emitted from phosphors collectively form white light. The amount of monochromatic light from each of the dual-wavelength LED can be used to control the color temperature of the white light.

20. The solid state device of claim 17, wherein the first LED includes a MQW active region to emit a green (or blue) light in the first vertical cavity, and the second LED includes a second MQW active region to emit a blue (or UV) light in the second vertical cavity, respectively,

wherein the first vertical cavity is longer than the second vertical cavity to accommodate a longer wavelength of the green light.

21. The solid state device of claim 17, wherein the mirror is a metal material or a dielectric material, such that the light can be transmitted through the dielectric material by multiple reflections and transmissions.

22. The solid state device of claim 21, further comprising a phosphor layered on the solid state device to emit corresponding light responsive to receiving the dual wavelength light to mixed light from LEDs to form white light, wherein light emitted by the first LED and the second LED is collected from both a substrate of the solid state device and the mirror and directed to the phosphor.