Solid state lighting device with reduced form factor including led with directional emission and package with microoptics

• US 20030209714A1
• Filed: 03/31/2003
• Published: 11/13/2003
• Est. Priority Date: 10/12/2000
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Krishnamurthy, Vikram Bidare, Taskar, Nikhil Ramesh
• Granted Patent: US 6,998,281 B2
• Time in Patent Office: Days
• US Class Current: 257/79
• CPC Class Codes: H01L 2224/32225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48235 connecting the wire to a via metallisation of the item
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 25/0753 the devices being arranged next to each other
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/01012 Magnesium [Mg]
• CPC Class Codes: H01L 2924/01079 Gold [Au]
• CPC Class Codes: H01L 2924/12041 LED
• CPC Class Codes: H01L 2933/0091 Scattering means in or on the semiconductor body or semiconductor body package H01L33/22 takes precedence
• CPC Class Codes: H01L 33/105 with a resonant cavity structure
• CPC Class Codes: H01L 33/405 Reflective materials
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/54 having a particular shape

Abstract

A light emitting device containing an array of directional emission LEDs is provided. The directional emission LEDs of the array may be substrate emitting, lateral current injection, resonant cavity LEDs mounted in a flip-chip configuration. Each LED may emit a different color of light, such that the output of the array appears white to an observer. The LED array package may contain microoptical elements, such as a diffraction grating or microprisms, integrated into the light emitting surface of the package. The microoptical elements are used to mix the light beams emitted by individual LEDs in the array.

Claims

1. A lateral current injection, directional emission light emitting diode, comprising:

a first conductivity type semiconductor contact layer;

a semiconductor active layer over a first surface of the first conductivity type semiconductor contact layer;

a second conductivity type semiconductor contact layer having a first surface over the active layer;

a first electrode contacting the first surface of the first conductivity type semiconductor contact layer;

a second electrode contacting the second conductivity type semiconductor contact layer; and

wherein the light emitting diode emits radiation substantially in one direction.

2. The light emitting diode of claim 1, further comprising:

a transparent substrate below a second surface of the first conductivity type semiconductor contact layer;

a first Bragg reflector above the first conductivity type contact layer; and

a first conductivity type confinement layer between the first Bragg reflector and the active layer.

3. The light emitting diode of claim 2, wherein:

the light emitting diode comprises a resonant cavity light emitting diode containing a resonant cavity including the first conductivity type confinement layer, the second conductivity type contact layer and the active layer, and having a thickness of t=[λ

_o*(2*N*π

−

φ

_OUTPUT−

φ

_BACK)]/(4*π

*n) or a thickness of t=Nλ

₀/2n, where N is an integer, λ

₀ is the resonant cavity light emitting diode tuned peak radiation output wavelength in air, n is the effective refractive index of the cavity, and φ

_OUTPUT and φ

_BACK are phase changes during reflection at the first Bragg reflector and the second electrode;

the first Bragg reflector comprises a plurality of alternating first and second layers, each having a thickness of λ

₀/4n, such that the first Bragg reflector reflectivity is less than the reflectivity of the second electrode; and

the light emitting diode emits radiation substantially in one direction through the transparent substrate.

4. The light emitting diode of claim 3, wherein:

the first conductivity type semiconductor contact layer comprises an n-type III-V semiconductor contact layer containing Ga and N;

the active layer comprises at least one III-V semiconductor quantum well containing In, Ga and N which emits light having a peak emission wavelength which is equal to the tuned peak radiation, λ

₀.

the second conductivity type semiconductor contact layer comprises a p-type III-V semiconductor contact layer containing Ga and N;

the first conductivity type confinement layer comprises an n-type III-V semiconductor contact layer containing Ga and N;

the first electrode comprises a metal electrode;

the second electrode comprises a reflective metal containing electrode having a reflectivity of about 85 to 95%, contacting an entire second surface of the second conductivity type semiconductor contact layer; and

the first Bragg reflector comprises a plurality of pairs of first and second layers, the first layer containing Ga and N and the second layer containing Al, Ga and N, the reflector having a reflectivity of about 60 to 70%.

5. The light emitting diode of claim 4, wherein:

the transparent substrate comprises a sapphire substrate;

the n-type contact layer comprises an N⁺ GaN layer;

the n-type confinement layer comprises an N GaN layer;

the p-type contact layer comprises a P⁺ GaN layer or a combination of a P⁺ GaN contact sublayer and a P AlInGaN, AlGaN or GaN confinement sublayer;

the active layer comprises an InGaN quantum well between the p-type contact layer and the n-type confinement layer;

the first Bragg reflector comprises a plurality of first GaN layers and a plurality of second AlGaN layers;

the first electrode comprises an Al layer and a Ti layer; and

the second electrode comprises

a nickel oxide layer or a gold doped nickel oxide layer; and

an Al layer or a second Bragg reflector.

6. The light emitting diode of claim 3, wherein the active layer comprises at least one III-V semiconductor quantum well containing In, Ga and N which emits light having a peak emission wavelength, λ

₁, which is less than the tuned peak radiation, λ

₀, such that the angular distribution of the emitted radiation contains at least two intensity maxima.

7. The light emitting diode of claim 2, further comprising a second Bragg reflector located between the second electrode and the second conductivity type contact layer, the second Bragg reflector having a higher reflectivity than the first Bragg reflector.

8. The light emitting diode of claim 1, wherein the second electrode comprises a transparent conductive material and a Bragg reflector above the transparent conductive material.

9. The light emitting diode of claim 8, wherein:

the transparent conductive material comprises nickel oxide or gold doped nickel oxide; and

the Bragg reflector comprises a stack of alternating, electrically insulating layers.

10. The light emitting diode of claim 1, further comprising an insulating layer formed on at least a sidewall of the semiconductor active layer and a sidewall of the second conductivity type contact layer.

11. The light emitting diode of claim 1, further comprising:

a transparent substrate below a second surface of the first conductivity type semiconductor contact layer; and

a reflective layer substantially covering the at least one sidewall of the first conductivity contact layer.

12. The light emitting diode of claim 11, wherein the reflective layer comprises an electrode that covers at least one beveled sidewall of the first conductivity contact layer and at least one sidewall of the transparent substrate to reflect radiation emitted by the active layer substantially in one direction through the transparent substrate.

13. The light emitting diode of claim 1, further comprising:

a package containing a first lead, a second lead and a light emitting surface, wherein;

the first electrode electrically contacts the first lead;

the second electrode electrically contacts the second lead;

a transparent substrate positioned toward the light emitting surface in a flip chip configuration; and

a microoptical element positioned adjacent the light emitting surface.

14. The light emitting diode of claim 13, wherein the light emitting diode comprises a portion of an array of a plurality of light emitting diodes each emitting different color light.

15. The light emitting diode of claim 14, wherein the light emitting surface comprises an upper portion of an encapsulation material or a flexible sheet formed over the encapsulation material.

16. The light emitting diode of claim 15, wherein the microoptical element comprises a diffraction grating in the light emitting surface.

17. The light emitting diode of claim 15, wherein the microoptical element comprises a plurality of prisms in the light emitting surface.

18. An array of lateral current injection, resonant cavity light emitting diodes, comprising:

i) a plurality of lateral current injection, resonant cavity light emitting diodes, each emitting at a different peak emission wavelength, each light emitting diode comprising;

a) a transparent substrate;

b) a first conductivity type III-V semiconductor contact layer, having a first surface containing a contact region and a second surface over the transparent substrate;

c) a Bragg reflector over the first conductivity type contact layer;

d) a first conductivity type III-V semiconductor confinement layer over the Bragg reflector;

e) a III-V semiconductor quantum well active layer on the first conductivity type confinement layer and over the first surface of the first conductivity type contact layer;

f) a second conductivity type III-v semiconductor contact layer, having a first surface over the active layer;

g) a first metal electrode contacting the contact region of the first conductivity type contact layer; and

h) a second reflective electrode contacting the entire second surface of the second conductivity type contact layer;

ii) a package containing a plurality of first leads, a plurality of second leads and a light emitting surface, wherein;

a) the first electrodes electrically contact the first leads;

b) the second electrodes electrically-contact the second leads;

c) the transparent substrate of each light emitting diode is positioned toward the light emitting surface in a flip chip configuration; and

iii) a microoptical element integrated into the package adjacent the light emitting surface.

19. The array of claim 18, wherein:

the first conductivity type comprises n-type conductivity;

the second conductivity type comprises p-type conductivity;

the plurality of light emitting diodes each contain a resonant cavity comprising the p-type contact layer, the n-type confinement layer and the active layer, the cavity having a thickness of t=[λ

_o*(2*N*π

−

φ

_OUTPUT−

φ

_BACK)]/(4*π

*n) or a thickness of t=Nλ

₀/2n, where N is an integer, λ

₀ is the resonant cavity light emitting diode tuned peak radiation output wavelength in air, n is the effective refractive index of the cavity, and φ

_OUTPUT and φ

_BACK are phase changes during reflection at the Bragg reflector and second electrode;

the Bragg reflector comprises a plurality of alternating first and second layers, each having a thickness of λ

₀/4n, such that the Bragg reflector reflectivity is less than the reflectivity of the second electrode; and

the plurality of light emitting diodes emit radiation in one direction through the transparent substrate.

20. The array of claim 19, wherein:

the active layer comprises at least one GaInN quantum well, which emits radiation having a peak emission wavelength of about 365 to about 475 nm which is equal to the tuned peak radiation, λ

₀.

the second electrode comprises a reflective metal electrode having a reflectivity of about 85 to 95%;

the Bragg reflector comprises a plurality of pairs of first and second layers, the first layers comprising GaN and the second layer comprising AlGaN, the Bragg reflector having a reflectivity of about 60 to 70%;

the transparent substrate comprises a sapphire substrate;

the n-type contact layer comprises an N⁺ GaN layer;

the n-type confinement layer comprises an N GaN layer; and

the p-type contact layer comprises a P⁺ GaN layer.

21. The array of claim 19, wherein the active layer comprises at least one III-V semiconductor quantum well containing In, Ga and N which emits radiation having a peak emission wavelength, λ

₁, of about 365 to about 475 nm which is less than the tuned peak radiation, λ

₀, such that the emitted radiation contains at least two intensity maxima.

22. The array of claim 19, wherein:

the light emitting surface comprises an upper portion of an encapsulation material or of a flexible sheet formed over the encapsulation material; and

the microoptical element comprises a diffraction grating in the light emitting surface or a plurality of prisms in the light emitting surface.

23. A method of making a light emitting diode, comprising:

forming a first conductivity type semiconductor contact layer on a substrate;

forming a semiconductor active layer over a first surface of the first conductivity type semiconductor contact layer;

forming a second conductivity type semiconductor contact layer over the active layer;

patterning the first conductivity type semiconductor layer, the second conductivity type semiconductor contact layer and the active layer;

forming a first metal containing electrode contacting the first conductivity type semiconductor contact layer;

forming a second metal containing electrode contacting the second conductivity type semiconductor contact layer; and

forming a package containing at least one integrated microoptical element above the light emitting diode.

24. The method of claim 23, wherein:

the substrate comprises a material which is transparent to the radiation emitted by the active layer;

the first conductivity type semiconductor contact layer comprises an n-type III-V semiconductor contact layer containing Ga and N;

the active layer comprises at least one III-V semiconductor quantum well containing In, Ga and N;

the second conductivity type semiconductor contact layer comprises a p-type III-V semiconductor contact layer containing Ga and N;

the first electrode contacts the first surface of the n-type contact layer.

25. The method of claim 24, further comprising:

mounting the light emitting diode in the package in a flip chip configuration, wherein;

the first electrode electrically contacts a first lead;

the second electrode electrically contacts a second lead;

the transparent substrate is positioned toward a light emitting surface of the package;

forming an encapsulating material over the transparent substrate;

forming a flexible sheet over the encapsulating material; and

etching the at least one microoptical element in the insulating sheet.

26. The method of claim 25, wherein the microoptical element comprises a diffraction grating or a plurality of prisms.

27. The method of claim 24, further comprising:

mounting the light emitting diode in a package in a flip chip configuration, wherein;

the first electrode electrically contacts a first lead;

the second electrode electrically contacts a second lead;

the transparent substrate is positioned toward a light emitting surface of the package;

placing the package into a mold containing a pattern of the at least one microoptical element;

placing an encapsulating material into the mold; and

solidifying the encapsulating material to form the at least one microoptical element in the light emitting surface of the encapsulating material.

28. The method of claim 25, wherein the microoptical element comprises a diffraction grating or a plurality of prisms.

29. The method of claim 28, wherein the light emitting surface of the encapsulating material is substantially flat and does not contain a dome lens.

30. The method of claim 24, further comprising:

determining a desired tuned peak radiation output wavelength, λ

₀, of the light emitting diode;

selecting a band gap of the GaInN quantum well active layer such that the light emitting diode emits radiation substantially in one direction through the transparent substrate at a peak wavelength of λ

₀;

forming a Bragg reflector above the n-type contact layer, the Bragg reflector comprising a plurality of alternating first and second layers, each having a thickness of λ

₀/4n, where n is an integer, such that the Bragg reflector reflectivity is less than the reflectivity of the second electrode; and

forming a resonant cavity comprising the p-type contact layer, the active layer, and an n-type confinement layer, and having a thickness of t=[λ

_o*(2*N*π

−

φ

_OUTPUT−

φ

_BACK)](4*π

*n) or a thickness of t=Nλ

₀/2n, where N is an integer, λ

₀ is the resonant cavity light emitting diode tuned peak radiation output wavelength in air, n is the effective refractive index of the cavity, and φ

_OUTPUT and φ

_BACK are the phase changes during reflection at the first Bragg reflector and second electrode.

31. The method of claim 24, further comprising:

determining the desired tuned peak radiation output wavelength, λ

₀, of the light emitting diode;

selecting a band gap of the GaInN quantum well active layer such that the light emitting diode emits radiation substantially in one direction through the transparent substrate at a peak wavelength of λ

₁<

λ

₀;

forming a Bragg reflector above the n-type contact layer, the Bragg reflector comprising a plurality of alternating first and second layers, each having a thickness of λ

₀/4n, where n is an integer, such that the Bragg reflector reflectivity is less than the reflectivity of the second electrode; and

forming a resonant cavity comprising the p-type contact layer, the active layer and an n-type confinement layer, and having a thickness of t=[λ

_o*(2*N*π

−

φ

_OUTPUT−

φ

_BACK)]/(4*π

*n) or a thickness of t=Nλ

₀/2n, where N is an integer, λ

₀ is the resonant cavity light emitting diode tuned peak radiation output wavelength in air, n is the effective refractive index of the cavity, and φ

_OUTPUT and φ

_BACK are the phase changes during reflection at the first Bragg reflector and second electrode.

32. The method of claim 24, wherein:

the step of patterning comprises patterning the p-type contact layer, the active layer and a top portion of the n-type contact layer in the same patterning step to expose a contact portion of the first surface of the n-type contact layer; and

the step of forming the first electrode comprises forming at least one metal layer over the contact portion of the first surface of the n-type contact layer and over the p-type contact layer and patterning the at least one metal layer to form the first electrode on the contact portion.

33. The method of claim 32, further comprising forming a reflective layer over the at least one sidewall and the contact portion of the first surface of the n-type contact layer and over the p-type contact layer and patterning the reflective layer to form a reflective electrode on the at least one sidewall of the n-type contact layer.

34. The method of claim 33, wherein the step of forming the first electrode and the step of forming the second electrode comprises forming an aluminum layer over the first and the second conductivity type contact layers and patterning the aluminum layer to form the first and the second electrodes.

35. The method of claim 24, wherein:

the step of patterning occurs after the step of forming the second metal containing electrode; and

the step of patterning comprises;

forming a first mask over the p-type contact layer;

etching the p-type contact layer, the active layer and a top portion of the n-type contact layer to expose a contact portion of the first surface of the n-type contact layer;

forming a second mask over the patterned p-type contact layer and the active layer and over the contact portion of the first surface of the n-type contact layer; and

reactive ion etching the n-type contact layer to form the n-type contact layer with a circular or oval cross section containing one beveled sidewall, where a second surface of the n-type contact layer is wider than the first surface of the n-type contact layer.

36. The method of claim 24, wherein the step of patterning comprises:

forming a first mask over the p-type contact layer;

reactive ion etching the p-type contact layer, the active layer and the n-type contact layer to form a mesa with a circular or oval cross section containing one beveled sidewall, where a second surface of the n-type contact layer is wider than the first surface of the n-type contact layer;

forming a second mask over the patterned p-type contact layer; and

etching the p-type contact layer and the active layer to expose a contact portion of the first surface of the n-type contact layer.

37. The method of claim 24, further comprising:

forming a passivation layer;

sawing, scribe-breaking or laser cutting the transparent substrate to form a plurality of light emitting diode chips emitting different color of light; and

packaging the plurality of light emitting diode chips in an array.