DEEP ULTRAVIOLET LIGHT EMITTING DEVICES AND METHODS OF FABRICATING DEEP ULTRAVIOLET LIGHT EMITTING DEVICES

• US 20080142783A1
• Filed: 02/13/2008
• Published: 06/19/2008
• Est. Priority Date: 05/27/2005
• Status: Active Grant

• Current Assignee: CREE Led Incorporated (Smart Global Holdings Incorporated)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Bergmann, Michael John, Emerson, David Todd, Haberern, Kevin, Abare, Amber
• Granted Patent: US 8,772,757 B2
• Time in Patent Office: Days
• US Class Current: 257/13
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/12 with a stress relaxation structure, e.g. buffer layer
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

Light emitting devices and methods of fabricating light emitting devices that emit at wavelengths less than 360 nm with wall plug efficiencies of at least than 4% are provided. Wall plug efficiencies may be at least 5% or at least 6%. Light emitting devices and methods of fabricating light emitting devices that emit at wavelengths less than 345 nm with wall plug efficiencies of at least than 2% are also provided. Light emitting devices and methods of fabricating light emitting devices that emit at wavelengths less than 330 nm with wall plug efficiencies of at least than 0.4% are provided. Light emitting devices and methods of fabricating light emitting devices having a peak output wavelength of not greater than 360 nm and an output power of at least 5 mW, having a peak output wavelength of 345 nm or less and an output power of at least 3 mW and/or a peak output wavelength of 330 nm or less and an output power of at least 0.3 mW at a current density of less than about 0.35 μA/μm² are also provided. The semiconductor light emitting devices may have a direct current lifetime of at least 100 hours, at least 500 hours or at least 1000 hours.

Claims

7-8. -8. (canceled)

18-19. -19. (canceled)

25-44. -44. (canceled)

45. A light emitting device, comprising:

a low defect density base structure comprising;

an n-type SiC substrate; and

a GaN layer doped with n-type dopants;

a quantum well active region on the low defect density base structure that emits light at a peak output wavelength of not greater than 360 nm, the quantum well active region comprising;

a well layer comprising GaN or AlGaN; and

a doped AlGaN barrier layer;

an AlGaN layer on the quantum well active region; and

a GaN based contact layer on the AlGaN layer.

1. The light emitting device of claim 45 having a wall plug efficiency of at least 4%.

2. The light emitting device of claim 1, wherein the wall plug efficiency is at least 5%.

3. The light emitting device of claim 1, wherein the wall plug efficiency is at least 6%.

4. The light emitting device of claim 1, wherein the light emitting device has a direct current lifetime of at least 100 hours.

5. The light emitting device of claim 1, wherein the light emitting device has a direct current lifetime of at least 500 hours.

6. The light emitting device of claim 1, wherein the light emitting device has a direct current lifetime of at least 1000 hours.

9. The light emitting device of claim 1, wherein the wall plug efficiency is provided at a current density of less than about 0.35 μ

A/μ

m.

46. The light emitting device of claim 45, wherein the GaN layer doped with n-type dopants comprises a doped GaN layer having a defect density of less than about 4×

10⁸ cm<sup>−

2</sup>.

47. The light emitting device of claim 45, wherein the GaN layer doped with n-type dopants comprises GaN doped with silicon.

48. The light emitting device of claim 45, wherein the AlGaN layer on the quantum well active region comprises an AlGaN layer doped with a p-type dopant on the quantum well active region and the GaN based contact layer on the AlGaN layer comprises a GaN based contact layer doped with a p-type dopant.

49. The light emitting device of claim 48, wherein the p-type dopant comprises Mg.

50. The light emitting device of claim 45, wherein the barrier layer is doped with Si.

51. The light emitting device of claim 45, wherein the quantum well active region comprises ten quantum well layers and eleven barrier layers with the quantum well layers being disposed between adjacent barrier layers.

52. The light emitting device of claim 45, wherein the light emitting device has an overall thickness of less than about 2.5 μ

m.

53. A light emitting device, comprising:

a quantum well active region configured to emit at a peak output wavelength of not greater than 360 nm and comprising;

a barrier layer comprising Al_wIn_xGa_1-x-wN, where 0<

w≦

1, 0≦

x<

1 and 0<

w+x≦

1 and where w and x provide a barrier energy greater than a bandgap energy of GaN or within about 1 eV of the bandgap energy of GaN; and

a well layer comprising Al_yIn_zGa_1-y-zN on the barrier layer, where 0≦

y<

1, 0≦

z<

1 and 0≦

y+z<

1.

10. The light emitting device of claim 66 having a wall plug efficiency of at least 2%.

11. The light emitting device of claim 10, wherein the wall plug efficiency is at least 3%.

12. The light emitting device of claim 10, wherein the wall plug efficiency is at least 4%.

13. The light emitting device of claim 10, wherein the wall plug efficiency is provided at a current density of less than about 0.35 μ

A/μ

m².

14. The light emitting device of claim 10, wherein the wall plug efficiency is at least 6% at a current density of less than about 0.08 μ

A/μ

m².

15. The light emitting device of claim 10, wherein the light emitting device has a direct current lifetime of at least 100 hours.

16. The light emitting device of claim 10, wherein the light emitting device has a direct current lifetime of at least 500 hours.

17. The light emitting device of claim 10, wherein the light emitting device has a direct current lifetime of at least 1000 hours.

20. The light emitting device of claim 67 having a wall plug efficiency of at least 0.4%.

21. The light emitting device of claim 20, wherein the wall plug efficiency is provided at a current density of less than about 0.35 μ

A/μ

m².

22. The light emitting device of claim 20, wherein the light emitting device has a direct current lifetime of at least 100 hours.

23. The light emitting device of claim 20, wherein the light emitting device has a direct current lifetime of at least 500 hours.

24. The light emitting device of claim 20, wherein the light emitting device has a direct current lifetime of at least 1000 hours.

54. The light emitting device of claim 53, further comprising:

a first layer of Al_pGa_1-pN doped with a p-type dopant on the quantum well active region where 0<

p≦

0.8; and

a second layer of Al_qGa_1-qN doped with a p-type dopant on the first layer, where 0≦

q<

p.

55. The light emitting device of claim 53, further comprising a GaN layer doped with an n-type dopant and having a threading dislocation density of not greater than 4×

10⁸ cm<sup>−

2</sup>, the quantum well active region being disposed on the GaN layer doped with an n-type dopant.

56. The light emitting device of claim 53, further comprising a semiconductor substrate and wherein the quantum well active region is disposed on the semiconductor substrate.

57. The light emitting device of claim 56, wherein the semiconductor substrate comprises a conducting substrate.

58. The light emitting device of claim 56, wherein the semiconductor substrate comprises a SiC substrate.

59. The light emitting device of claim 56, wherein the semiconductor substrate comprises an insulating substrate.

60. The light emitting device of claim 56, wherein the semiconductor substrate comprises a sapphire substrate.

61. The light emitting device of claim 56, wherein the semiconductor substrate comprises a GaN substrate.

62. The light emitting device of claim 53, wherein the barrier layer is doped with an n-type dopant.

63. The light emitting device of claim 54, wherein the barrier layer has a thickness of from about 10 Å

to about 100 Å and

the well layer has a thickness of from about 10 Å

to about 30 Å

.

64. The light emitting device of claim 63, wherein the first layer has a thickness of about 50 Å

and the second layer has a thickness of about 300 Å

.

65. The light emitting device of claim 54, wherein the barrier layer comprises Al_wIn_xGa_1-x-wN, where 0.2<

w≦

0.8, 0≦

x<

0.2 and 0.2<

w+x≦

1 and has a thickness of from about 10 Å

to about 60 Å

;

the well layer comprises Al_yIn_zGa_1-y-zN on the barrier layer, where 0≦

y<

0.4, 0≦

z<

0.1 and 0≦

y+z<

0.5 and has a thickness of from about 10 Å

to about 30 Å

;

the first layer comprises Al_pGa_1-pN doped with a p-type dopant on the quantum well active region where 0.3<

p≦

0.8 and has a thickness of from about 50 Å

to about 250 Å

;

the second layer comprises Al_qGa_1-qN doped with a p-type dopant on the first layer, where 0≦

q<

p and the second layer has a thickness of from about 200 Å

to about 600 Å

; and

wherein the quantum well active region comprises from about 3 to about 12 quantum wells of the well layer and corresponding barrier layers.

66. The light emitting device of claim 54, wherein the barrier layer comprises Al_wIn_xGa_1-x-wN, where 0.2<

w≦

0.8, 0≦

x<

0.2 and 0.2<

w+x≦

1 and has a thickness of from about 10 Å

to about 60 Å

;

the well layer comprises Al_yIn_zGa_1-y-zN on the barrier layer, where y=0 and z=0 and has a thickness of from about 10 Å

to about 30 Å

;

the first layer comprises Al_pGa_1-pN doped with a p-type dopant on the quantum well active region where 0.3<

p≦

0.8 and has a thickness of from about 50 Å

to about 250 Å

;

the second layer comprises Al_qGa_1-qN doped with a p-type dopant on the first layer, where 0≦

q<

p and the second layer has a thickness of from about 200 Å

to about 600 Å

;

wherein the quantum well active region comprises from about 3 to about 12 quantum wells of the well layer and corresponding barrier layers; and

wherein a peak output wavelength of the light emitting device is not greater than 345 nm.

67. The light emitting device of claim 54, wherein the barrier layer comprises Al_wIn_xGa_1-x-wN, where 0.3<

w≦

0.8, 0≦

x<

0.2 and 0.3<

w+x≦

1 and has a thickness of from about 10 Å

to about 50 Å

;

the well layer comprises Al_yIn_zGa_1-y-zN on the barrier layer, where 0≦

y<

0.4, 0≦

z<

0.1 and 0≦

y+z<

0.5 and has a thickness of from about 10 Å

to about 30 Å

;

the first layer comprises Al_pGa_1-pN doped with a p-type dopant on the quantum well active region where 0.3<

p≦

0.8 and has a thickness of from about 50 Å

to about 250 Å

;

the second layer comprises Al_qGa_1-qN doped with a p-type dopant on the first layer, where 0≦

q<

p and the second layer has a thickness of from about 200 Å

to about 600 Å

;

wherein the quantum well active region comprises from about 3 to about 12 quantum wells of the well layer and corresponding barrier layers; and

wherein a peak output wavelength of the light emitting device is not greater than 330 nm.

68. The light emitting device of claim 54, wherein the well layer comprises Al_wIn_yGa_1-x-wN, where w=0, x=0 and has a thickness of 15 Å

;

the barrier layer comprises Al_yIn_zGa_1-y-zN doped with silicon on the barrier layer, where y=0.3, z=0 and has a thickness of 35 Å

;

the first layer comprises Al_pGa_1-pN doped with Mg on the quantum well active region where p=0.5 and has a thickness of 50 Å

;

the second layer comprises Al_qGa_1-qN doped with Mg on the first layer, where q=0 and the second layer has a thickness of 300 Å

;

wherein the quantum well active region comprises ten quantum wells of the well layer and corresponding barrier layers; and

wherein a peak output wavelength of the light emitting device is about 340 nm.

69. The light emitting device of claim 54, wherein the well layer comprises Al_wIn_xGa_1-x-wN, where w=0.3, x=0 and has a thickness of 15 Å

;

the barrier layer comprises Al_yIn_zGa_1-y-zN doped with silicon on the barrier layer, where y=0.5, z=0 and has a thickness of 20 Å

;

the first layer comprises Al_pGa_1-pN doped with Mg on the quantum well active region where p=0.5 and has a thickness of 230 Å

;

the second layer comprises Al_qGa_1-qN doped with Mg on the first layer, where q=0 and the second layer has a thickness of 300 Å

;

wherein the quantum well active region comprises ten quantum wells of the well layer and corresponding barrier layers; and

wherein a peak output wavelength of the light emitting device is about 325 nm.

70. A method of fabricating light emitting device, comprising:

forming a quantum well active region configured to emit at a peak output wavelength of not greater than 360 nm and comprising;

a barrier layer comprising Al_wIn_xGa_1-x-wN, where 0<

w≦

1, 0≦

x<

1 and 0<

w+x≦

1 and where w and x provide a barrier energy greater than a bandgap energy of GaN or within about 1 eV of the bandgap energy of GaN; and

a well layer comprising Al_yIn_zGa_1-y-zN on the barrier layer, where 0≦

y<

1, 0≦

z<

1 and 0≦

y+z<

1.

71. The method of claim 70, further comprising:

forming a first layer of Al_pGa_1-pN doped with a p-type dopant on the quantum well active region where 0<

p≦

0.8; and

forming a second layer of Al_qGa_1-qN doped with a p-type dopant on the first layer, where 0≦

q<

p.

72. The method of claim 70, further comprising forming a GaN layer doped with an n-type dopant and having a threading dislocation density of not greater than 4×

10⁸ cm² and wherein forming a quantum well active region comprises forming a quantum well active region on the GaN layer doped with an n-type dopant.

73. The method of claim 70, wherein forming a quantum well active region comprises forming a quantum well active region on a semiconductor substrate.

74. The method of claim 73, wherein the semiconductor substrate comprises a conducting substrate.

75. The method of claim 73, wherein the semiconductor substrate comprises a SiC substrate.

76. The method of claim 73, wherein the semiconductor substrate comprises an insulating substrate.

77. The method of claim 73, wherein the semiconductor substrate comprises a sapphire substrate.

78. The method of claim 73, wherein the semiconductor substrate comprises a GaN substrate.

79. A method of fabricating a light emitting device, comprising:

forming a low defect density base structure comprising;

an n-type SiC substrate; and

a GaN layer doped with n-type dopants;

forming a quantum well active region on the low defect density base structure that emits light at a peak output wavelength of not greater than 360 nm, the quantum well active region comprising;

a well layer comprising GaN or AlGaN; and

a doped AlGaN barrier layer;

forming an AlGaN layer on the quantum well active region; and

forming a GaN based contact layer on the AlGaN layer.

80. The method of claim 79 wherein the light emitting device has a wall plug efficiency of at least 4%.

83. The method of claim 79 wherein the light emitting device has a direct current lifetime of at least 100 hours.

84. The method of claim 79 wherein the light emitting device has an output power of at least 3 mW at a current density of about 0.35 μ

A/μ

m².

81-82. -82. (canceled)