Method of manufacturing surface textured high-efficiency radiating devices and devices obtained therefrom

• US 20030075723A1
• Filed: 10/16/2002
• Published: 04/24/2003
• Est. Priority Date: 07/28/1998
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: IMEC International, Vrije Universiteit Brussel
• Inventors: Borghs, Gustaaf, Kuijk, Maarten, Windisch, Reiner, Heremans, Paul
• Granted Patent: US 6,812,161 B2
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: G02B 6/4224 using visual alignment markings, e.g. index methods
• CPC Class Codes: G02B 6/4249 comprising arrays of active devices and fibres
• CPC Class Codes: G02B 6/4292 the light guide being disconnectable from the opto-electronic element, e.g. mutually self aligning arrangements
• CPC Class Codes: H01L 27/156 two-dimensional arrays
• CPC Class Codes: H01L 33/025 Physical imperfections, e.g. particular concentration or distribution of impurities
• CPC Class Codes: H01L 33/08 with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body H01L27/15 takes precedence
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/30 containing only elements of Group III and Group V of the Periodic Table
• CPC Class Codes: H01L 33/385 the electrode extending at least partially onto a side surface of the semiconductor body
• CPC Class Codes: H01L 33/405 Reflective materials
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector

Abstract

The present invention relates to radiation, preferably light emitting, devices with a high radiation emission efficiency and to fabricating these as small devices in an array of such devices. In one embodiment, the emitting devices can be placed in dense arrays. In another embodiment, outcoupling efficiency of the devices is improved, which leads to a reduced power consumption for a given radiation output power. In another embodiment, the speed of the radiation is increased, hence the serial bandwidth per optical channel is increased. The invention further relates to light emitting devices that exhibit uniform radiation emission characteristics.

The light emitting devices (diodes, LEDs) of the present invention can be used for applications wherein two-dimensional LED arrays, particularly low-power arrays, are useful, such as in display technology. Active matrix displays relying on liquid crystals (e.g. integrated on CMOS circuitry) could be replaced by LED arrays. Dense and bright one-dimensional LED arrays are useful for example for printing and copying.

Also for single LED applications it is important to have a maximum of photons escaping from the light emitting surface. The intensity of light per unit area (the brightness) is larger, and this is useful in many applications. Furthermore, the packaging cost can be reduced. In order to achieve a large global efficiency, many conventional LEDs need an elaborate package that includes a cavity with mirrors, because the light is emitted from more than one surface of the LED.

Claims

1. A device for emitting radiation at a predetermined wavelength, said device comprising a cavity with an active layer wherein said radiation is generated by charge carrier recombination, said cavity having a radiation confinement space including confinement features for said charge carriers, and said device comprising at least one edge having a substantially random diffraction grating structure.

2. The device as recited in claim 1, wherein the substantially random grating structure is a regular repetition of a random grating.

3. The device as recited in claim 1 further including a waveguide.

4. The device as recited in claim 3, wherein said edge having a substantially random grating structure is extending as at least one edge of said waveguide forming part of said device, and wherein said edge preferably is abutting or extending in said active layer.

5. The device as recited in claim 3 wherein said edge having a substantially random grating structure is extending as at least one edge of said waveguide forming part of said device, and wherein said edge preferably is abutting or extending in said radiation confinement space.

6. The device as recited in claim 3 wherein said edge having a substantially random grating structure is extending as at least one edge of said waveguide forming part of said device, and wherein said edge preferably is abutting or extending to said confinement features for said charge carriers.

7. The device as recited in claim 3 wherein said edge having a substantially random grating structure is extending as at least one edge of said waveguide forming part of said device, and wherein said edge preferably is abutting or extending in said cavity.

8. The device as recited in claim 1, wherein said cavity comprises at least one mesa edge for defining said radiation confinement space.

9. The device as recited in claim 1 wherein said radiation confinement space is confining said charge carriers to a subspace being smaller than the radiation confinement space within said cavity.

10. The device as recited in claim 1, having a charge carrier confinement feature made of a dielectric material.

11. The device as recited in claim 10, wherein said charge carrier confinement feature made of a dielectric material is a ring and wherein said device is mounted on a carrier substrate, said carrier substrate preferably being transparent for said radiation and more preferably including a fiber optic face plate.

12. The device as recited in claim 1, said device comprising at least two edges forming in cross-section a substantially triangular shape and the angle between said edges being smaller than 45°

and at least one of said edges having a transparent portion.

13. The device as recited in claim 12, wherein one of the two edges of said cavity is transparent for said radiation and one of the two edges is reflective and wherein the edges are at least adjacent or abutting one to another.

14. The device as recited in claim 13, wherein at least one of the two edges has a roughened surface condition.

15. An array of devices as recited in claim 1 and wherein individual devices of said array are being confined in form and functioning.

16. The array of devices as recited in claim 12 wherein individual devices of said array are being defined with a mesa edge and wherein the grooves inbetween the individual devices have a substantially random diffraction grating structure.

17. The array of devices as recited in claim 13 having a common anode and a common cathode contact.

18. The array of devices as recited in claim 12, essentially each device having a microlense thereon.

19. The array of devices as recited in claim 12 being mounted on a polymeric foil carrier.

20. The array of devices as recited in claim 16 wherein said polymeric foil further has a radiation converting phosphorous layer thereon, said device preferably emitting thereby light of a different wavelength at the carrier side of the device compared to the front-side of the device.

21. A device for emitting radiation at a predetermined wavelength, said device having a cavity with an active layer wherein said radiation is generated by charge carrier recombination, said device including a waveguide and said device comprising at least one edge having a substantially random diffraction grating structure.

22. The device as recited in claim 21, wherein the substantially random grating structure is a regular repetition of a random grating.

23. The device as recited in claim 22, wherein said edge having a substantially random grating structure is extending as at least one edge of said waveguide forming part of said device, and wherein said edge preferably is abutting or extending in said active layer.

24. The device as recited in claim 22, wherein said edge having a substantially random grating structure is extending as at least one edge of said waveguide forming part of said device, and wherein said edge preferably is abutting or extending in said radiation confinement space.

25. The device as recited in claim 22, wherein said edge having a substantially random grating structure is extending as at least one edge of said waveguide forming part of said device, and wherein said edge preferably is abutting or extending to said confinement features for said charge carriers.

26. The device as recited in claim 22, wherein said edge having a substantially random grating structure is extending as at least one edge of said waveguide forming part of said device, and wherein said edge preferably is abutting or extending in said cavity.

27. The device as recited in claim 21 wherein said cavity is having a radiation confinement space including confinement features for said charge carriers.

28. The device as recited in claim 27, wherein said cavity comprises at least one mesa edge for defining said radiation confinement space.

29. The device as recited in claim 27 wherein said radiation confinement space is confining said charge carriers to a subspace being smaller than the radiation confinement space within said cavity.

30. The device as recited in claim 29, having a charge carrier confinement feature made of a dielectric material.

31. The device as recited in claim 30, wherein said charge carrier confinement feature made of a dielectric material is a ring and wherein said device is mounted on a carrier substrate, said carrier substrate preferably being transparent for said radiation and more preferably including a fiber optic face plate.

32. The device as recited in claim 21, said device comprising at least two edges forming in cross-section a substantially triangular shape and the angle between said edges being smaller than 45°

and at least one of said edges having a transparent portion.

33. The device as recited in claim 32, wherein one of the two edges of said cavity is transparent for said radiation and one of the two edges is reflective and wherein the edges are at least adjacent or abutting one to another.

34. The device as recited in claim 33, wherein at least one of the two edges has a roughened surface condition.

35. An array of devices as recited in claim 21 and wherein individual devices of said array are being confined in form and functioning.

36. The array of devices as recited in claim 35 wherein individual devices of said array are being defined with a mesa edge and wherein the grooves inbetween the individual devices have a substantially random diffraction grating structure.

37. The array of devices as recited in claim 35 having a common anode and a common cathode contact.

38. The array of devices as recited in claim 35, essentially each device having a microlens thereon.

39. The array of devices as recited in claim 35 being mounted on a polymeric foil carrier.

40. The array of devices as recited in claim 39 wherein said polymeric foil further has a radiation converting phosphorous layer thereon, said device preferably emitting thereby light of a different wavelength at the carrier side of the device compared to the front-side of the device.

41. A device for emitting radiation at a predetermined wavelength, said device having a cavity with an active layer wherein said radiation is generated by charge carrier recombination, said device comprising at least one edge having a substantially random diffraction grating structure and being mounted on a transparent carrier.

42. A device for emitting radiation at a predetermined wavelength, said device having a cavity with an active layer wherein said radiation is generated by charge carrier recombination, said device comprising at least one edge having a substantially random diffraction grating structure and having at least one reflective edge, at least one of the electrical contacts to said device being through said reflective edge.

43. The device as recited in claim 42 being mounted on a transparent carrier.

44. A device for emitting radiation at a predetermined wavelength, said device comprising at least two edges forming in cross-section a substantially triangular shape and the angle between said edges being smaller than 45°

and at least one of said edges having a transparent portion.

45. The device as recited in claim 44, wherein one of the two edges of said cavity is transparent for said radiation and one of the two edges is reflective and wherein the edges are at least adjacent or abutting one to another.

46. The device as recited in claim 44, wherein at least one of the two edges has a roughened surface condition.

47. An array of devices for emitting radiation at a predetermined wavelength, said devices comprising a cavity with an active layer wherein said radiation is generated by charge carrier recombination, and wherein individual devices of said array are being confined in form and functioning and wherein there are waveguides between the individual devices, said waveguides having a diffraction grating structure, preferably a substantially random diffraction grating structure.

48. A method of operating a device for emitting radiation at a predetermined wavelength, said device having a cavity with an active layer wherein said radiation is generated by charge carrier recombination, said cavity having a radiation confinement space including confinement features for said charge carriers confining said charge carriers to a subspace being smaller than the radiation confinement space within said cavity.

49. The method of operating as recited in claim 48, wherein said active layer is inbetween a highly reflective edge and a transparent edge.

50. The method recited in claim 49, where at least one of said edges is roughened.

51. A method for texturing at least a part of at least one surface of a substrate, the method comprising the steps of:

applying an overlayer material covering part of said surface, said overlayer material having a pattern with substantially random distributed open features;

said step of applying said overlayer material including the substeps of applying a substantially random distribution of particles on said surface;

reducing the size of said particles; and

thereafter

etching said surface while using said particles as an etching mask, said etching mask thereby containing an substantially random masking pattern.

52. The method as recited in claim 51 further comprising the steps of:

applying a layer of a second masking material on said surface;

developing a pattern in said second masking material while reducing the size of said particles; and

thereafter

etching said surface while using said pattern as an etching mask.

53. The method as recited in claim 52, further comprising the step of removing said pattern and said particles.

54. The method as recited in claim 51, wherein said etching step is roughening said surface, said surface thereby being rendered diffusive for electromagnetic radiation impinging on said surface.

55. The method as recited in claim 51, wherein said particles are applied in a monolayer 2-dimensional partial coverage of said surface.

56. The method as recited in claim 51, wherein the applied partial coverage is about 60% of the surface.

57. The method as recited in claim 51, wherein the size reduction of the particles is yielding a coverage of about 50% of the surface.

58. The method as recited in claim 51, wherein the reduced size of said particles is in a range of 50% to 200% of the wavelength in the material of the device for said radiation.

66. The method as recited in claim 51, further comprising the step of preparing in said substrate a device for emitting radiation at a predetermined wavelength, said device having a cavity, said surface being at least a part of one of the edges of the cavity of the device.

67. The method as recited in claim 51, further comprising the step of preparing in said substrate an array of devices for emitting radiation at a predetermined wavelength, the edges of at least two devices of said array having a substantially identical random texturing pattern.

59. A method for texturing at least a part of at least one surface of a substrate, the method comprising the steps of:

applying an overlayer material of a photoresist material covering part of said surface, said overlayer material having a pattern with substantially random distributed open features; and

etching said surface while using said overlayer material as an etching mask said etching mask thereby containing a substantially random masking pattern ; and

illuminating said photoresist material with a lithography mask having a substantially random masking pattern and thereafter developing said photoresist.

60. The method as recited in claim 59, wherein said lithography mask is one of a metal mask, a direct write mask, a mask being made of metallic particles or a specular noise pattern of a coherent light source.

61. The method as recited in claim 59, wherein the etching step comprises the step of etching pillars in said substrate.

62. The method as recited in claim 59, further comprising the step of preparing in said substrate a device for emitting radiation at a predetermined wavelength, said device having a cavity, said surface being at least a part of one of the edges of the cavity of the device.

63. The method as recited in claim 59, further comprising the step of preparing in said substrate an array of devices for emitting radiation at a predetermined wavelength, the edges of at least two devices of said array having a substantially identical random texturing pattern.

64. The method as recited in claim 62, further comprising the steps of:

thinning said device or said devices of the array; and

depositing said device or said devices of the array on a carrier substrate.

65. The method as recited in claim 64, wherein said carrier substrate is transparent for said radiation and includes a fiber optic face plate.