Distributed bragg reflector for optoelectronic device

• US 20040081215A1
• Filed: 10/28/2002
• Published: 04/29/2004
• Est. Priority Date: 10/28/2002
• Status: Active Grant

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Honeywell International Inc.
• Inventors: Johnson, Ralph H., Guenter, James K., Tatum, Jimmy A., Johnson, Klein L., Biard, James R., Hawthorne, Robert A. III
• Granted Patent: US 6,990,135 B2
• Time in Patent Office: Days
• US Class Current: 372/45
• CPC Class Codes: H01S 5/18308 having a special structure for lateral current or light confinement
• CPC Class Codes: H01S 5/18313 by oxidizing at least one of the DBR layers
• CPC Class Codes: H01S 5/18333 only above the active layer
• CPC Class Codes: H01S 5/18338 Non-circular shape of the structure
• CPC Class Codes: H01S 5/2063 obtained by particle bombardment
• CPC Class Codes: H01S 5/3054 p-doping
• CPC Class Codes: H01S 5/3211 characterised by special cladding layers, e.g. details on band-discontinuities
• CPC Class Codes: H01S 5/423 having a vertical cavity

Abstract

An oxide-confined VCSELs having a distributed Bragg reflector with a heavily doped high Al content oxide aperture forming layer disposed between a low Al content first layer and a medium Al content second layer. Between the first layer and the oxide aperture forming layer there may be a thin transition region wherein the Al content changes from a higher Al content to a lower Al content. In some embodiments, the Al concentration from the oxide aperture forming layer to the second layer may occur in a step. The oxide aperture forming layer may be disposed at or near a null or a node of the electric field produced by resonant laser light. During the oxidization of the oxide aperture forming layer, all or some of the other aluminum bearing DBR layers may also become oxidized, but to a substantially lesser degree. The junction between the oxidized portion and un-oxidized portion of these layers is believed to reduce the stability and/or reliability of the device. To alleviate this, the present invention contemplates providing an implant, etch or other suitable process to reduce or eliminate one or more electrical artifacts associated with the junction between the oxidized portion and un-oxidized portion of these layers as well as reducing the oxidation of other aluminum bearing layers of the DBR.

Claims

1. A Distributed Bragg Reflector (DBR), comprising:

one or more first DBR mirror layers, each of the one or more first DBR mirror layers including an oxidized region extending from an edge of the DBR to an oxide termination edge that is situated greater than a first distance from the edge of the DBR;

one or more second DBR mirror layers, each of the one or more second DBR mirror layers including an oxidized region extending from the edge of the DBR to an oxide termination edge that is situated less than a second distance from the edge of the DBR, wherein the first distance is greater than the second distance;

at least a selected one of the first DBR mirror layers including an oxidizable material at a concentration that is above that of any of the one or more second DBR mirror layers, and is doped with an impurity at a higher level than at least some of the one or more second DBR mirror layers.

2. A Distributed Bragg Reflector according to claim 1 further comprising a transition region disposed between the selected one of the first DBR mirror layers and one of the second DBR mirror layers, wherein said transition region has a concentration of an oxidizable material that varies from a higher concentration near said selected one of the first DBR mirror layers to a lower content near the second DBR mirror layer.

3. A Distributed Bragg Reflector according to claim 1 wherein the selected one of the first DBR mirror layers is an oxide aperture forming layer.

4. A Distributed Bragg Reflector according to claim 1 wherein the first distance is greater than about two times the second distance.

5. A Distributed Bragg Reflector according to claim 1 wherein the first distance is about ten times the second distance.

6. A Distributed Bragg Reflector according to claim 1 wherein the selected one of the first DBR mirror layers that includes an oxidizable material at a concentration that is above that of any of the one or more second DBR mirror layers, is doped with the impurity at a level greater than about 1E18 atoms/cm³.

7. A Distributed Bragg Reflector according to claim 1 wherein the selected one of the first DBR mirror layers that includes an oxidizable material at a concentration that is above that of any of the one or more second DBR mirror layers, is doped with the impurity at a level greater than about 5E18 atoms/cm³.

8. A distributed Bragg reflector;

comprising;

a first layer including an oxidizable material at a first concentration;

a second layer including an oxidizable material at a second concentration;

an oxide aperture forming layer including an oxidizable material at a third concentration, wherein the first concentration is less than the second concentration and the second concentration is less than the third concentration, and wherein said oxide aperture forming layer is disposed between said first layer and said second layer; and

a transition region disposed between said oxide aperture forming layer and said first layer, wherein said transition region includes an oxidizable material at a concentration that varies from a higher concentration near said oxide aperture forming layer to a lower concentration near said first layer.

9. A distributed Bragg reflector according to claim 8, wherein the first concentration is at or below 50%.

10. A distributed Bragg reflector according to claim 8, wherein the second concentration is at or below 90%.

11. A distributed Bragg reflector according to claim 8, wherein the second concentration is at or below 80%.

12. A distributed Bragg reflector according to claim 8, wherein the third concentration is at or above 95%.

13. A distributed Bragg reflector according to claim 8, wherein the transition region abuts the oxide aperture forming layer and the first layer.

14. A distributed Bragg reflector according to claim 8, wherein the oxide aperture forming layer abuts the second layer.

15. A distributed Bragg reflector according to claim 8, wherein the oxide aperture forming layer is doped with an impurity at a higher level than either the first layer or second layer.

16. A distributed Bragg reflector according to claim 8, wherein said transition region is about 20 nm wide.

17. A distributed Bragg reflector according to claim 8 further comprising another transition region disposed between said oxide aperture forming layer and said second layer, wherein said transition region includes an oxidizable material at a concentration that varies from a higher concentration near said oxide aperture forming layer to a lower concentration near said second layer.

18. A distributed Bragg reflector according to claim 8, wherein the oxidizable material includes aluminum.

25. A vertical cavity surface emitting laser according to claim 16, wherein said Al content of said transition region varies substantially linearly.

26. A vertical cavity surface emitting laser according to claim 16, wherein said Al content of said transition region varies substantially non-linearly.

27. A vertical cavity surface emitting laser according to claim 16, wherein said transition region is doped with an acceptor concentration that varies from a higher concentration near said oxide aperture forming layer to a lower concentration near said first layer.

28. A vertical cavity surface emitting laser according to claim 16, wherein said oxide aperture forming layer is doped with an impurity more heavily than the first layer and second layer.

29. A vertical cavity surface emitting laser according to claim 16, wherein said oxide aperture forming layer is disposed at or near the null of an electric field produced by resonant laser light.

19. A vertical cavity surface emitting laser, comprising:

an active region for emitting light at a predetermined wavelength in response to an applied electric current;

a first distributed Bragg reflector mirror situated adjacent one side of the active region, said first distributed Bragg reflector mirror for reflecting light emitted by said active region back toward said active region;

a second distributed Bragg reflector mirror situated adjacent the opposite side of said active region, said second distributed Bragg reflector mirror for reflecting light emitted by said active region back toward said active region;

wherein said second distributed Bragg reflector mirror includes;

a first layer having an Al content below about 35%;

a second layer having an Al content between about 70% and 90%;

an oxide aperture forming layer having an Al content greater than about 95%;

wherein said oxide aperture forming layer is disposed between said first layer and said second layer; and

a transition region disposed between said oxide aperture forming layer and said first layer, wherein said transition region has an Al content that varies from a higher Al content near said oxide aperture forming layer to a lower Al content near said first layer.

20. A vertical cavity surface emitting laser according to claim 19, wherein said oxide aperture forming layer has an Al content of about 98%.

21. A vertical cavity surface emitting laser according to claim 19, wherein said first layer has an Al content between 12% and 18%.

22. A vertical cavity surface emitting laser according to claim 19, wherein said second layer has an Al content near 65%.

23. A vertical cavity surface emitting laser according to claim 19, wherein said transition region is between about 10 and 100 nm thick.

24. A vertical cavity surface emitting laser according to claim 23, wherein said transition region is about 20 nm thick.

30. A method for forming a distributed Bragg reflector;

the method comprising the steps of;

providing a first layer including an oxidizable material at a first concentration;

providing a second layer including an oxidizable material at a second concentration;

providing an oxide aperture forming layer including an oxidizable material at a third concentration, wherein the first concentration is less than the second concentration and the second concentration is less than the third concentration, and wherein said oxide aperture forming layer is disposed between said first layer and said second layer; and

providing a transition region disposed between said oxide aperture forming layer and said first layer, wherein said transition region includes an oxidizable material at a concentration that varies from a higher concentration near said oxide aperture forming layer to a lower concentration near said first layer.

31. A Distributed Bragg Reflector (DBR) having an edge, comprising:

one or more first DBR mirror layers, each of the one or more first DBR mirror layers including an oxidized region extending from the edge of the DBR to an oxide termination edge that is situated greater than a first distance from the edge of the DBR;

one or more second DBR mirror layers, each of the one or more second DBR mirror layers including an oxidized region extending from the edge of the DBR to an oxide termination edge that is situated less than a second distance from the edge of the DBR, wherein the first distance is greater than the second distance;

means for reducing or eliminating one or more electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers;

at least a selected one of the first DBR mirror layers being including an oxidizable material at a concentration that is above that of any of the one or more second DBR mirror layers, and is doped with an impurity at a higher level than any of the one or more second DBR mirror layers.

32. A Distributed Bragg Reflector according to claim 31 further comprising a transition region disposed between the selected one of the first DBR mirror layers and one of the second DBR mirror layers, wherein said transition region has a concentration of an oxidizable material that varies from a higher concentration near said selected one of the first DBR mirror layers to a lower content near the second DBR mirror layer.

33. A Distributed Bragg Reflector according to claim 31 wherein said selected one of the first DBR mirror layers is disposed at or near an expected null of an electric field produced by resonant laser light.

34. A Distributed Bragg Reflector (DBR) having an edge, comprising:

one or more first DBR mirror layers, each of the one or more first DBR mirror layers including an oxidized region extending from the edge of the DBR to an oxide termination edge that is situated greater than a first distance from the edge of the DBR;

one or more second DBR mirror layers, each of the one or more second DBR mirror layers including an oxidized region extending from the edge of the DBR to an oxide termination edge that is situated less than a second distance from the edge of the DBR, wherein the first distance is greater than the second distance;

means for reducing or eliminating one or more electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers;

a first one of the one or more second DBR mirror layers having a first concentration of an oxidizable material;

a second one of the second DBR mirror layers having a second concentration of an oxidizable material;

a selected one of the one or more first DBR mirror layers having a third concentration of an oxidizable material, wherein the selected one of the one or more first DBR mirror layers is disposed between said first one of the second DBR mirror layers and said second one of the second DBR mirror layers, and wherein the first concentration of the oxidizable material is less than the second concentration of the oxidizable material, and the second concentration of the oxidizable material is below the third concentration of the oxidizable material; and

a transition region disposed between said selected one of the one or more first DBR mirror layers and said first one of the second DBR mirror layers, wherein said transition region has a concentration of an oxidizable material that varies from a higher content near said selected one of the one or more first DBR mirror layers to a lower content near said first one of the second DBR mirror layers.

35. A Distributed Bragg Reflector according to claim 34 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that crosses the oxide termination edge of at least some of the one or more second DBR mirror layers.

36. A Distributed Bragg Reflector according to claim 34 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that extends from the edge of the DBR past the second distance.

37. A Distributed Bragg Reflector according to claim 34 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that extends from the edge of the DBR past the second distance but not all the way to the first distance.

38. A Distributed Bragg Reflector according to claim 34 wherein the implant is a proton implant.

39. A Distributed Bragg Reflector according to claim 34 wherein the implant includes an electrically active impurity.

40. A Distributed Bragg Reflector according to claim 34 wherein the means for reducing or eliminating selected electrical affects of the oxide termination edge of the one or more second DBR mirror layers includes removing a portion of the one or more second DBR mirror layers that includes the oxide termination edge of the one or more second DBR mirror layers.

41. A Distributed Bragg Reflector according to claim 34 wherein the means for reducing or eliminating selected electrical effects of the oxide termination edge of the one or more second DBR mirror layers includes an implant that resides entirely between the first distance and the second distance.

42. A Distributed Bragg Reflector according to claim 34 wherein said transition region has a concentration of oxidizable material that is graded from substantially that of said selected one of the one or more first DBR mirror layers near said selected one of the one or more first DBR mirror layers to substantially that of said first one of the second DBR mirror layers near said first one of the second DBR mirror layers.

43. A Distributed Bragg Reflector according to claim 42 wherein said second layer of the second DBR mirror layers abuts the said selected one of the one or more first DBR mirror layers.

44. A Distributed Bragg Reflector according to claim 43 wherein said transition region abuts the said selected one of the one or more first DBR mirror layers.

45. A Distributed Bragg Reflector according to claim 44 wherein said first layer of the second DBR mirror layers abuts the said transition region.

46. A Distributed Bragg Reflector according to claim 34 wherein said selected one of the one or more first DBR mirror layers is heavily doped with an impurity.

47. A Distributed Bragg Reflector according to claim 34 wherein said oxidizable material is aluminum (Al).

48. A Distributed Bragg Reflector according to claim 47, wherein said selected one of the one or more first DBR mirror layers has an Al concentration greater than 95%.

49. A Distributed Bragg Reflector according to claim 48, wherein said first one of the one or more second DBR mirror layers has an Al concentration below 35%.

50. A Distributed Bragg Reflector according to claim 49, wherein said second one of the one or more second DBR mirror layers has an Al concentration below 85%.

51. A Distributed Bragg Reflector according to claim 34, wherein said transition region is about 20 nm thick.

52. A Distributed Bragg Reflector according to claim 34, wherein said transition region has a concentration of an oxidizable material that varies substantially linearly from a higher content near said selected one of the one or more first DBR mirror layers to a lower content near said first one of the second DBR mirror layers.

53. A Distributed Bragg Reflector according to claim 34 wherein said selected one of the first DBR mirror layers is disposed at or near an expected null of an electric field produced by resonant laser light.

54. A Vertical Cavity Surface Emitting Laser (VCSEL), comprising:

an active region for emitting light at a predetermined wavelength in response to an applied electric current;

a first distributed Bragg reflector mirror situated on one side of said active region, said first distributed Bragg reflector mirror for reflecting light emitted by said active region back toward said active region;

a second distributed Bragg reflector mirror situated on an opposite side of said active region, said second distributed Bragg reflector mirror for reflecting light emitted by said active region back toward said active region, the second distributed Bragg reflector mirror having a side edge;

wherein said second distributed Bragg reflector mirror includes;

one or more first DBR mirror layers, each of the one or more first DBR mirror layers including an oxidized region extending from the side edge of the second DBR to an oxide termination edge that is situated greater than a first distance from the side edge of the second DBR;

one or more second DBR mirror layers, each of the one or more second DBR mirror layers including an oxidized region extending from the side edge of the second DBR to an oxide termination edge that is situated less than a second distance from the side edge of the second DBR, wherein the first distance is greater than the second distance;

means for reducing or eliminating one or more electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers;

a first one of the one or more second DBR mirror layers having a first concentration of an oxidizable material;

a second one of the second DBR mirror layers having a second concentration of an oxidizable material; and

a selected one of the one or more first DBR mirror layers having a third concentration of an oxidizable material, wherein the selected one of the one or more first DBR mirror layers is disposed between said first one of the second DBR mirror layers and said second one of the second DBR mirror layers, and wherein the first concentration of the oxidizable material is less than the second concentration of the oxidizable material, and the second concentration of the oxidizable material is below the third concentration of the oxidizable material.

55. Vertical Cavity Surface Emitting Laser (VCSEL) according to claim 54 further comprising:

a transition region disposed between said selected one of the one or more first DBR mirror layers and said first one of the second DBR mirror layers, wherein said transition region has a concentration of an oxidizable material that varies from a higher content near said selected one of the one or more first DBR mirror layers to a lower content near said first one of the second DBR mirror layers.

56. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that crosses the oxide termination edge of at least some of the one or more second DBR mirror layers.

57. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that extends from the edge of the DBR past the second distance.

58. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein said implant does not extend all the way to the first distance.

59. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that at least partially electrically isolates the oxide termination edge of at least some of the one or more second DBR mirror layers from a region of the one or more second DBR mirror layers that resides inside the first distance.

60. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that extends down through the active region.

61. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein said side edge of the second distributed Bragg reflector mirror does not extend down into the active region.

62. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes a proton implant.

63. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant of an electrically active impurity.

64. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes a helium implant.

65. A Vertical Cavity Surface Emitting Laser according to claim 54 wherein the means for reducing or eliminating selected electrical affects of the oxide termination edge of the one or more second DBR mirror layers includes removing a portion of the one or more second DBR mirror layers that includes the oxide termination edge of the one or more second DBR mirror layers.

66. A Distributed Bragg Reflector according to claim 54 wherein said selected one of the first DBR mirror layers is disposed at or near an expected null of an electric field produced by resonant laser light of the Vertical Cavity Surface Emitting Laser.

67. A method for forming a Distributed Bragg Reflector (DBR), comprising:

providing a number of DBR mirror layers with an edge;

wherein one or more first DBR mirror layers each include an oxidized region extending from the edge of the DBR to an oxide termination edge that is situated greater than a first distance from the edge of the DBR;

and wherein one or more second DBR mirror layers each include an oxidized region extending from the edge of the DBR to an oxide termination edge that is situated less than a second distance from the edge of the DBR, wherein the first distance is greater than the second distance;

and wherein a first one of the one or more second DBR mirror layers include a first concentration of an oxidizable material, and a second one of the second DBR mirror layers include a second concentration of an oxidizable material;

and wherein a selected one of the one or more first DBR mirror layers include a third concentration of an oxidizable material, wherein the selected one of the one or more first DBR mirror layers is disposed between said first one of the second DBR mirror layers and said second one of the second DBR mirror layers, and wherein the first concentration of the oxidizable material is less than the second concentration of the oxidizable material, and the second concentration of the oxidizable material is below the third concentration of the oxidizable material;

providing a transition region disposed between said selected one of the one or more first DBR mirror layers and said first one of the second DBR mirror layers, wherein said transition region has a concentration of an oxidizable material that varies from a higher content near said selected one of the one or more first DBR mirror layers to a lower content near said first one of the second DBR mirror layers; and

reducing or eliminating one or more electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers.

68. A method according to claim 67 wherein said reducing or elimination step includes providing an implant that crosses the oxide termination edge of at least some of the one or more second DBR mirror layers.

69. A method according to claim 67 wherein said reducing or elimination step includes providing an implant that extends from the edge of the DBR past the second distance.

70. A method according to claim 67 wherein said reducing or elimination step includes providing an implant that extends from the edge of the DBR past the second distance but not all the way to the first distance.

71. A method according to claim 67 wherein said reducing or elimination step includes etching a portion of the one or more second DBR mirror layers that includes the oxide termination edge of the one or more second DBR mirror layers.

72. A method according to claim 67 wherein said step of reducing or eliminating one or more electrical artifacts comprises the step of increasing the resistivity of a selected portion of a selected number of the one or more second DBR mirror layers, the selected portion including a region that is situated greater than the second distance from the edge of the DBR.

73. A method according to claim 67 wherein said step of reducing or eliminating one or more electrical artifacts comprises the step of increasing the resistivity of a selected portion of a selected number of the one or more second DBR mirror layers in and around the oxide termination edge of at least some of the one or more second DBR mirror layers.

74. A method for isolating adjacent optoelectronic devices fabricated on a wafer, the wafer having a bottom mirror, an active region and a top mirror, the method comprising the steps of:

etching one or more relief etch regions--into at least the top mirror of the wafer between adjacent optoelectronic devices; and

providing an implant into at least some of the relief etch regions.