Title:
Methods of forming electronic devices including semiconductor mesa structures and conductivity junctions and related devices
Kind Code:
A1


Abstract:
An electronic device may include a substrate and a semiconductor mesa on the substrate. More particularly, the semiconductor mesa may have a mesa base adjacent the substrate, a mesa surface opposite the substrate, and mesa sidewalls between the mesa surface and the mesa base. In addition, the semiconductor mesa may have a first conductivity type between the mesa base and a junction, the junction may be between the mesa base and the mesa surface, and the semiconductor mesa may have a second conductivity type between the junction and the mesa surface. Related methods are also discussed.



Inventors:
Bergman, Michael John (Chapel Hill, NC, US)
Emerson, David Todd (Chapel Hill, NC, US)
Abare, Amber Christine (Cary, NC, US)
Haberern, Kevin Ward (Cary, NC, US)
Application Number:
10/742426
Publication Date:
08/05/2004
Filing Date:
12/19/2003
Assignee:
BERGMAN MICHAEL JOHN
EMERSON DAVID TODD
ABARE AMBER CHRISTINE
HABERERN KEVIN WARD
Primary Class:
International Classes:
C30B1/00; H01L21/00; H01L33/14; H01S5/042; H01S5/22; H01S5/223; H01S5/323; H01S5/227; (IPC1-7): H01L33/00
View Patent Images:



Primary Examiner:
NADAV, ORI
Attorney, Agent or Firm:
MYERS BIGEL, P.A. (PO BOX 37428, RALEIGH, NC, 27627, US)
Claims:

That which is claimed is:



1. A light emitting device comprising: a silicon carbide substrate; and a semiconductor structure on the substrate, the semiconductor structure including a mesa having a mesa base adjacent the substrate, a mesa surface opposite the substrate, and mesa sidewalls between the mesa surface and the mesa base, wherein the semiconductor structure has a first conductivity type adjacent the silicon carbide substrate, wherein the semiconductor structure has a second conductivity type adjacent the mesa surface, wherein the semiconductor structure has a junction between the first and second conductivity types, and wherein the mesa is configured to provide at least one of current confinement or optical confinement for a light emitting device in the semiconductor structure.

2. A light emitting device according to claim 1 wherein the junction is between the mesa base and the mesa surface.

3. A light emitting device according to claim 2 wherein the junction is no more than approximately 5 microns from the mesa base.

4. A light emitting device according to claim 2 wherein the junction is no more than approximately 0.75 microns from the mesa base.

5. A light emitting device according to claim 2 wherein the junction is at least approximately 0.05 microns from the mesa base.

6. A light emitting device according to claim 5 wherein the junction is at least approximately 0.1 microns from the mesa base.

7. A light emitting device according to claim 1 wherein the semiconductor structure includes a semiconductor base layer between the mesa base and the silicon carbide substrate wherein the junction is between a surface of the base layer opposite the silicon carbide substrate and the silicon carbide substrate.

8. A light emitting device according to claim 7 wherein the junction is no more than approximately 0.4 microns from the surface of the base layer opposite the silicon carbide substrate.

9. A light emitting device according to claim 8 wherein the junction is no more than approximately 0.2 microns from the surface of the base layer opposite the substrate.

10. A light emitting device according to claim 7 wherein the junction is at least approximately 0.05 microns from the surface of the base layer opposite the substrate.

11. A light emitting device according to claim 10 wherein the junction is at least approximately 0.1 microns from the surface of the base layer opposite the substrate.

12. A light emitting device according to claim 1 wherein the semiconductor structure comprises a Group III-V semiconductor material.

13. A method of forming a light emitting device, the method comprising: forming a silicon carbide substrate; and forming a semiconductor structure on the substrate, the semiconductor structure including a mesa having a mesa base adjacent the substrate, a mesa surface opposite the substrate, and mesa sidewalls between the mesa surface and the mesa base, wherein the semiconductor structure has a first conductivity type adjacent the silicon carbide substrate, wherein the semiconductor structure has a second conductivity type adjacent the mesa surface, wherein the semiconductor structure has a junction between the first and second conductivity types, and wherein the mesa is configured to provide at least one of current confinement or optical confinement for a light emitting device in the semiconductor structure.

14. A method according to claim 13 wherein the junction is between the mesa base and the mesa surface.

15. A method according to claim 14 wherein the junction is no more than approximately 5 microns from the mesa base.

16. A method according to claim 14 wherein the junction is no more than approximately 0.75 microns from the mesa base.

17. A method according to claim 14 wherein the junction is at least approximately 0.05 microns from the mesa base.

18. A method according to claim 17 wherein the junction is at least approximately 0.1 microns from the mesa base.

19. A method according to claim 13 wherein the semiconductor structure includes a semiconductor base layer between the mesa base and the silicon carbide substrate wherein the junction is between a surface of the base layer opposite the silicon carbide substrate and the silicon carbide substrate.

20. A method according to claim 19 wherein the junction is no more than approximately 0.4 microns from the surface of the base layer opposite the silicon carbide substrate.

21. A method according to claim 20 wherein the junction is no more than approximately 0.2 microns from the surface of the base layer opposite the substrate.

22. A method according to claim 19 wherein the junction is at least approximately 0.05 microns from the surface of the base layer opposite the substrate.

23. A method according to claim 22 wherein the junction is at least approximately 0.1 microns from the surface of the base layer opposite the substrate.

24. A method according to claim 13 wherein the semiconductor structure comprises a Group III-V semiconductor material.

25. An electronic device comprising: a substrate; and a semiconductor mesa on the substrate, the semiconductor mesa having a mesa base adjacent the substrate, a mesa surface opposite the substrate, and mesa sidewalls between the mesa surface and the mesa base, wherein the semiconductor mesa has a first conductivity type between the mesa base and a junction, wherein the junction is between the mesa base and the mesa surface, and wherein the semiconductor mesa has a second conductivity type between the junction and the mesa surface.

26. An electronic device according to claim 25 wherein the semiconductor mesa is configured to provide at least one of optical confinement or current confinement for a light emitting device in the semiconductor mesa.

27. An electronic device according to claim 25 wherein the substrate comprises a silicon carbide substrate.

28. An electronic device according to claim 25 wherein the junction comprises a physical location where doping of the second conductivity type begins.

29. An electronic device according to claim 25 wherein the first conductivity type comprises N-type and wherein the second conductivity type comprises P-type.

30. An electronic device according to claim 25 wherein the semiconductor mesa comprises a Group III-V semiconductor material.

31. An electronic device according to claim 30 wherein the semiconductor mesa comprises a Group III-nitride semiconductor material.

32. An electronic device according to claim 25 wherein the junction is no more that approximately 5 microns from the mesa base.

33. An electronic device according to claim 32 wherein the junction is no more than approximately 0.75 microns from the mesa base.

34. An electronic device according to claim 25 wherein the junction is at least 0.05 microns from the mesa base.

35. An electronic device according to claim 34 wherein the junction is at least 0.1 microns from the mesa base.

36. An electronic device according to claim 25 wherein the semiconductor mesa has a thickness in the range of approximately 0.1 microns to 5 microns.

37. An electronic device according to claim 25 further comprising: a semiconductor base layer between the substrate and the semiconductor mesa, wherein the semiconductor base layer has the first conductivity type throughout.

38. An electronic device according to claim 37 wherein the semiconductor base layer has a thickness no greater than approximately 5 microns.

39. An electronic device according to claim 37 wherein each of the semiconductor base layer and the semiconductor mesa comprise a Group III-V semiconductor material.

40. An electronic device according to claim 25 wherein the substrate comprises a conductive material.

41. An electronic device according to claim 40 wherein the substrate comprises a conductive semiconductor material.

42. An electronic device according to claim 41 wherein the conductive semiconductor material comprises at least one of gallium nitride and/or silicon carbide.

43. An electronic device comprising: a substrate; a semiconductor base layer on the substrate, wherein the semiconductor base layer has a first conductivity type between the substrate and a junction, wherein the junction is between the substrate and a surface of the base layer opposite the substrate, and wherein the semiconductor base layer has a second conductivity type between the junction and the surface of the base layer opposite the substrate; and a semiconductor mesa on the surface of the base layer opposite the substrate, the semiconductor mesa having a mesa surface opposite the semiconductor base layer and mesa sidewalls between the mesa surface and the base layer, wherein the semiconductor mesa has the second conductivity type throughout.

44. An electronic device according to claim 43 wherein the semiconductor mesa is configured to provide at least one of optical confinement or current confinement for a light emitting device in the semiconductor base layer and semiconductor mesa.

45. An electronic device according to claim 43 wherein the substrate comprises a silicon carbide substrate.

46. An electronic device according to claim 43 wherein the junction comprises a physical location where doping of the second conductivity type begins.

47. An electronic device according to claim 43 wherein the first conductivity type comprises N-type and wherein the second conductivity type comprises P-type.

48. An electronic device according to claim 43 wherein each of the semiconductor mesa and the semiconductor base layer comprises a Group III-V semiconductor material.

49. An electronic device according to claim 43 wherein each of the semiconductor mesa and the semiconductor base layer comprises a Group III-nitride semiconductor material.

50. An electronic device according to claim 43 wherein the junction is no more that approximately 0.4 microns from the surface of the base layer opposite the substrate.

51. An electronic device according to claim 43 wherein the junction is no more than approximately 0.2 microns from the surface of the base layer opposite the substrate.

52. An electronic device according to claim 43 wherein the junction is at least approximately 0.05 microns from the surface of the base layer opposite the substrate.

53. An electronic device according to claim 52 wherein the junction is at least approximately 0.1 microns from the surface of the base layer opposite the substrate.

54. An electronic device according to claim 43 wherein the semiconductor mesa has a thickness in the range of approximately 0.1 microns to 5 microns.

55. An electronic device according to claim 43 wherein the semiconductor base layer has a thickness no greater than approximately 5 microns.

56. An electronic device according to claim 43 wherein the substrate comprises a conductive material.

57. An electronic device according to claim 56 wherein the substrate comprises a conductive semiconductor material.

58. An electronic device according to claim 57 wherein the conductive semiconductor material comprises at least one of gallium nitride and/or silicon carbide.

59. A method of forming an electronic device, the method comprising: forming a semiconductor mesa on a substrate, the semiconductor mesa having a mesa base adjacent the substrate, a mesa surface opposite the substrate, and mesa sidewalls between the mesa surface and the mesa base, wherein the semiconductor mesa has a first conductivity type between the mesa base and a junction, wherein the junction is between the mesa base and the mesa surface, and wherein the semiconductor mesa has a second conductivity type between the junction and the mesa surface.

60. A method according to claim 59 wherein the semiconductor mesa is configured to provide at least one of optical confinement or current confinement for a light emitting device in the semiconductor mesa.

61. A method according to claim 59 wherein the substrate comprises a silicon carbide substrate.

62. A method according to claim 59 wherein the junction comprises a physical location where doping of the second conductivity type begins.

63. A method according to claim 59 wherein the first conductivity type comprises N-type and wherein the second conductivity type comprises P-type.

64. A method according to claim 59 wherein the semiconductor mesa comprises a Group III-V semiconductor material.

65. A method according to claim 64 wherein the semiconductor mesa comprises a Group III-nitride semiconductor material.

66. A method according to claim 59 wherein the junction is no more that approximately 5 microns from the mesa base.

67. A method according to claim 59 wherein the junction is no more than approximately 0.75 microns from the mesa base.

68. A method according to claim 59 wherein the junction is at least 0.05 microns from the mesa base.

69. A method according to claim 63 wherein the junction is at least 0.1 microns from the mesa base.

70. A method according to claim 59 wherein the semiconductor mesa has a thickness in the range of approximately 0.1 microns to 5 microns.

71. A method according to claim 59 wherein forming the semiconductor mesa comprises forming a layer of a semiconductor material on the substrate, forming a mask on the layer of the semiconductor material, and etching portions of layer of the semiconductor material exposed by the mask wherein a depth of etching defines a thickness of the mesa.

72. A method according to claim 59 further comprising: forming a semiconductor base layer between the substrate and the semiconductor mesa, wherein the semiconductor base layer has the first conductivity type throughout.

73. A method according to claim 72 wherein forming the semiconductor mesa and forming the semiconductor base layer comprise forming a layer of a semiconductor material on the substrate, forming a mask on the layer of the semiconductor material, and etching portions of layer of the semiconductor material exposed by the mask wherein a depth of etching defines a thickness of the mesa.

74. A method according to claim 73 wherein the layer of the semiconductor material includes a junction at a junction depth and wherein the depth of etching of the layer of the semiconductor material is greater than the junction depth.

75. A method according to claim 72 wherein the semiconductor. base layer has a thickness no greater than approximately 5 microns.

76. A method according to claim 72 wherein each of the semiconductor base layer and the semiconductor mesa comprise a Group III-V semiconductor material.

77. A method according to claim 59 wherein the substrate comprises silicon carbide.

78. A method of forming an electronic device, the method comprising: forming a semiconductor base layer on a substrate, wherein the semiconductor base layer has a first conductivity type between the substrate and a junction, wherein the junction is between the substrate and a surface of the base layer opposite the substrate, and wherein the semiconductor base layer has a second conductivity type between the junction and the surface of the base layer opposite the substrate; and forming a semiconductor mesa on the surface of the base layer opposite the substrate, the semiconductor mesa having a mesa surface opposite the semiconductor base layer and mesa sidewalls between the mesa surface and the base layer, wherein the semiconductor mesa has the second conductivity type throughout.

79. A method according to claim 78 wherein the semiconductor mesa is configured to provide at least one of optical confinement or current confinement for a light emitting device in the semiconductor base layer and semiconductor mesa.

80. A method according to claim 78 wherein the. substrate comprises a silicon carbide substrate.

81. A method according to claim 78 wherein the junction comprises a physical location where doping of the second conductivity type begins.

82. A method according to claim 78 wherein the first conductivity type comprises N-type and wherein the second conductivity type comprises P-type.

83. A method according to claim 78 wherein each of the semiconductor mesa and the semiconductor base layer comprises a Group III-V semiconductor material.

84. A method according to claim 83 wherein each of the semiconductor mesa and the semiconductor base layer comprises a Group III-nitride semiconductor material.

85. A method according to claim 78 wherein the junction is no more that approximately 0.4 microns from the surface of the base layer opposite the substrate.

86. A method according to claim 78 wherein the junction is no more than approximately 0.2 microns from the surface of the base layer opposite the substrate.

87. A method according to claim 78 wherein the junction is at least approximately 0.05 microns from the surface of the base layer opposite the substrate.

88. A method according to claim 87 wherein the junction is at least approximately 0.1 microns from the surface of the base layer opposite the substrate.

89. A method according to claim 78 wherein the semiconductor mesa has a thickness in the range of approximately 0.1 microns to 5 microns.

90. A method according to claim 78 wherein the semiconductor base layer has a thickness no greater than approximately 5 microns.

91. A method according to claim 78 wherein the substrate comprises silicon carbide.

92. A method according to claim 78 wherein forming the semiconductor mesa and forming the semiconductor base layer comprise forming a layer of a semiconductor material on the substrate, forming a mask on the layer of the semiconductor material, and etching portions of layer of the semiconductor material exposed by the mask wherein a depth of etching defines a thickness of the mesa.

93. A method according to claim 92 wherein the layer of the semiconductor material includes a junction at a junction depth and wherein the depth of etching of the layer of the semiconductor material is less than the junction depth.

Description:

RELATED APPLICATIONS

[0001] The present application claims the benefit of, U.S. Provisional Application No. 60/435,213 filed Dec. 20, 2002, and entitled “Laser Diode With Self-Aligned Index Guide And Via”; U.S. Provisional Application No. 60/434,914 filed Dec. 20, 2002, and entitled “Laser Diode With Surface Depressed Ridge Waveguide”; U.S. Provisional Application No. 60/434,999 filed Dec. 20, 2002 and entitled “Laser Diode with Etched Mesa Structure”; and U.S. Provisional Application No. 60/435,211 filed Dec. 20, 2002, and entitled “Laser Diode With Metal Current Spreading Layer.” The disclosures of each of these provisional applications are hereby incorporated herein in their entirety by reference.

[0002] The present application is also related to: U.S. Application No. ______ (Attorney Docket No. 5308-281) entitled “Methods Of Forming Semiconductor Devices Having Self Aligned Semiconductor Mesas and Contact Layers And Related Devices” filed concurrently herewith; U.S. Application No. ______ (Attorney Docket No. 5308-282) entitled “Methods Of Forming Semiconductor Devices Including Mesa Structures And Multiple Passivation Layers And Related Devices” filed concurrently herewith; and U.S. Application No. ______ (Attorney Docket No. 5308-280) entitled “Methods Of Forming Semiconductor Mesa Structures Including Self-Aligned Contact Layers And Related Devices” filed concurrently herewith. The disclosures of each of these U.S. Applications are hereby incorporated herein in their entirety by reference.

FIELD OF THE INVENTION

[0003] The present invention relates to the field of electronics, and more particularly, to methods of forming electronic. semiconductor devices and related structures.

BACKGROUND OF THE INVENTION

[0004] A laser is a device that produces a beam of coherent monochromatic light as a result of stimulated emission of photons. Stimulated emission of photons may also produce optical gain, which may cause light beams produced by lasers to have a high optical energy. A number of materials are capable of producing the lasing effect and include certain high-purity crystals (ruby is a common example), semiconductors, certain types of glass, certain gases including carbon dioxide, helium, argon and neon, and certain plasmas.

[0005] More recently, lasers have been developed in semiconducting materials, thus taking advantage of the smaller size, lower cost and other related advantages typically associated with semiconductor devices. In the semiconductor arts, devices in which photons play a major role are referred to as “photonic” or “optoelectronic” devices. In turn, photonic devices include light-emitting diodes (LEDs), photodetectors, photovoltaic devices, and semiconductor lasers.

[0006] Semiconductor lasers are similar to other lasers in that the emitted radiation has spatial and temporal coherence. As noted above, laser radiation is highly monochromatic (i.e., of narrow band width) and it produces highly directional beams of light. Semiconductor lasers may differ, however, from other lasers in several respects. For example, in semiconductor lasers, the quantum transitions are associated with the band properties of materials; semiconductor lasers may be very compact in size, may have very narrow active regions, and larger divergence of the laser beam; the characteristics of a semiconductor laser may be strongly influenced by the properties of the junction medium; and for P-N junction lasers, the lasing action is produced by passing a forward current through the diode itself. Overall, semiconductor lasers can provide very efficient systems that may be controlled by modulating the current directed across the devices. Additionally, because semiconductor lasers can have very short photon lifetimes, they may be used to produce high-frequency modulation. In turn, the compact size and capability for such high-frequency modulation may make semiconductor lasers an important light source for optical fiber communications.

[0007] In broad terms, the structure of a semiconductor laser should provide optical confinement to create a resonant cavity in which light amplification may occur, and electrical confinement to produce high current densities to cause stimulated emission to occur. Additionally, to produce the laser effect (stimulated emission of radiation), the semiconductor may be a direct bandgap material rather than an indirect bandgap material. As known to those familiar with semiconductor characteristics, a direct bandgap material is one in which an electron's transition from the valence band to the conduction band does not require a change in crystal momentum for the electron. Gallium arsenide and gallium nitride are examples of direct bandgap semiconductors. In indirect bandgap semiconductors, the alternative situation exists; i.e., a change of crystal momentum is required for an electron's transition between the valence and conduction bands. Silicon and silicon carbide are examples of such indirect semiconductors.

[0008] A useful explanation of the theory, structure and operation of semiconductor lasers, including optical and electronic confinement and mirroring, is given by Sze, Physics of Semiconductor Devices, 2nd Edition (1981) at pages 704-742, and these pages are incorporated entirely herein by reference.

[0009] As known to those familiar with photonic devices such as LEDs and lasers, the frequency of electromagnetic radiation (i.e., the photons) that can be produced by a given semiconductor material may be a function of the material's bandgap. Smaller bandgaps produce lower energy, longer wavelength photons, while wider bandgap materials produce higher energy, shorter wavelength photons. For example, one semiconductor commonly used for lasers is aluminum indium gallium phosphide (AlInGaP). Because of this material's bandgap (actually a range of bandgaps depending upon the mole or atomic fraction of each element present), the light that AlInGaP can produce may be limited to the red portion of the visible spectrum, i.e., about 600 to 700 nanometers (nm). In order to produce photons that have wavelengths in the blue or ultraviolet portions of the spectrum, semiconductor materials having relatively large bandgaps may be used. Group III-nitride materials such as gallium nitride (GaN), the ternary alloys indium gallium nitride (InGaN), aluminum gallium nitride (AlGaN) and aluminum indium nitride (AlInN) as well as the quaternary alloy aluminum gallium indium nitride (AlInGaN) are attractive candidate materials for blue and UV lasers because of their relatively high bandgap (3.36 eV at room temperature for GaN). Accordingly, Group III-nitride based laser diodes have been demonstrated that emit light in the 370-420 nm range.

[0010] A number of commonly assigned patents and co-pending patent applications likewise discuss the design and manufacture of optoelectronic devices. For example, U.S. Pat. Nos. 6,459,100; 6,373,077; 6,201,262; 6,187,606; 5,912,477; and 5,416,342 describe various methods and structures for gallium-nitride based optoelectronic devices. U.S. Pat. No. 5,838,706 describes low-strain nitride laser diode structures. Published U.S. application Ser. Nos. 20020093020 and 20020022290 describe epitaxial structures for nitride-based optoelectronic devices. Various metal contact structures and bonding methods, including flip-chip bonding methods, are described in Published U.S. application Ser. No. 20020123164 as well as Published U.S. application Ser. No. 030045015 entitled “Flip Chip Bonding of Light Emitting Devices and Light Emitting Devices Suitable for Flip-Chip Bonding”; Published U.S. application Ser. No. 20030042507 entitled “Bonding of Light Emitting Diodes Having Shaped Substrates and Collets for Bonding of Light Emitting Diodes Having Shaped Substrates”, and Published U.S. application Ser. No. 20030015721 entitled “Light Emitting Diodes Including Modifications for Submount Bonding and Manufacturing Methods Therefor.” Dry etching methods are described in U.S. Pat. No. 6,475,889. Passivation methods for nitride optoelectronic devices are described in U.S. application Ser. No. 08/920,409 entitled “Robust Group III Light Emitting Diode for High Reliability in Standard Packaging Applications” and Published U.S. application Ser. No. 20030025121 entitled “Robust Group III Light Emitting Diode for High Reliability in Standard Packaging Applications.” Active layer structures suitable for use in nitride laser diodes are described in Published U.S. application Ser. No. 20030006418 entitled “Group III Nitride Based Light Emitting Diode Structures with a Quantum Well and Superlattice, Group III Nitride Based Quantum Well Structures and Group III Nitride Based Superlattice Structures” and Published U.S. application Ser. No. 20030020061 entitled “Ultraviolet Light Emitting Diode.” The contents of all of the foregoing patents, patent applications and published patent applications are incorporated entirely herein by reference as if fully set forth herein.

[0011] Not withstanding the structures and methods discussed above, further structures and/or methods providing improved beam quality, stability, voltage characteristics, guiding, and/or operating current characteristics may be desired.

SUMMARY

[0012] According to embodiments of the present invention, a light emitting device may include a silicon carbide substrate, and a semiconductor structure on the substrate. More particularly, the semiconductor structure may include a mesa having a mesa base adjacent the substrate, a mesa surface opposite the substrate, and mesa sidewalls between the mesa surface and the mesa base. In addition, the semiconductor structure may have a first conductivity type adjacent the silicon carbide substrate, the semiconductor structure may have a second conductivity type adjacent the mesa surface, and the semiconductor structure may have a junction between the first and second conductivity types. Moreover, the mesa may be configured to provide at least one of current confinement or optical confinement for a light emitting device in the semiconductor structure.

[0013] In one alternative, the junction may be between the mesa base and the mesa surface. In another alternative, the semiconductor structure may include a semiconductor base layer between the mesa base and the silicon carbide substrate and the junction may be between a surface of the base layer opposite the silicon carbide substrate and the silicon carbide substrate. Moreover, the semiconductor structure may include a Group III-V semiconductor material.

[0014] According to more embodiments of the present invention, an electronic device may include a substrate and a semiconductor mesa on the substrate. More particularly, the semiconductor mesa may have a mesa base adjacent the substrate, a mesa surface opposite the substrate, and mesa sidewalls between the mesa surface and the mesa base. Moreover, the semiconductor mesa may have a first conductivity type between the mesa base and a junction, the junction may be between the mesa base and the mesa surface, and the semiconductor mesa may have a second conductivity type between the junction and the mesa surface.

[0015] The junction may comprise a physical location where doping of the second conductivity type begins, the first conductivity type may be N-type, and the second conductivity type may be P-type. The semiconductor mesa may comprise a Group III-V semiconductor material such as a Group III-nitride semiconductor material.

[0016] In addition, the junction may be no more that approximately 5 microns from the mesa base, and more particularly, the junction may be no more than approximately 0.75 microns from the mesa base. Moreover, the junction may be at least approximately 0.05 microns from the mesa base, and more particularly, the junction may be at least approximately 0.1 microns from the mesa base. The semiconductor mesa may have a thickness in the range of approximately 0.1 microns to 5 microns.

[0017] A semiconductor base layer may be included between the substrate and the semiconductor mesa, and the semiconductor base layer may have the first conductivity type throughout. More particularly, the semiconductor base layer may have a thickness no greater than approximately 5 microns, and each of the semiconductor base layer and the semiconductor mesa may comprise a Group III-V semiconductor material. In addition, the substrate may comprise silicon carbide.

[0018] According to additional embodiments of the present invention, an electronic device may include a substrate, a semiconductor base layer on the substrate, and a semiconductor mesa on a surface of the base layer opposite the substrate. The semiconductor base layer may have a first conductivity type between the substrate and a junction, the junction may be between the substrate and a surface of the base layer opposite the substrate, and the semiconductor base layer may have a second. conductivity type between the junction and the surface of the base layer opposite the substrate. The semiconductor mesa may have a mesa surface opposite the semiconductor base layer and mesa sidewalls between the mesa surface and the base layer, and the semiconductor mesa may have the second conductivity type throughout.

[0019] The junction may be a physical location where doping of the second conductivity type begins, the first conductivity type may be N-type, and the second conductivity type may be P-type. Each of the semiconductor mesa and the semiconductor base layer may comprise a Group III-V semiconductor material such as a Group III-nitride semiconductor material.

[0020] The junction may be no more that approximately 0.4 microns from the surface of the base layer opposite the substrate, and more particularly, the junction may be no more than approximately 0.2 microns from the surface of the base layer opposite the substrate. In addition, the junction may be at least approximately 0.05 microns from the surface of the base layer opposite the substrate, and more particularly, the junction may be at least approximately 0.1 microns from the surface of the base layer opposite the substrate. Moreover, the semiconductor mesa may have a thickness in the range of approximately 0.1 microns to 5 microns, the semiconductor base layer may have a thickness no greater than approximately 5 microns. In addition, the substrate may comprise silicon carbide.

[0021] According to still additional embodiments of the present invention, methods of forming an electronic device may include forming a semiconductor mesa on a substrate. The semiconductor mesa may have a mesa base adjacent the substrate, a mesa surface opposite the substrate, and mesa sidewalls between the mesa surface and the mesa base. Moreover, the semiconductor mesa may have a first conductivity type between the mesa base and a junction, the junction may be between the mesa base and the mesa surface, and the semiconductor mesa may have a second conductivity type between the junction and the mesa surface.

[0022] The junction may comprise a physical location where doping of the second conductivity type begins, the first conductivity type may be N-type, and the second conductivity type may be P-type. The semiconductor mesa may comprise a Group III-V semiconductor material such as a Group III-nitride semiconductor material.

[0023] The junction may be no more that approximately 5 microns from the mesa base, and more particularly, the junction may be no more than approximately 0.75 microns from the mesa base. In addition, the junction may be at least approximately 0.05 microns from the mesa base, and more particularly, the junction may be at least approximately 0.1 microns from the mesa base. The semiconductor mesa may have a thickness in the range of approximately 0.1 microns to 5 microns.

[0024] In addition, a semiconductor base layer may be formed between the substrate and the semiconductor mesa, and the semiconductor base layer may have the first conductivity type throughout. More particularly, forming the semiconductor mesa and forming the semiconductor base layer may include forming a layer of a semiconductor material on the substrate, forming a mask on the layer of the semiconductor material, and etching portions of layer of the semiconductor material exposed by the mask wherein a depth of etching defines a thickness of the mesa. The layer of the semiconductor material may also include a junction at a junction depth and wherein the depth of etching of the layer of the semiconductor material is greater than the junction depth.

[0025] The semiconductor base layer may have a thickness no greater than approximately 5 microns, and each of the semiconductor base layer and the semiconductor mesa may comprise a Group III-V semiconductor material. The substrate may comprise silicon carbide.

[0026] According to yet additional embodiments of the present invention, methods of forming an electronic devices may include forming a semiconductor base layer on a substrate, and forming a semiconductor mesa of a surface of the base layer opposite the substrate. The semiconductor base layer may have a first conductivity type between the substrate and a junction, the junction may be between the substrate and a surface of the base layer opposite the substrate, and the semiconductor base layer may have a second conductivity type between the junction and the surface of the base layer opposite the substrate. The semiconductor mesa may have a mesa surface opposite the semiconductor base layer and mesa sidewalls between the mesa surface and the base layer, wherein the semiconductor mesa has the second conductivity type throughout.

[0027] The junction may include a physical location where doping of the second conductivity type begins, the first conductivity type may be N-type, and the second conductivity type may be P-type. Each of the semiconductor mesa and the semiconductor base layer may comprises a Group III-V semiconductor material such as a Group III-nitride semiconductor material. In addition, the junction is no more that approximately 0.4 microns from the surface of the base layer opposite the substrate, and more particularly, the junction may be no more than approximately 0.2 microns from the surface of the base layer opposite the substrate.

[0028] The junction may be at least approximately 0.05 microns from the surface of the base layer opposite the substrate, and more particularly, the junction may be at least approximately 0.1 microns from the surface of the base layer opposite the substrate. The semiconductor mesa may have a thickness in the range of approximately 0.1 microns to 5 microns. The semiconductor base layer may have a thickness no greater than approximately 5 microns, and the substrate may comprise silicon carbide.

[0029] In addition, forming the semiconductor mesa and forming the semiconductor base layer may include forming a layer of a semiconductor material on the substrate, forming a mask on the layer of the semiconductor material, and etching portions of layer of the semiconductor material exposed by the mask wherein a depth of etching defines a thickness of the mesa. More particularly, the semiconductor material may include a junction at a junction depth and wherein the depth of etching of the layer of the semiconductor material may be less than the junction depth.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a cross-sectional view illustrating semiconductor devices according to embodiments of the present invention.

[0031] FIG. 2 is a cross-sectional view illustrating semiconductor devices according to additional embodiments of the present invention.

[0032] FIG. 3 is a cross-sectional view illustrating semiconductor devices according to still additional embodiments of the present invention.

DETAILED DESCRIPTION

[0033] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. It will also be understood that when an element is referred to as being “coupled” or “connected” to another element, it can be directly coupled or connected to the other element, or intervening elements may also be present. Like numbers refer to like elements throughout. Furthermore, relative terms such as “vertical” and “horizontal” may be used herein to describe a relationship with respect to a substrate or base layer as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0034] As shown in the cross-section of FIG. 1, a semiconductor device according to embodiments of the present invention may include a substrate 12 and an epitaxial semiconductor structure 14 including a semiconductor base layer 19 and a semiconductor mesa 20 on a portion of the base layer 19. More particularly, the semiconductor mesa 20 may include a mesa surface 20A opposite the base layer 19, mesa sidewalls 20B between the mesa surface 20A and the base layer 19, and a mesa base 20C adjacent the base layer. While a dashed line is shown between the semiconductor mesa 20 and the semiconductor base layer 19 for purposes of illustration, it will be understood that adjacent portions of the semiconductor base layer 19 and the semiconductor mesa 20 may comprise a same semiconductor material with no physical barrier, junction, or discontinuity between the two.

[0035] The device may also include a passivation layer 24 on the semiconductor base layer 19 and on portions of the semiconductor mesa 20 with portions of the mesa surface 20A being free of the passivation layer 24. Moreover, a first ohmic contact layer 26 may be provided on portions of the mesa surface 20A free of the passivation layer, and a metal overlayer 28 may be provided on the passivation layer 24 and the ohmic contact layer 26. In addition, a second ohmic contact layer 27 may be provided on the substrate 12 opposite the semiconductor structure 14 to define an electrical current path through the mesa 20, the semiconductor base layer 19, and the substrate 12. In an alternative, a second ohmic contact layer may be provided on a same side of the substrate as the epitaxial semiconductor structure 14 so that current through the substrate 12 is not required.

[0036] In some embodiments, the substrate 12 may included substrate material such as N-type silicon carbide having a polytype such as 2H, 4H, 6H, 8H, 15R, and/or 3C; sapphire; gallium nitride; and/or aluminum nitride. Moreover, the substrate 12 may be conductive to provide a “vertical” device having a “vertical” current flow through the epitaxial semiconductor structure 14 and the substrate 12. In an alternative, the substrate 12 may be insulating or semi-insulating where both ohmic contacts are provided on a same side of the substrate to provide a “horizontal” device. A conductive substrate could also be used in a “horizontal” device. Moreover, the term substrate may be defined to include a non-patterned portion of the semiconductor material making up the semiconductor structure 14, and/or there may not be a material transition between the substrate 12 and the semiconductor structure 14.

[0037] Portions of the epitaxial semiconductor structure 14 may be patterned into a mesa stripe, for example, to provide optical and/or current confinement for a semiconductor laser device. As shown, only a portion of the epitaxial semiconductor structure 14 is included in the mesa 20. For example, the epitaxial semiconductor structure 14 may include N-type and P-type layers and portions of one or both of the N-type and P-type layers may be included in the mesa 20. According to particular embodiments, the epitaxial semiconductor structure 14 may include an N-type layer adjacent the substrate 12 and a P-type layer on the N-type layer opposite the substrate 12. The mesa may include portions of the P-type layer and none of the N-type layer. In alternatives, the mesa may include all of the P-type layer and portions (but not all) of the N-type layer; or all of the P-type layer and all of the N-type layer (such that sidewalls of the mesa 20 extend to the substrate 12).

[0038] The semiconductor structure 14 may also include a junction between the N-type and P-type layers. The junction, for example, may be a structural junction defined as a physical location in the semiconductor structure 14 where P-type doping begins. A structural junction and an actual electronic P-N junction may thus have different locations in the semiconductor structure 14 due to reactor effects, dopant incorporation rates, dopant activation rates, dopant diffusion, and/or other mechanisms.

[0039] The epitaxial semiconductor structure 14 may also include an active layer at the junction between the N-type layer and the P-type layer. The active layer may include a number of different structures and/or layers and/or combinations thereof. The active layer, for example, may include single or multiple quantum wells, double heterostructures, and/or superlattices. The active layer may also include light and/or current confinement layers that may encourage laser action in the device. Moreover, portions of the active layer may be included in the N-type layer and/or the P-type layer adjacent the junction therebetween. According to particular embodiments, the active layer may be included in the N-type layer adjacent the junction with the P-type layer.

[0040] By way of example, a uniformly thick layer of epitaxial semiconductor material may be formed on the substrate 12, and a layer of an ohmic contact material may be formed on the layer of the epitaxial semiconductor material. The semiconductor mesa 20 and the ohmic contact layer 26 may be formed, for example, by selectively etching the layer of the contact material and the layer of the epitaxial semiconductor material using a same etch mask, using different etch masks, and/or using a lift-off technique. Methods of forming mesas, contact layers, and passivation layers are discussed, for example, in U.S. application Ser. No. ______ (Attorney Docket No. 5308-280), in U.S. application Ser. No. ______ (Attorney Docket No. 5308-281), and in U.S. application Ser. No. ______ (Attorney Docket No. 5308-282), the disclosures of which are hereby incorporated herein by reference.

[0041] Exposed portions of the epitaxial semiconductor material can be removed using a dry etch such as a Reactive Ion Etch (RIE), an Electron Cyclotron Resonance (ECR) plasma etch, and/or an Inductively Coupled Plasma (ICP) etch. More particularly, the epitaxial semiconductor layer can be etched using a dry etch in an Argon (Ar) environment with a chlorine (Cl2) etchant. For example, argon can flow at a rate in the range of approximately 2 to 40 sccm and chlorine can flow at a rate in the range of approximately 5 to 50 sccm in an RIE reactor at a pressure in the range of approximately 5 to 50 mTorr and at an RF power in the range of approximately 200 to 1000 W. These etch parameters are provided by way of example, and other etch parameters may be used.

[0042] Moreover, thicknesses of the semiconductor base layer 19 and the semiconductor mesa 20 and a distance of a conductivity junction from the mesa base may be determined by an original thickness of the semiconductor layer from which the base layer and mesa are patterned, an original depth of the junction in the semiconductor layer, and a depth of an etch used to form the semiconductor mesa 20. According to embodiments of the present invention, the mesa etch depth (and resulting mesa thickness) may be in the range of approximately 0.1 to 5 microns, and according to additional embodiments may be no greater than approximately 2.5 microns. In addition, a width of the mesa surface 20A between mesa sidewalls 20B may be in the range of approximately 1 to 3 microns, and a distance Dsubstrate from the mesa base 20C to the substrate can be in the range of approximately 0 to 4.9 microns. The distance Dsubstrate is also a measure of the thickness of the semiconductor base layer 19. In addition, the mesa surface 20A may be a P-type semiconductor material.

[0043] The location of the junction in the semiconductor base layer 19 or the semiconductor mesa 20 can be determined by an original depth of the conductivity junction in the semiconductor layer from which the base layer and mesa are patterned. If the etch depth of the etch used to form the semiconductor mesa 20 is greater than a depth of the junction in the semiconductor layer, the junction can be in included in the resulting semiconductor mesa 20. In an alternative, if the etch depth of the etch used to form the semiconductor mesa 20 is less than a depth of the junction in the semiconductor layer, the junction can be included in the semiconductor base layer 19.

[0044] According to particular embodiments, the semiconductor mesa 20 may be formed such that the structural junction between N-type and P-type layers is included in the semiconductor base layer 19 spaced from the mesa base 20C by a distance of no more than approximately 0.4 microns, and more particularly, by a distance of no more than approximately 0.2 microns. By providing the structural junction in the semiconductor base layer 19 outside the semiconductor mesa 20, beam quality, stability, and/or voltage characteristics for a resulting semiconductor laser may be improved.

[0045] In an alternative, the semiconductor mesa 20 may be formed such that the structural junction between N-type and P-type layers is included in the semiconductor mesa 20 spaced from the mesa base 20C by a distance of no more than approximately 5 microns, and more particularly, by a distance of no more than approximately 0.75 microns. By providing the structural junction in the semiconductor mesa 20, a resulting semiconductor laser may provide stronger guiding and/or improved operating current characteristics.

[0046] A semiconductor device according to particular embodiments of the present invention is illustrated in FIG. 2. As shown in FIG. 2, a semiconductor device may include a substrate 112 and an epitaxial semiconductor structure 114 including a semiconductor base layer 119 and a semiconductor mesa 120 on a portion of the base layer 119. More particularly, the semiconductor mesa 120 may include a mesa surface 120A opposite the base layer 119, mesa sidewalls 120B between the mesa surface 120A and the base layer 119, and a mesa base 120C adjacent the base layer. While a dashed line is shown between the semiconductor mesa 120 and the semiconductor base layer 119 for purposes of illustration, it will be understood that adjacent portions of the semiconductor base layer 119 and the semiconductor mesa 120 may comprise a same semiconductor material with no physical barrier, junction, or discontinuity between the two.

[0047] The device may also include a passivation layer 124 on the semiconductor base layer 119 and on portions of the semiconductor mesa 120 with portions of the mesa surface 120A being free of the passivation layer 124. Moreover, a first ohmic contact layer 126 may be provided on portions of the mesa surface 120A free of the passivation layer, and a metal overlayer 128 may be provided on the passivation layer 124 and the ohmic contact layer 126. In addition, a second ohmic contact layer 127 may be provided on the substrate 112 opposite the semiconductor structure 114 to define an electrical current path through the mesa 120, the semiconductor base layer 119, and the substrate 112. In an alternative, a second ohmic contact layer may be provided on a same side of the substrate as the epitaxial semiconductor structure 114 so that current through the substrate 112 is not required.

[0048] In some embodiments, the substrate 112 may include a substrate material such as N-type silicon carbide having a polytype such as 2H, 4H, 6H, 8H, 15R, and/or 3C; sapphire; gallium nitride; and/or aluminum nitride. Moreover, the substrate 112 may be conductive to provide a “vertical” device having a “vertical” current flow through the epitaxial semiconductor structure 114 and the substrate 112. In an alternative, the substrate 112 may be insulating or semi-insulating where both ohmic contacts are provided on a same side of the substrate to provide a “horizontal” device. A conductive substrate could also be used in a “horizontal” device. Moreover, the term substrate may be defined to include a non-patterned portion of the semiconductor material making up the semiconductor structure 114, and/or there may not be a material transition between the substrate 112 and the semiconductor structure 114.

[0049] Portions of the epitaxial semiconductor structure 114 may be patterned into a mesa stripe, for example, to provide optical and/or current confinement for a semiconductor laser device. As shown, only a portion of the epitaxial semiconductor structure 114 is included in the mesa 120, and the remainder of the epitaxial semiconductor structure 114 is included in the semiconductor base layer 119. More particularly, the epitaxial semiconductor structure 114 may include an N-type layer 115, all of which is included in the semiconductor base layer 119 adjacent the substrate 112. The epitaxial semiconductor structure 114 may also include a P-type layer (including portions 117′ and 117″) with a junction 122 between the N-type and P-type layers. As discussed above, the junction 122 may be a structural junction defined as a location where P-type doping begins. A structural junction and an actual electronic P-N junction may thus have different locations in the semiconductor structure 114 due to reactor effects, dopant incorporation rates, dopant activation rates, dopant diffusion, and/or other mechanisms.

[0050] As shown in FIG. 2, a first portion 117′ of the P-type layer is included in the semiconductor base layer 119, and a second portion 117″ of the P-type layer is included in the semiconductor mesa 120. A thickness of the first portion 117′ of the P-type layer is the same as the distance (labeled D′junction) from the mesa base 120C to the junction 122 in the semiconductor base layer 119, and the thickness of the second portion 117″ of the P-type layer (labeled T′) is the same as the thickness of the semiconductor mesa 120. In addition, a distance D′substrate between the mesa base 120C and the substrate 112 is the same as a thickness of the semiconductor base layer 119. Accordingly, a thickness of the N-type layer 115 may be equal to a difference of D′substrate minus D′junction.

[0051] According to particular embodiments, the semiconductor mesa 120 may be formed such that the junction 122 between N-type and P-type layers is included in the semiconductor base layer 119 spaced from the mesa base 120C by a distance D′junction of no more than approximately 0.4 microns, and more particularly, by a distance of no more than approximately 0.2 microns. In addition, the junction 122 may be included in the semiconductor base layer 119 spaced from the mesa base 120C by a distance D′junction of at least approximately 0.05 microns, and more particularly, the junction 122 may be included in the semiconductor base layer 119 spaced from the mesa base 120C by a distance D′junction of at least approximately 0.1 microns. By providing the structural junction in the semiconductor base layer 119 outside the semiconductor mesa 120, beam quality, stability, and/or voltage characteristics for a resulting semiconductor laser may be improved.

[0052] The epitaxial semiconductor structure 114 may also include an active layer at the junction 122 between the N-type layer and the P-type layer. The active layer may include a number of different structures and/or layers and/or combinations thereof. The active layer, for example, may include single or multiple quantum wells, double heterostructures, and/or superlattices. The active layer may also include light and/or current confinement layers that may encourage laser action in the device. Moreover, portions of the active layer may he included in the N-type layer and/or the P-type layer adjacent the junction therebetween. According to particular embodiments, the active layer may be included in the N-type layer 115 adjacent the junction 122 with the P-type layer.

[0053] By way of example, a uniformly thick layer of epitaxial semiconductor material may be formed on the substrate 112, and a layer of an ohmic contact material may be formed on the layer of the epitaxial semiconductor material. The semiconductor mesa 120 and the ohmic contact layer 126 may be formed, for example, by selectively etching the layer of the contact material and the layer of the epitaxial semiconductor material using a same etch mask, using different etch masks, and/or using a lift-off technique. Methods of forming mesas, contact layers, and passivation layers are discussed, for example, in U.S. application Ser. No. ______ (Attorney Docket No. 5308-280), in U.S. application Ser. No. ______ (Attorney Docket No. 5308-281), and in U.S. application Ser. No. ______ (Attorney Docket No. 5308-282), the disclosures of which are hereby incorporated herein by reference.

[0054] Exposed portions of the epitaxial semiconductor material can be removed using a dry etch such as a Reactive Ion Etch (RIE), an Electron Cyclotron Resonance (ECR) plasma etch, and/or an Inductively Coupled Plasma (ICP) etch. More particularly, the epitaxial semiconductor layer can be etched using a dry etch in an Argon (Ar) environment with a chlorine (Cl2) etchant. For example, argon can flow at a rate in the range of approximately 2 to 40 sccm and chlorine can flow at a rate in the range of approximately 5 to 50 sccm in an RIE reactor at a pressure in the range of approximately 5 to 50 mTorr and at an RF power in the range of approximately 200 to 1000 W. These etch parameters are provided by way of example, and other etch parameters may be used.

[0055] Moreover, thicknesses of the semiconductor base layer 119 and the semiconductor mesa 120 and the distance D′junction of the junction 112 from the mesa base 120C may be determined by an original thickness of the semiconductor layer from which the base layer 119 and mesa 120 are patterned, an original depth of the conductivity junction 122 in the semiconductor layer, and a depth of an etch used to form the semiconductor mesa 120. According to embodiments of the present invention, the mesa etch depth (and resulting mesa thickness T′) may be in the range of approximately 0.1 to 5 microns, and according to additional embodiments may be no greater than approximately 2.5 microns. In addition, a width of the mesa surface 120A between mesa sidewalls 120B may be in the range of approximately 1 to 3 microns, and a distance Dsubstrate from the mesa base 120C to the substrate can be in the range of approximately 0 to 4.9 microns. The distance Dsubstrate is also a measure of the thickness of the semiconductor base layer 119. In addition, the mesa surface 120A may be a P-type semiconductor material.

[0056] The location of the junction 122 in the semiconductor base layer 119 can be determined by an original depth (T′+D′junction) of the junction in the semiconductor layer from which the base layer and mesa are patterned and an etch depth T′ used to form the mesa 120. In particular, the etch depth T′ of the etch used to form the semiconductor mesa 120 can be less than the depth of the junction in the semiconductor layer so that the junction 122 is included in the semiconductor base layer 119.

[0057] A semiconductor device according to additional embodiments of the present invention is illustrated in FIG. 3. As shown in FIG. 3, a semiconductor device may include a substrate 212 and an epitaxial semiconductor structure 214 including a semiconductor base layer 219 and a semiconductor mesa 220 on a portion of the base layer 219. More particularly, the semiconductor mesa 220 may include a mesa surface 220A opposite the base layer 219, mesa sidewalls 220B between the mesa surface 220A and the base layer 219, and a mesa base 220C adjacent the base layer. While a dashed line is shown between the semiconductor mesa 220 and the semiconductor base layer 219 for purposes of illustration, it will be understood that adjacent portions of the semiconductor base layer 219 and the semiconductor mesa 220 may comprise a same semiconductor material with no physical barrier, junction, or discontinuity between the two.

[0058] The device may also include a passivation layer 224 on the semiconductor base layer 219 and on portions of the semiconductor mesa 220 with portions of the mesa surface 220A being free of the passivation layer 224. Moreover, a first ohmic contact layer 226 may be provided on portions of the mesa surface 220A free of the passivation layer, and a metal overlayer 228 may be provided on the passivation layer 224 and the ohmic contact layer 226. In addition, a second ohmic contact layer 227 may be provided on the substrate 212 opposite the semiconductor structure 214 to define an electrical current path through the mesa 220, the semiconductor base layer 219, and the substrate 212. In an alternative, a second ohmic contact layer may be provide on a same side of the substrate as the epitaxial semiconductor structure 214 so that current through the substrate 212 is not required.

[0059] In some embodiments, the substrate 212 may include a substrate material such as N-type silicon carbide having a polytype such as 2H, 4H, 6H, 8H, 15R, and/or 3C; sapphire; gallium nitride; and/or aluminum nitride. Moreover, the substrate 212 may be conductive to provide a “vertical” device having a “vertical” current flow through the epitaxial semiconductor structure 214 and the substrate 212. In an alternative, the substrate 212 may be insulating or semi-insulating where both ohmic contacts are provided on a same side of the substrate to provide a “horizontal” device. A conductive substrate could also be used in a “horizontal” device. Moreover, the term substrate may be defined to include a non-patterned portion of the semiconductor material making up the semiconductor structure 214, and/or there may not be a material transition between the substrate 212 and the semiconductor structure 214.

[0060] Portions of the epitaxial semiconductor structure 214 may be patterned into a mesa stripe, for example, to provide optical and/or current confinement for a semiconductor laser device. As shown, only a portion of the epitaxial semiconductor structure 214 is included in the mesa 220, and the remainder of the epitaxial semiconductor structure 214 is included in the semiconductor base layer 219. More particularly, the epitaxial semiconductor structure 214 may include a P-type layer 217, all of which is included in the semiconductor mesa 220 adjacent the mesa surface 220A. The epitaxial semiconductor structure 214 may also include an N-type layer (including portions 215′ and 215″) with a junction 222 between the P-type layer and the N-type layer. As discussed above, the junction 222 may be a structural junction defined as a location where P-type doping begins. A structural junction and an actual electronic P-N junction may thus have different locations in the semiconductor structure 114 due to reactor effects, dopant incorporation rates, dopant activation rates, dopant diffusion, and/or other mechanisms.

[0061] As shown in FIG. 3, a first portion 215′ of the N-type layer is included in the semiconductor base layer 219, and a second portion 215″ of the N-type layer is included in the semiconductor mesa 220. A thickness of the first portion 215′ of the N-type layer is the same as the distance (labeled D″substrate) from the mesa base 220C to the substrate 212, and the thickness of the second portion 215″ of the N-type layer (labeled D″junction) is the same as the distance from the mesa base 220C to the junction between the N-type and P-type layers. In addition, the thickness of the semiconductor mesa is labeled T″. Accordingly, a thickness of the P-type layer 217 may be equal to a difference of the mesa thickness T″ minus D″junction.

[0062] According to particular embodiments, the semiconductor mesa 220 may be formed such that the junction 222 between N-type and P-type layers is included in the mesa 220 spaced apart from the mesa base 220C by a distance D″junction of no more than approximately 5 microns, and more particularly, by a distance of no more than approximately 0.75 microns. In addition, the junction 222 may be included in the semiconductor mesa 220 spaced from the mesa base 220C by a distance D″junction of at least approximately 0.05 microns, and more particularly, the junction 222 may be included in the semiconductor mesa 220 spaced from the mesa base 220C by a distance D″junction of at least approximately 0.1 microns. By providing the structural junction in the semiconductor mesa 220 outside the semiconductor mesa 220, a resulting semiconductor laser may provide stronger guiding and/or improved operating current characteristics.

[0063] The epitaxial semiconductor structure 214 may also include an active layer at the junction between the N-type layer and the P-type layer. The active layer may include a number of different structures and/or layers and/or combinations thereof. The active layer, for example, may include single or multiple quantum wells, double heterostructures, and/or superlattices. The active layer may also include light and/or current confinement layers that may encourage laser action in the device. Moreover, portions of the active layer may be included in the N-type layer and/or the P-type layer adjacent the junction therebetween. According to particular embodiments, the active layer may be included in the second portion 215″ of the N-type layer adjacent the junction 222 with the P-type layer 217.

[0064] By way of example, a uniformly thick layer of epitaxial semiconductor material may be formed on the substrate 212, and a layer of an ohmic contact material may be formed on the layer of the epitaxial semiconductor material. The semiconductor mesa 220 and the ohmic contact layer 226 may be formed, for example, by selectively etching the layer of the contact material and the layer of the epitaxial semiconductor material using a same etch mask, using different etch masks, and/or using a lift-off technique. Methods of forming mesas, contact layers, and passivation layers are discussed, for example, in U.S. application Ser. No. ______ (Attorney Docket No. 5308-280), in U.S. application Ser. No. ______ (Attorney Docket No. 5308-281), and in U.S. application Ser. No. ______ (Attorney Docket No. 5308-282), the disclosures of which are hereby incorporated herein by reference.

[0065] Exposed portions of the epitaxial semiconductor material can be removed using a dry etch such as a Reactive Ion Etch (RIE), an Electron Cyclotron Resonance (ECR) plasma etch, and/or an Inductively Coupled Plasma (ICP) etch. More particularly, the epitaxial semiconductor layer can be etched using a dry etch in an Argon (Ar) environment with a chlorine (Cl2) etchant. For example, argon can flow at a rate in the range of approximately 2 to 40 sccm and chlorine can flow at a rate in the range of approximately 5 to 50 sccm in an RIE reactor at a pressure in the range of approximately 5 to 50 mTorr and at an RF power in the range of approximately 200 to 1000 W. These etch parameters are provided by way of example, and other etch parameters may be used.

[0066] Moreover, thicknesses of the semiconductor base layer 219 and the semiconductor mesa 220 and a distance D″junction of a junction from the mesa base 220C may be determined by an original thickness of the semiconductor layer from which the base layer 219 and mesa 220 are patterned, an original depth of the junction in the semiconductor layer, and a depth of an etch used to form the semiconductor mesa 220. According to embodiments of the present invention, the mesa etch depth (and resulting mesa thickness T″) may be in the range of approximately 0.1 to 5 microns, and according to additional embodiments may be no greater than approximately 2.5 microns. In addition, a width of the mesa surface 220A between mesa sidewalls 220B may be in the range of approximately 1 to 3 microns, and a distance Dsubstrate from the mesa base 220C to the substrate can be in the range of approximately 0 to 4.9 microns. The distance Dsubstrate is also a measure of the thickness of the semiconductor base layer 219. In addition, the mesa surface 220A may be a P-type semiconductor material.

[0067] The location of the junction 222 in the semiconductor mesa 220 can be determined by an original depth (T″−D″junction) of the junction in the semiconductor layer from which the base layer 219 and mesa 220 are patterned and an etch depth used to form the mesa 220. In particular, the etch depth T″ of the etch used to form the semiconductor mesa 220 can be greater than a depth of the junction in the semiconductor layer so that the junction can be included in the semiconductor base layer 219.

[0068] The resulting semiconductor devices may provide edge emitting semiconductor lasers with light being emitted parallel to the substrate along a lengthwise direction of a semiconductor mesa stripe. Stated in other words, the light may be emitted along a direction perpendicular to the cross section of the Figures discussed above. While methods and devices have been discussed with reference to methods of forming light emitting devices such as laser diodes, methods according to embodiments of the present invention may be used to form other semiconductor devices such as conventional diodes, conventional light emitting diodes, or any other semiconductor device including a semiconductor mesa.

[0069] While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.