Surface emission type semiconductor laser, method and apparatus for producing the same

• US 5,621,750 A
• Filed: 07/17/1995
• Issued: 04/15/1997
• Est. Priority Date: 01/20/1994
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Iwano, Hideaki, Asaka, Tatsuya, Kondo, Takayuki, Mori, Katsumi
• Primary Examiner(s): Davie, James W.
• Application Number:
  US08/491,955
• Time in Patent Office: 638 Days
• Field of Search: 372/96, 372/92, 372/45, 372/46, 437/129
• US Class Current: 372/96
• CPC Class Codes: H01S 2301/18 Semiconductor lasers with special structural design for influencing the near- or far-field
• CPC Class Codes: H01S 2304/04 MOCVD or MOVPE
• CPC Class Codes: H01S 5/0042 On wafer testing, e.g. lasers are tested before separating wafer into chips
• CPC Class Codes: H01S 5/0612 controlled by temperature
• CPC Class Codes: H01S 5/1221 Detuning between Bragg wavelength and gain maximum
• CPC Class Codes: H01S 5/18341 Intra-cavity contacts
• CPC Class Codes: H01S 5/18361 Structure of the reflectors, e.g. hybrid mirrors
• CPC Class Codes: H01S 5/18369 based on dielectric materials
• CPC Class Codes: H01S 5/2211 based on II-VI materials
• CPC Class Codes: H01S 5/2213 based on polyimide or resin
• CPC Class Codes: H01S 5/2214 based on oxides or nitrides
• CPC Class Codes: H01S 5/4068 with lateral coupling by axially offset or by merging waveguides, e.g. Y-couplers
• CPC Class Codes: H01S 5/423 having a vertical cavity

Abstract

A surface emission type semiconductor laser has insulation layers (107, 108) embedding separation grooves for partially separating the waveguide path in an optical resonator formed by a pair of reflecting mirrors, namely a distributed reflection type multilayer film mirror (104) and a dielectric multilayer film mirror (111), and a quantum well active layer (105).

A surface emission type semiconductor laser is designed such that the lasing wavelength λ_G of an edge emission type semiconductor laser having the same semiconductor layers as those of the optical resonator is set to be shorter than a desired lasing wavelength λ_EM of the surface emission type semiconductor laser by a given differential wavelength (gain offset) Δλ_EM.

Claims

1. A surface emission type semiconductor laser comprising:

a substrate formed of a compound semiconductor of a first conductance type;

a lower electrode formed on the bottom of said substrate;

a distributed reflection multilayer film mirror of the first conductance type formed on the top of said substrate;

a first clad layer of the first conductance type formed on said distributed reflection multilayer film mirror;

a quantum well active layer formed on said first clad layer;

a second clad layer of a second conductance type formed on said quantum well active layer and having one or more column-like portions;

a contact layer of the second conductance type formed on the column-like portion or portions in the second clad layer;

a buried insulation layer embedded around said column-like portion or portions of said second clad layer and said contact layer, including at least a first insulation layer which covers the surface of said second clad layer and said contact layer and which is formed of a silicon compound;

an upper electrode forming a bridge between said contact and buried insulation layers and having an opening facing part of said contact layer; and

a dielectric multilayer film mirror formed at least on said contact layer to cover the opening of said upper electrode.

2. A surface emission type semiconductor laser as defined in claim 1 wherein in addition to said first insulation layer, said buried insulation layer also includes a second insulation layer formed on said first insulation layer for flattening an area surrounding the column-like portion or portions of said second clad layer and said contact layer.

3. A surface emission type semiconductor laser as defined in claim 1 wherein said first insulation layer has its film thickness ranging between 500 Angstroms and 2000 Angstroms.

4. A surface emission type semiconductor laser as defined in claim 1 wherein said first insulation layer is formed of at least one material selected from a group consisting of silicon oxides, silicon nitrides and silicon carbides.

5. A surface emission type semiconductor laser as defined in claim 2 wherein said second insulation layer is formed of at least one material selected from a group consisting of silicon compounds formed at temperatures lower than that of the silicon compound of said first insulation layer, heat-resistant resins and polycrystalline II-VI group compound semiconductors.

6. A surface emission type semiconductor laser as defined in claim 1 wherein the film thickness of said second clad layer at the areas other than said column-like portion or portions is within a predetermined range.

7. A surface emission type semiconductor laser as defined in claim 6 wherein said film thickness is within a range between 0 and 0.58 μ

m.

8. A surface emission type semiconductor laser as defined in claim 7 wherein said film thickness is within a range between 0 and 0.35 μ

m.

9. A surface emission type semiconductor laser as defined in claim 1 wherein said quantum well active layer includes well layers formed of a III-V group compound semiconductor and barrier layers formed of a III-V group compound semiconductor and wherein the film thickness of each of said well layers is between 40 Angstroms and 120 Angstroms, the film thickness of each of said barrier layers being between 40 Angstroms and 100 Angstroms, and the total number of said well layers being between 3 and 40.

10. A surface emission type semiconductor laser as defined in claim 1 wherein said distributed reflection type multilayer film mirror has a reflectivity equal to or higher than 99.2% within range of a wavelength at least 40 nm which includes a lasing wavelength λ

_EM.

11. A surface emission type semiconductor laser as defined in claim 1 wherein said distributed reflection type multilayer film mirror comprising alternately stacked first and second type layers of first and second III-V group compound semiconductors, respectively, wherein said second compound semiconductor has an energy bandgap larger than that of said first compound semiconductor, and a refractive index different from that of said first compound semiconductor.

12. A surface emission type semiconductor laser as defined in claim 11 wherein the carrier concentration of the interface region between said first type layer and said second type layer is higher than that in the remaining regions of these layers.

13. A surface emission type semiconductor laser as defined in claim 11 wherein the maximum value of the carrier concentration of said interface region is between a minimum of 1.1 times and a maximum of 100 times the value of said remaining regions.

14. A surface emission type semiconductor laser as defined in claim 11 wherein the maximum value of the carrier concentration of said interface region is 5×

10²⁰ cm^-3 or less.

15. A surface emission type semiconductor laser as defined in claim 11 wherein the thickness of said interface region is within 1/3 of the total thickness of the two layers forming the interface.

16. A surface emission type semiconductor laser as defined in claim 11 wherein the dopants used to dope said interface region are selected from S, Se, Te and Si for an n-type region.

17. A surface emission type semiconductor laser as defined in claim 1 wherein said dielectric multilayer film mirror has a reflectivity between 98.5% and 99.5%.

18. A surface emission type semiconductor laser as defined in claim 17 wherein said dielectric multilayer film mirror is formed of a dielectric material having an absorption coefficient which is equal to or lower than 100 cm^-1 for the lasing wavelength.

19. A surface emission type semiconductor laser as defined in claim 18 wherein said dielectric multilayer film mirror is formed by alternately deposited layers of at least one material selected from a group consisting of SiO_x, MgF_x, CaF_x, BaF_x and AlF_x on the one hand.

20. A surface emission type semiconductor laser as defined in claim 1 wherein when the diameter of the column-like portion or portions in said second clad layer is Da and the diameter of the opening in said upper electrode is Dw, Da is between 6 μ

m and 12 μ

m and Dw is between 4 μ

m and 8 μ

m.

21. A surface emission type semiconductor laser as defined in claim 1 wherein said first and second clad layers include semiconductor layers of Al_x Ga_1-x As where x is equal to or larger than 0.65.

22. A surface emission type semiconductor laser as defined in claim 1 wherein the column-like portion or portions of said second clad layer has a film thickness between 0.8 μ

m and 3.5 μ

m.

23. A surface emission type semiconductor laser as defined in claim 1 wherein each column-like portion in said second clad layer has a rectangular cross-section parallel to the plane of said semiconductor substrate and having longer and shorter sides and wherein the plane of polarization in an emitted laser beam is parallel to said shorter sides.

24. A surface emission type semiconductor laser as defined in claim 23 wherein when said longer and shorter sides are respectively A and B, B<

A<

2B.

25. A surface emission type semiconductor laser as defined in claim 23 wherein said second clad layer includes a plurality of column-like portions each having a rectangular cross-section, the shorter sides of the rectangular column-like portions being parallel to one another, whereby laser beams aligned in phase and polarization plane with one another can be emitted from the column-like portions through said opening.

26. A surface emission type semiconductor laser as defined in claim 25 wherein said buried insulation layer is formed of transparent material, whereby laser beams aligned in phase and polarization plane with one another and each providing a single emission spot can be emitted from said column-like portions and said buried insulation layer between said column-like portions through said opening.

27. A surface emission type semiconductor laser as defined in claim 25 wherein said column-like portions each having a rectangular cross-section are disposed in linear symmetry on a two-dimensional plane parallel to said semiconductor substrate and wherein the opening formed in said upper electrode is of a circular or regularly polygonal configuration, whereby a laser beam of substantially circular cross-section can be emitted from said surface emission type semiconductor laser.

28. A surface emission type-semiconductor laser as defined in claim 25 wherein a plurality of optical resonators each including a plurality of said column-like portions are formed on said semiconductor substrate such that each of said optical resonators has an independent upper electrode, whereby a laser beam having a substantially circular emission spot emitted from each of said optical resonators can independently be turned on and off and modulated.

29. A surface emission type semiconductor laser as defined in claim 28 wherein said optical resonators includes column-like portions of rectangular cross-section with all the shorter sides thereof being parallel to one another, whereby the planes of polarization in the laser beams emitted from the respective optical resonators can be aligned with one direction.

30. A surface emission type semiconductor laser as defined in claim 28 wherein at least one of said optical resonators includes column-like portions having their shorter sides not parallel to those of the other optical resonator or resonators, whereby the plane of polarization in the laser beam emitted said at least one optical resonator can be different from the planes of polarization of the laser beams from the other optical resonators.

31. A surface emission type semiconductor laser as defined in claim 25 wherein said column-like portions are disposed equidistantly on a two-dimensional plane parallel to the plane of said semiconductor substrate in transverse and/or longitudinal lines, whereby said surface emission type semiconductor laser can emit a line laser beam.

32. A surface emission type semiconductor laser as defined in claim 1 wherein said opening is of a rectangular configuration having longer and shorter sides.

33. A surface emission type semiconductor laser as defined in claim 32 wherein when the longer sides are a and the shorter sides are b, b<

a<

2b.

34. A surface emission type semiconductor laser comprising:

a substrate formed of a compound semiconductor of a first conductance type;

a lower electrode formed on the bottom of said substrate;

a distributed reflection multilayer film mirror of the first conductance type formed on the top of said substrate;

a first clad layer of the first conductance type formed on said distributed reflection multilayer film mirror;

a quantum well active layer formed on said first clad layer;

a second clad layer of a second conductance type formed on said quantum well active layer and having one or more column-like portions;

a contact layer of the second conductance type formed on the column-like portion or portions in the second clad layer;

a buried insulation layer embedded around said column-like portion or portions of said second clad layer and said contact layer;

an upper electrode formed to bridge between said contact and buried insulation layers and having an opening facing a part of said contact layer; and

a dielectric multilayer film mirror formed at least on said contact layer to cover the opening of said upper electrode,

wherein the peak wavelength λ

_G of the gain spectrum of said quantum well active layer is set to be smaller than a desired lasing wavelength λ

_EM by a given differential wavelength (gain offset) Δ

λ

_BS.

35. A surface emission type semiconductor laser as defined in claim 34 wherein said gain offset Δ

λ

_BS ranges between 5 nm and 20 nm.

36. A surface emission type semiconductor laser as defined in claim 34 wherein said buried insulation layer includes at least a first insulation layer of a silicon compound which covers the surface of said second clad layer and said contact layer.

37. A method of producing a surface emission type semiconductor laser, comprising the steps of:

(a) forming semiconductor layers including at least a distributed reflection type multilayer film mirror of a first conductance type, a first clad layer of the first conductance type, a quantum well active layer, a second clad layer of a second conductance type and a contact layer of the second conductance type on a substrate formed of a first conductance type compound semiconductor through epitaxial growth;

(b) etching said contact and second clad layers to form one or more column-like portions;

(c) forming a buried insulation layer including at least a first insulation layer of silicon compound covering the surface of said second clad layer and said contact layer around said column-like portion or portions;

(d) forming an upper electrode having an opening facing a part of said contact layer and bridging between said contact layer and said buried insulation layer; and

(e) forming a dielectric multilayer film mirror at least on said contact layer to cover the opening of said upper electrode.

38. A method of producing a surface emission type semiconductor laser as defined in claim 37 wherein after said first insulation layer has been formed, said buried insulation layer is formed with a second insulation layer on said first insulation layer for flattening an area surrounding the column-like portion or portions of said second clad layer and said contact layer.

39. A method of producing a surface emission type semiconductor laser as defined in claim 37 wherein said distributed reflection type multilayer film mirror is formed by alternately depositing semiconductor layers of lower and higher refractive indexes, said deposition of semiconductor layers being switched from one semiconductor layer deposition to the other semiconductor layer deposition at minimum and maximum point in a reflectivity profile which is determined during formation of said layers by irradiating light having a given wavelength onto the substrate, sensing its reflective spectrum and measuring the reflectivity profile on the semiconductor layer being formed on the substrate.

40. A method of producing a surface emission type semiconductor laser as defined in claim 37 wherein said step (b) comprises a step of irradiating light having its wavelength within a given range onto the substrate having said semiconductor layers, sensing its reflective spectrum and measuring a dip appearing in the reflective spectrum due to a standing wave of the optical resonator, during the etching step, whereby the depth of etching can be controlled.

41. A method of producing a surface emission type semiconductor laser as defined in claim 40 wherein the depth of etching is controlled such that the film thickness of said second clad layer at an area other than said column-like portion or portions is within a given range.

42. A method of producing a surface emission type semiconductor laser as defined in claim 41 wherein said film thickness is set to be within a range between 0 and 0.58 μ

m.

43. A method of producing a surface emission type semiconductor laser as defined in any one of claim 37 wherein after the step (a), a protective layer of SiO_x is formed on the surface of said semiconductor layers.

44. A method of producing a surface emission type semiconductor laser as defined in claim 43 wherein during the etching step, the depth of etching in said protective layer is controlled by irradiating light having a given wavelength onto the substrate on which said protective layer is formed, sensing its reflective spectrum and measuring the reflectivity profile.

45. A method of producing a surface emission type semiconductor laser as defined in claim 37 wherein the length of a resonator constituted by said semiconductor layers formed in the step (a) is controlled by etching before the step (d) and wherein the depth of etching is controlled, during the etching step, by irradiating light having its wavelength within a given range onto the substrate on which said semiconductor layers are formed, sensing its reflective spectrum and measuring a dip appearing on the reflective spectrum due to a standing wave of the optical resonator.

46. A method of producing a surface emission type semiconductor laser as defined in claim 37 wherein the step (a) comprises a step of forming said semiconductor layers through the metal-organic vapor phase deposition method.

47. A method of producing a surface emission type semiconductor laser as defined in claim 37 wherein the temperature of said substrate is maintained at a level within a range between 0°

C. and 40°

C. during the step (b).

49. A method of producing a surface emission type semiconductor laser as defined in claim 38 wherein said gain offset Δ

λ

_BS is set to be between 5 nm and 20 nm.

48. A method of producing a surface emission type semiconductor laser, comprising the steps of:

(a) forming semiconductor layers including at least a distributed reflection type multilayer film mirror of a first conductance type, a first clad layer of the first conductance type, a quantum well active layer, a second clad layer of a second conductance type and a contact layer of the second conductance type on a substrate formed of a first conductance type compound semiconductor through epitaxial growth;

(b) etching said contact and second clad layers to form one or more column-like portions;

(c'"'"') forming a buried insulation layer around said column-like portion or portions;

(d) forming an upper electrode having an opening facing a part of said contact layer and bridging between the contact layer and the buried insulation layer; and

(e) forming a dielectric multilayer film mirror at least on said contact layer to cover the opening of said upper electrode,

said semiconductor layers being controlled such that the peak wavelength λ

_G of the gain spectrum of said quantum well active layer is smaller than a desired lasing wavelength λ

_EM by a predetermined differential wavelength (gain offset) Δ

λ

_BS.

50. A method of producing a surface emission type semiconductor laser as defined in claim 48 wherein said step (c'"'"') includes a step of forming a first insulation layer of a silicon compound covering at least the surface of said second clad layer and said contact layer.