Semiconductor laser element, manufacturing method thereof, optical disk apparatus and optical transmission system

• US 7,492,801 B2
• Filed: 11/09/2004
• Issued: 02/17/2009
• Est. Priority Date: 11/11/2003
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Kawanishi, Hidenori, Kishimoto, Katsuhiko
• Primary Examiner(s): Harvey; Minsun
• Assistant Examiner(s): Stafford; Patrick
• Application Number:
  US10/983,761
• Publication Number:
  US 20050152419A1
• Time in Patent Office: 1,561 Days
• Field of Search: 372/43.01
• US Class Current: 372/43.01
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01S 2301/18 Semiconductor lasers with special structural design for influencing the near- or far-field
• CPC Class Codes: H01S 5/22 having a ridge or stripe structure
• CPC Class Codes: H01S 5/3211 characterised by special cladding layers, e.g. details on band-discontinuities
• CPC Class Codes: H01S 5/34353 based on (AI)GaAs

Abstract

A semiconductor laser element has a lower cladding layer of first conductivity type, an active layer, a first upper cladding layer of second conductivity type, and a second upper cladding layer of second conductivity type, which are stacked in this order on a semiconductor substrate of first conductivity type. The laser element further has a third upper cladding layer of second conductivity type and a contact layer of second conductivity type, which constitute a stripe-shaped ridge structure. A second-conductivity-type doping concentration of the second upper cladding layer is lower than those of the first and third upper cladding layers and is not higher than 1×10¹⁷ cm⁻³. A sum total of layer thicknesses of the first and second upper cladding layers is 0.3-1.5 μm, inclusive. An electrode layer forms an ohmic junction with the contact layer, and a Schottky junction with the second upper cladding layer.

Claims

1. A semiconductor laser element comprising:

a semiconductor substrate of first conductivity type;

a lower cladding layer of first conductivity type, an active layer, a first upper cladding layer of second conductivity type, and a second upper cladding layer of second conductivity type, which are stacked in this order on the semiconductor substrate;

a third upper cladding layer of second conductivity type and a contact layer of second conductivity type, which are formed directly or via a semiconductor layer of second conductivity type on the second upper cladding layer and constitute a stripe-shaped ridge structure; and

an electrode layer, wherein

a second-conductivity-type doping concentration of the second upper cladding layer is lower than second-conductivity-type doping concentrations of the first upper cladding layer and the third upper cladding layer and is not higher than 1×

10¹⁷ cm<sup>−

3;</sup>

a sum total of a layer thickness of the first upper cladding layer and a layer thickness of the second upper cladding layer is 0.3 m-1.5 μ

m, inclusive, and

the electrode layer forms an ohmic junction with the contact layer, and the electrode layer forms a Schottky junction with at least part of the second upper cladding layer located beside the ridge structure when the electrode layer is directly formed on the second upper cladding layer, and when the electrode layer is formed on the second upper cladding layer via the semiconductor layer of second conductivity type, the electrode layer forms a Schottky junction with at least part of the semiconductor layer of second conductivity type located beside the ridge structure.

2. The semiconductor laser element as claimed in claim 1, wherein

the semiconductor layer of second conductivity type is constructed of a material over which the third upper cladding layer and the contact layer are selectively etchable,

the semiconductor layer of second conductivity type has a second-conductivity-type doping concentration lower than second-conductivity-type doping concentrations of the first upper cladding layer and the third upper cladding layer, and

the electrode layer forms the Schottky junction with the semiconductor layer of second conductivity type.

3. The semiconductor laser element as claimed in claim 1, wherein

the ridge structure has a cross section of a forward mesa shape, and

the electrode layer continuously covers a top and side surfaces of the ridge structure and an upper surface of either the second upper cladding layer or the semiconductor layer of second conductivity type.

4. The semiconductor laser element as claimed in claim 3, wherein

a metal wire for obtaining electrical connection to an external circuit is bonded to only a portion of the electrode layer at which the electrode layer forms the Schottky junction with the second upper cladding layer or the semiconductor layer of second conductivity type.

5. The semiconductor laser element as claimed in claim 1, wherein

the semiconductor substrate of first conductivity type is made of n-type doped GaAs, and second-conductivity-type dopants for the first upper cladding layer, the second upper cladding layer, the third upper cladding layer, the contact layer and the semiconductor layer comprise carbon or magnesium.

6. The semiconductor laser element as claimed in claim 1, wherein

a crystalline material that constitutes the substrate comprises GaAs, and

crystalline materials that constitute the first upper cladding layer, the second upper cladding layer and the third upper cladding layer, respectively, comprise AlGaAs.

7. The semiconductor laser element as claimed in claim 1, wherein

crystalline materials that constitute the first upper cladding layer and the second upper cladding layer, respectively, comprise Al_xGa_1-xAs, and a mole fraction x of Al in Al_xGa_1-xAs is 0.4≦

x≦

0.55.

8. The semiconductor laser element as claimed in claim 1, wherein

the thickness of the second upper cladding layer is 0.1 μ

m-0.4 μ

m, inclusive.

9. The semiconductor laser element as claimed in claim 1, wherein

the second-conductivity-type doping concentration of the second upper cladding layer is 1×

10¹⁶ cm<sup>−

3</sup>-1×

10¹⁷ cm<sup>−

3</sup>, inclusive.

10. The semiconductor laser element as claimed in claim 1, wherein

the thickness of the first upper cladding layer is 0.2 μ

m-1.1 μ

m, inclusive.

11. The semiconductor laser element as claimed in claim 1, wherein

the second-conductivity-type doping concentration of the first upper cladding layer is not lower than 1×

10¹⁷ cm<sup>−

3</sup>.

12. The semiconductor laser element as claimed in claim 2, wherein

a crystalline material that constitutes the semiconductor layer of second conductivity type contains P.

13. The semiconductor laser element as claimed in claim 2, wherein

a crystalline material that constitutes the semiconductor layer of second conductivity type is In_1-xGa_xAs_1-yP_y, and its P mole fraction y is 0.4≦

y≦

0.7.

14. The semiconductor laser element as claimed in claim 2, wherein

a crystalline material that constitutes the semiconductor layer of second conductivity type is InGaAsP, which has a thickness of not smaller than 50 Å

and a second-conductivity-type doping concentration of 1×

10¹⁶ cm<sup>−

3</sup>-1×

10¹⁷ cm<sup>−

3</sup>, inclusive.

15. The semiconductor laser element as claimed in claim 1, wherein

the electrode layer has a Pt layer as a lowermost layer, and the Pt layer has a thickness of 30 Å

-400 Å

, inclusive.

16. The semiconductor laser element as claimed in claim 1, wherein

an insulator is provided in a stripe shape along each of opposite sides of the ridge structure in a position surrounded by a side surface of the ridge structure, an upper surface of either the second upper cladding layer or the semiconductor layer of second conductivity type, and the electrode layer.

17. The semiconductor laser element as claimed in claim 1, wherein

a stripe-shaped structure whose uppermost portion is higher than an uppermost portion of the ridge structure is provided on each of opposite sides of the ridge structure.

18. The semiconductor laser element as claimed in claim 17, wherein

the uppermost portion side of the stripe-shaped structure defines a bonding surface.

19. The semiconductor laser element as claimed in claim 17, wherein

the stripe-shaped structure has a third upper cladding layer, a contact layer, and a current cutoff layer whose second-conductivity-type doping concentration is not higher than 1×

10¹⁷ cm<sup>−

3</sup>, which layers are stacked in this order on the second upper cladding layer;

the electrode layer covers the stripe-shaped structure, and

the electrode layer forms a Schottky junction with the current cutoff layer of the stripe-shaped structure.

20. The semiconductor laser element as claimed in claim 17, wherein

the stripe-shaped structure comprises a conductor formed on the electrode layer.

21. The semiconductor laser element as claimed in claim 20, wherein

the conductor is gold or an alloy that contains gold.

22. The semiconductor laser element as claimed in claim 17, wherein

the stripe-shaped structure has a stack of semiconductor layers identical to that of the ridge structure, and an insulator formed on a periphery of the stack of semiconductor layers, and

the electrode layer is formed so as to cover the insulator.

23. The semiconductor laser element as claimed in claim 22, wherein

the insulator is silicon oxide or silicon nitride.

24. An optical disk apparatus having a semiconductor laser element as a light emitting device, said semiconductor laser element comprising:

a semiconductor substrate of first conductivity type;

a lower cladding layer of first conductivity type, an active layer, a first upper cladding layer of second conductivity type, and a second upper cladding layer of second conductivity type, which are stacked in this order on the semiconductor substrate;

a third upper cladding layer of second conductivity type and a contact layer of second conductivity type, which are formed directly or via a semiconductor layer of second conductivity type on the second upper cladding layer and constitute a stripe-shaped ridge structure; and

an electrode layer, wherein

a second-conductivity-type doping concentration of the second upper cladding layer is lower than second-conductivity-type doping concentrations of the first upper cladding layer and the third upper cladding layer and is not higher than 1×

10¹⁷ cm<sup>−

3</sup>;

a sum total of a layer thickness of the first upper cladding layer and a layer thickness of the second upper cladding layer is 0.3 μ

m-1.5 μ

m, inclusive, and

the electrode layer forms an ohmic junction with the contact layer, and the electrode layer forms a Schottky junction with at least part of the second upper cladding layer located beside the ridge structure when the electrode layer is directly formed on the second upper cladding layer, and when the electrode layer is formed on the second upper cladding layer via the semiconductor layer of second conductivity type, the electrode layer forms a Schottky junction with at least part of the semiconductor layer of second conductivity type located beside the ridge structure.

25. An optical transmission system having a semiconductor laser element as a light source, said semiconductor laser element comprising:

a semiconductor substrate of first conductivity type;

a lower cladding layer of first conductivity type, an active layer, a first upper cladding layer of second conductivity type, and a second upper cladding layer of second conductivity type, which are stacked in this order on the semiconductor substrate;

a third upper cladding layer of second conductivity type and a contact layer of second conductivity type, which are formed directly or via a semiconductor layer of second conductivity type on the second upper cladding layer and constitute a stripe-shaped ridge structure; and

an electrode layer, wherein

a second-conductivity-type doping concentration of the second upper cladding layer is lower than second-conductivity-type doping concentrations of the first upper cladding layer and the third upper cladding layer and is not higher than 1×

10¹⁷ cm<sup>−

3;</sup>

a sum total of a layer thickness of the first upper cladding layer and a layer thickness of the second upper cladding layer is 0.3 μ

m-1.5 μ

m, inclusive, and

the electrode layer forms an ohmic junction with the contact layer, and the electrode layer forms a Schottky junction with at least part of the second upper cladding layer located beside the ridge structure when the electrode layer is directly formed on the second upper cladding layer, and when the electrode layer is formed on the second upper cladding layer via the semiconductor layer of second conductivity type, the electrode layer forms a Schottky junction with at least part of the semiconductor layer of second conductivity type located beside the ridge structure.

26. A semiconductor laser element comprising:

a substrate of first conductivity type, an active layer formed on the substrate of first conductivity type and a stack of semiconductor layers of second conductivity type formed on the active layer, wherein

the stack of semiconductor layers of second conductivity type comprises at least a low-concentration semiconductor layer having a doping concentration of not higher than 1×

10¹⁷ cm<sup>−

3</sup> and a high-concentration semiconductor layer having a doping concentration of not lower than 1×

10¹⁸ cm<sup>−

3</sup>,

an electrode is formed on the stack of semiconductor layers of second conductivity type,

a low concentration-side compound layer is formed at an interface between the electrode and the low-concentration semiconductor layer, said low concentration-side compound layer being comprised of at least one of constituent elements of the electrode and at least one of constituent elements of the low-concentration semiconductor layer, and

a high concentration-side compound layer is formed at an interface between the electrode and the high-concentration semiconductor layer, said high concentration-side compound layer being comprised of at least one of the constituent elements of the electrode and at least one of constituent elements of the high-concentration semiconductor layer.

27. The semiconductor laser element as claimed in claim 26, wherein

the stack of semiconductor layers of second conductivity type comprises at least a semiconductor layer of second conductivity type that has a doping concentration of at least 1×

10¹⁷ cm<sup>−

3</sup> between the low-concentration semiconductor layer and the active layer.

28. The semiconductor laser element as claimed in claim 26, wherein

the high-concentration semiconductor layer is provided in an uppermost portion of a ridge structure, and

the low-concentration semiconductor layer is provided at least in a region other than the uppermost portion of the ridge structure.

29. The semiconductor laser element as claimed in claim 26, wherein

the high-concentration semiconductor layer is made of GaAs or InGaAs.

30. The semiconductor laser element as claimed in claim 26, wherein

the low-concentration semiconductor layer is made of AlGaAs.

31. The semiconductor laser element as claimed in claim 26, wherein

the low-concentration semiconductor layer contains at least In and P.

32. The semiconductor laser element as claimed in claim 31, wherein

the low-concentration semiconductor layer is made of any one of InGaP, InGaAsP, InGaAlP or InAlAsP.

33. The semiconductor laser element as claimed in claim 26, wherein

C or Mg or Be is used as a dopant for the stack of semiconductor layers of second conductivity type.

34. The semiconductor laser element as claimed in claim 26, wherein

the low concentration-side compound layer has a thickness of smaller than 0.2 μ

m.

35. The semiconductor laser element as claimed in claim 26, wherein

the electrode consists of a multilayer metal thin film, and a lowermost layer of the multilayer metal thin film is comprised of a platinum group element or a platinum group element compound.

36. The semiconductor laser element as claimed in claim 26, wherein

the low concentration-side compound layer contains a platinum group element.

37. The semiconductor laser element as claimed in claim 26, wherein

the electrode consists of a multilayer metal thin film, and a lowermost layer of the multilayer metal thin film is made of Ti.

38. The semiconductor laser element as claimed in claim 26, wherein

the low concentration-side compound layer contains at least Ti.

39. The semiconductor laser element as claimed in claim 28, wherein

a stripe-shaped structure whose uppermost portion is higher than the uppermost portion of the ridge structure is provided on each of opposite sides of the ridge structure.

40. The semiconductor laser element as claimed in claim 39, wherein

the uppermost portion side of the stripe-shaped structure defines a bonding surface.

41. The semiconductor laser element as claimed in claim 39, wherein

the low-concentration semiconductor layer is provided in the uppermost portion of the stripe-shaped structure.

42. The semiconductor laser element as claimed in claim 41, wherein

the low-concentration semiconductor layer provided in the uppermost portion of the stripe-shaped structure is made of InGaP or InGaAsP.

43. The semiconductor laser element as claimed in claim 39, wherein

the stripe-shaped structure is comprised of a conductor.

44. The semiconductor laser element as claimed in claim 43, wherein

the conductor is made of gold or an alloy that contains gold.

45. The semiconductor laser element as claimed in claim 39, wherein

an insulator is formed so as to cover the stripe-shaped structure, and

part of the electrode is formed on the insulator.

46. An optical disk apparatus having a semiconductor laser element as a light emitting device, said semiconductor laser element comprising:

a substrate of first conductivity type, an active layer formed on the substrate of first conductivity type and a stack of semiconductor layers of second conductivity type formed on the active layer, wherein

the stack of semiconductor layers of second conductivity type comprises at least a low-concentration semiconductor layer having a doping concentration of not higher than 1×

10¹⁷ cm<sup>−

3</sup> and a high-concentration semiconductor layer having a doping concentration of not lower than 1×

10 ¹⁸ cm <sup>−

3</sup>,

an electrode is formed on the stack of semiconductor layers of second conductivity type,

a low concentration-side compound layer is toned at an interface between the electrode and the low-concentration semiconductor layer, said low concentration-side compound layer being comprised of at least one of constituent elements of the electrode and at least one of constituent elements of the low-concentration semiconductor layer, and

a high concentration-side compound layer is formed at an interface between the electrode and the high-concentration semiconductor layer, said high concentration-side compound layer being comprised of at least one of the constituent elements of the electrode and at least one of constituent elements of the high-concentration semiconductor layer.

47. An optical transmission system having a semiconductor laser element as a light source, said semiconductor laser element comprising:

a substrate of first conductivity type, an active layer formed on the substrate of first conductivity type and a stack of semiconductor layers of second conductivity type formed on the active layer, wherein

the stack of semiconductor layers of second conductivity type comprises at least a low-concentration semiconductor layer having a doping concentration of not higher than 1×

10¹⁷ cm<sup>−

3</sup> and a high-concentration semiconductor layer having a doping concentration of not lower than 1×

10¹⁸ cm<sup>−

3</sup>,

an electrode is formed on the stack of semiconductor layers of second conductivity type,

a low concentration-side compound layer is formed at an interface between the electrode and the low-concentration semiconductor layer, said low concentration-side compound layer being comprised of at least one of constituent elements of the electrode and at least one of constituent elements of the low-concentration semiconductor layer, and

a high concentration-side compound layer is formed at an interface between the electrode and the high-concentration semiconductor layer, said high concentration-side compound layer being comprised of at least one of the constituent elements of the electrode and at least one of constituent elements of the high-concentration semiconductor layer.