Nitride semiconductor laser, epitaxial substrate

• US 8,923,354 B2
• Filed: 10/04/2012
• Issued: 12/30/2014
• Est. Priority Date: 01/05/2012
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.), Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Original Assignee: Sony Corporation (Sony Group Corp.), Sumitomo Electric Industries Limited (Sumitomo Corporation)
• Inventors: Kyono, Takashi, Enya, Yohei, Sumitomo, Takamichi, Yoshizumi, Yusuke, Ueno, Masaki, Yanashima, Katsunori, Tasai, Kunihiko, Nakajima, Hiroshi
• Primary Examiner(s): Matthews, Colleen A
• Assistant Examiner(s): King, Joshua
• Application Number:
  US13/644,478
• Publication Number:
  US 20130177035A1
• Time in Patent Office: 817 Days
• Field of Search: 372/43.01, 372/44.01
• US Class Current: 372/44.01
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01L 21/02389 Nitrides
• CPC Class Codes: H01L 21/02433 Crystal orientation
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01S 2304/04 MOCVD or MOVPE
• CPC Class Codes: H01S 5/2031 characterized by special waveguide layers, e.g. asymmetric waveguide layers or defined bandgap discontinuities
• CPC Class Codes: H01S 5/22 having a ridge or stripe structure
• CPC Class Codes: H01S 5/30 Structure or shape of the active region; Materials used for the active region
• CPC Class Codes: H01S 5/3063 using Mg
• CPC Class Codes: H01S 5/3201 incorporating bulkstrain effects, e.g. strain compensation, strain related to polarisation
• CPC Class Codes: H01S 5/320275 semi-polar orientation
• CPC Class Codes: H01S 5/3213 asymmetric clading layers
• CPC Class Codes: H01S 5/34333 with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser

Abstract

A nitride semiconductor laser comprises a conductive support base having a primary surface of gallium nitride based semiconductor, an active layer on the primary surface, and a p-type cladding region on the primary surface. The primary surface is tilted to a reference plane perpendicular to a reference axis extending in the c-axis direction of the gallium nitride based semiconductor. The p-type cladding region comprises a first p-type group III nitride semiconductor layer of an AlGaN layer anisotropically-strained, and a second p-type group III nitride semiconductor layer of material different from the AlGaN layer. The first p-type group III nitride semiconductor layer is provided between the second p-type group III nitride semiconductor layer and the active layer. The AlGaN layer has the largest bandgap in the p-type cladding region. The second p-type group III nitride semiconductor layer has a resistivity lower than the first p-type group III nitride semiconductor layer.

Claims

1. A nitride semiconductor laser comprising:

a support base having conductivity, the support base including a primary surface, the primary surface comprising a gallium nitride based semiconductor;

an active layer provided on the primary surface; and

a p-type nitride semiconductor region provided on the primary surface,

the primary surface being tilted with respect to a reference plane, the reference plane being perpendicular to a reference axis, the reference axis extending in a direction of a c-axis of the gallium nitride based semiconductor,

the active layer being provided between the support base and the p-type nitride semiconductor region,

the p-type nitride semiconductor region including a p-type cladding region,

the p-type cladding region including a first p-type group III nitride semiconductor layer and a second p-type group III nitride semiconductor layer,

the first p-type group III nitride semiconductor layer being provided between the second p-type group III nitride semiconductor layer and the active layer,

the first p-type group III nitride semiconductor layer including an AlGaN layer,

the second p-type group III nitride semiconductor layer comprising material different from material of the AlGaN layer of the first p-type group III nitride semiconductor layer,

the AlGaN layer including anisotropic strain,

the AlGaN layer of the first p-type group III nitride semiconductor layer having a largest band gap energy in the p-type cladding region, and

the second p-type group III nitride semiconductor layer having a resistivity lower than a resistivity of a first p-type group III nitride semiconductor layer,

wherein a thickness of the p-type cladding region ranges from 300 nm to 1000 nm, and the first and second p-type group III nitride semiconductor layers have thicknesses d1 and d2, respectively, such that the thickness of the second p-type group III nitride semiconductor layer satisfies a relation;

0.2≦

d2/(d1+d2)≦

0.6,

the first p-type group III nitride semiconductor layer being in physical contact with the second p-type group III nitride semiconductor layer,

the material of the first p-type group III nitride semiconductor layer is AlGaN, and

the first p-type group III nitride semiconductor layer is made of AlGaN and does not include any other layer of material different from AlGaN.

2. The nitride semiconductor laser according to claim 1,

further comprising an n-type cladding region provided between the active layer and the primary surface of the support base,

the n-type cladding region comprising an InAlGaN layer;

and

the AlGaN layer of the first p-type group III nitride semiconductor layer having an Al composition lower than an Al composition of the InAlGaN layer of the n-type cladding region.

3. The nitride semiconductor laser according to claim 1,

wherein a band gap energy of the first p-type group III nitride semiconductor layer is larger than a band gap energy of the second p-type group III nitride semiconductor layer.

4. The nitride semiconductor laser according to claim 1,

wherein a band gap energy of the first p-type group III nitride semiconductor layer ranges from 3.47 electron volts to 3.63 electron volts.

5. The nitride semiconductor laser according to claim 1,

wherein the first and second p-type group III nitride semiconductor layers are doped with magnesium (Mg), and

the first p-type group III nitride semiconductor layer has a magnesium concentration lower than a magnesium concentration of the second p-type group III nitride semiconductor layer.

6. The nitride semiconductor laser according to claim 1,

wherein a magnesium concentration of the first p-type group III nitride semiconductor layer ranges from 8×

10¹⁷ cm<sup>−

3</sup> to 2×

10¹⁹ cm<sup>−

3</sup>.

7. The nitride semiconductor laser according to claim 1,

wherein an angle formed between the reference axis and the primary surface of the support base is in a range of one of 10 degrees to 80 degrees and 100 degrees to 170 degrees.

8. The nitride semiconductor laser according to claim 1,

wherein an angle formed between the reference axis and the primary surface of the support base is in a range of one of 63 degrees to 80 degrees and 100 degrees to 117 degrees.

9. The nitride semiconductor laser according to claim 1, further comprising an electrode in contact with the p-type nitride semiconductor region,

the p-type nitride semiconductor region comprising a p-type contact region, the p-type contact region being provided on the p-type cladding region, and the p-type contact region forming a junction with the electrode,

a thickness of the p-type contact region being smaller than 300 nm, and

a band gap energy of the p-type cladding region being not less than a band gap energy of the p-type contact region.

10. The nitride semiconductor laser according to claim 1, further comprising an electrode in contact with the p-type nitride semiconductor region,

the p-type nitride semiconductor region comprising a p-type contact region, the p-type contact region being provided on the p-type cladding region, and the p-type contact region forming a junction with the electrode, and

a p-type dopant concentration of the second p-type group III nitride semiconductor layer being lower than a p-type dopant concentration in the p-type contact region.

11. The nitride semiconductor laser according to claim 10, wherein a resistivity of the second p-type group III nitride semiconductor layer is smaller than a resistivity of the p-type contact region.

12. The nitride semiconductor laser according to claim 1, wherein the second p-type group III nitride semiconductor layer includes an InAlGaN layer, and the InAlGaN layer includes strain.

13. The nitride semiconductor laser according to claim 1, wherein the second p-type group III nitride semiconductor layer includes a GaN layer.

14. The nitride semiconductor laser according to claim 1, wherein the active layer is provided so as to emit light having a wavelength of 480 nm to 550 nm.

15. The nitride semiconductor laser according to claim 1, further comprising:

an n-side InGaN optical guiding layer provided between the active layer and the support base; and

a p-side InGaN optical guiding layer provided between the active layer and the p-type cladding region,

a thickness of the n-side InGaN optical guiding layer being larger than a thickness of the p-side InGaN optical guiding layer.

16. The nitride semiconductor laser according to claim 1, further comprising:

an n-side InGaN optical guiding layer provided between the active layer and the support base; and

a p-side InGaN optical guiding layer provided between the active layer and the p-type cladding region,

an indium composition of the n-side InGaN optical guiding layer being larger than an indium composition of the p-side InGaN optical guiding layer.

17. The nitride semiconductor laser according to claim 1, further comprising:

an n-side InGaN optical guiding layer provided between the active layer and the support base; and

a p-side InGaN optical guiding layer provided between the active layer and the p-type cladding region,

an indium composition of the n-side InGaN optical guiding layer being 0.04 or greater.

18. The nitride semiconductor laser according to claim 1, further comprising:

an n-side InGaN optical guiding layer provided between the active layer and the support base; and

a p-side InGaN optical guiding layer provided between the active layer and the p-type cladding region,

a product of a thickness of the n-side InGaN optical guiding layer and an indium composition of the n-side InGaN optical guiding layer being larger than a product of a thickness of the p-side InGaN optical guiding layer and an indium composition of the p-side InGaN optical guiding layer, and

the product of the thickness of the n-side InGaN optical guiding layer and the indium composition of the n-side InGaN optical guiding layer ranging from 2 to 10, the thickness of the n-side InGaN optical guiding layer being expressed in terms of nanometers, and the indium composition of the n-side InGaN optical guiding layer being expressed in terms of a molar ratio of the group III constituent elements thereof.

19. The nitride semiconductor laser according to claim 15, further comprising a nitride semiconductor layer provided between the n-side InGaN optical guiding layer and the primary surface of the support base,

the n-side InGaN optical guiding layer being provided between the nitride semiconductor layer and the active layer, and a density of misfit dislocations at an interface between the n-side InGaN optical guiding layer and the nitride semiconductor layer ranging from 5×

10³ cm<sup>−

1</sup> to 1×

10⁵ cm<sup>−

1</sup>.

20. An epitaxial substrate for a nitride semiconductor laser, comprising:

a substrate having a primary surface, the primary surface

comprising a gallium nitride based semiconductor;

an active layer provided on the primary surface; and

a p-type nitride semiconductor region provided on the primary

surface,

the primary surface being tilted with respect to a reference plane, the reference plane being perpendicular to a reference axis, and the reference axis extending in a direction of a c-axis of the gallium nitride based semiconductor,

the active layer being provided between the substrate and the p-type nitride semiconductor region,

the p-type nitride semiconductor region comprising a p-type cladding region,

the p-type cladding region including a first p-type group III nitride semiconductor layer and a second p-type group III nitride semiconductor layer,

the first p-type group III nitride semiconductor layer being provided between the second p-type group III nitride semiconductor layer and the active layer,

the first p-type group III nitride semiconductor layer comprising an AlGaN layer,

the second p-type group III nitride semiconductor layer being different from the AlGaN layer of the first p-type group III nitride semiconductor layer,

the AlGaN layer including anisotropic strain,

a band gap of the AlGaN layer of the first p-type group III nitride semiconductor layer being largest in the p-type cladding region, and

the second p-type group III nitride semiconductor layer having a resistivity lower than a resistivity of a first p-type group III nitride semiconductor layer,

wherein a thickness of the p-type cladding region ranges from 300 nm to 1000 nm, and the first and second p-type group III nitride semiconductor layers have thicknesses d1 and d2, respectively, such that the thickness of the second p-type group III nitride semiconductor layer satisfies a relation;

0.2≦

d2/(d1+d2)≦

0.6,

the first p-type group III nitride semiconductor layer being in physical contact with the second p-type group III nitride semiconductor layer,

the material of the first p-type group III nitride semiconductor layer is AlGaN, and

the first p-type group III nitride semiconductor layer is made of AlGaN and does not include any other layer of material different from AlGaN.

21. The epitaxial substrate according to claim 20, further comprising:

an n-type cladding region provided between the primary surface of the substrate and the active layer,

the n-type cladding region including an InAlGaN layer, and an Al composition of the AlGaN layer of the first p-type group III nitride semiconductor layer being lower than an Al composition of the InAlGaN layer of the n-type cladding region.

22. The epitaxial substrate according to claim 21, further comprising an InGaN optical guiding layer provided between the active layer and the substrate,

a density of misfit dislocations at an interface between the InGaN optical guiding layer and the n-type cladding region ranging from 5×

10³ cm<sup>−

1</sup> to 1×

10⁵ cm<sup>−

1</sup>.

23. The epitaxial substrate according to claim 20, wherein the p-type nitride semiconductor region comprises a p-type contact region provided on the p-type cladding region,

a thickness of the p-type contact region is smaller than 300 nm, and

a band gap energy of the p-type cladding region is not less than a band gap energy of the p-type contact region.

24. The epitaxial substrate according to claim 20,

wherein the p-type nitride semiconductor region includes a p-type contact region provided on the p-type cladding region, and

a p-type dopant concentration of the second p-type group III nitride semiconductor layer is lower than a p-type dopant concentration of the p-type contact region.