Method and device concerning III-nitride edge emitting laser diode of high confinement factor with lattice matched cladding layer

• US 10,554,017 B2
• Filed: 05/19/2016
• Issued: 02/04/2020
• Est. Priority Date: 05/19/2015
• Status: Active Grant

• Current Assignee: Yale University
• Original Assignee: Yale University
• Inventors: Han, Jung, Li, Yufeng, Yuan, Ge
• Primary Examiner(s): Niu, Xinning (Tom)
• Assistant Examiner(s): Hagan, Sean P
• Application Number:
  US15/574,739
• Publication Number:
  US 20180152003A1
• Time in Patent Office: 1,356 Days
• CPC Class Codes: H01L 21/306 Chemical or electrical treatment, e.g. electrolytic etching to form insulating layers H01L21/31
• CPC Class Codes: H01S 2304/04 MOCVD or MOVPE
• CPC Class Codes: H01S 5/0422 with n- and p-contacts on the same side of the active layer
• CPC Class Codes: H01S 5/2009 by using electron barrier layers
• CPC Class Codes: H01S 5/2081 using special etching techniques
• CPC Class Codes: H01S 5/305 characterised by the doping materials used in the laser structure
• CPC Class Codes: H01S 5/3211 characterised by special cladding layers, e.g. details on band-discontinuities
• CPC Class Codes: H01S 5/3213 asymmetric clading layers
• CPC Class Codes: H01S 5/3214 comprising materials from other groups of the periodic system than the materials of the active layer, e.g. ZnSe claddings and GaAs active layer
• CPC Class Codes: H01S 5/3219 explicitly Al-free cladding 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

Edge-emitting laser diodes having high confinement factors and lattice-matched, porous cladding layers are described. The laser diodes may be formed from layers of III-nitride material. A cladding layer may be electrochemically etched to form a porous cladding layer having a high refractive index contrast with an active junction of the device. A transparent conductive oxide layer may be deposited to form a top-side cladding layer with high refractive index contrast and low resistivity.

Claims

1. A semiconductor laser diode comprising an active region formed on a substrate and arranged for edge emission of a laser beam and a porous cladding layer formed between the substrate and the active region, wherein the porous cladding provides a refractive index difference from the active region such that the laser diode has a one-dimensional confinement factor Γ

_1D between 4% and 10%, and wherein the confinement factor represents a ratio of an integrated transverse electric field squared of the laser beam confined within the active region to a total amount of transverse electric field squared for the laser beam.

2. The semiconductor laser diode of claim 1, wherein a difference in a first refractive index value for the active region and a second refractive index value for the porous cladding layer is greater than 0.2.

3. The semiconductor laser diode of claim 1, wherein the porous cladding layer comprises n-doped GaN.

4. The semiconductor laser diode of claim 3, wherein a doping density of the porous cladding layer is between 1×

10¹⁸ cm<sup>−

3</sup> and 1×

10¹⁹ cm<sup>−

3</sup>.

5. The semiconductor laser diode of claim 4, further comprising an n-type GaN layer having a doping level between 1×

10¹⁸ cm<sup>−

3</sup> and 5×

10¹⁸ cm<sup>−

3</sup> located between the porous cladding layer and the substrate.

6. The semiconductor laser diode of claim 1, wherein a porosity of the porous cladding layer is between 30% and 60%.

7. The semiconductor laser diode of claim 6, wherein an average pore diameter for the porous cladding layer is between 10 nm and 100 nm.

8. The semiconductor laser diode of claim 1, wherein a thickness of the porous cladding layer is between 200 nm and 500 nm.

9. The semiconductor laser diode of claim 1, wherein the active region comprises multiple-quantum wells.

10. The semiconductor laser diode of claim 1, further comprising a conductive oxide cladding layer formed on a side of the active region opposite the porous cladding layer.

11. The semiconductor laser diode of claim 10, having a one-dimensional confinement factor Γ

_1D between 4% and 10%.

12. The semiconductor laser diode of claim 10, wherein the conductive oxide cladding layer comprises indium tin oxide.

13. The semiconductor laser diode of claim 1, incorporated as an optical source for a light.

24. The semiconductor laser diode of claim 1, wherein the n+-doped GaN layer is the only layer having a doping concentration greater than 5×

10¹⁸ cm<sup>−

3</sup> between the active region and the substrate.

14. A method for making a semiconductor laser diode, the method comprising:

forming an n+-doped GaN layer on a substrate;

forming an active junction for and edge-emitting semiconductor laser diode adjacent to the n+-doped GaN layer;

etching trenches through the active junction to expose a surface of the n+-doped GaN layer; and

subsequently wet etching the n+-doped GaN layer to convert the n+-doped GaN layer to a porous cladding layer that provides a refractive index difference from the active junction such that the laser diode has a one-dimensional confinement factor Γ

_1D between 4% and 10%, wherein the confinement factor represents a ratio of an integrated transverse electric field squared of the laser beam confined within the active junction to a total amount of transverse electric field squared for the laser beam.

15. The method of claim 14, further comprising forming a conductive oxide cladding layer adjacent to the active junction.

16. The method of claim 14, further comprising forming an n-type current spreading layer adjacent to the n+-doped GaN layer, wherein a doping concentration of the n-type current spreading layer is between 1×

10¹⁸ cm<sup>−

3</sup> and 5×

10¹⁸ cm<sup>−

3</sup>.

17. The method of claim 14, wherein forming an active junction comprises depositing n-type GaN, multiple quantum wells, and p-type GaN by epitaxy.

18. The method of claim 14, wherein the wet etching is performed after forming the active junction.

19. The method of claim 14, wherein the wet etching comprises electrochemical etching that laterally porosifies the n+-doped GaN layer and does not require photo-assisted etching.

20. The method of claim 19, wherein the wet etching uses nitric acid as an electrolyte to porosify the n+-doped GaN layer.

21. The method of claim 19, wherein the wet etching uses hydrofluoric acid as an electrolyte to porosify the n+-doped GaN layer.

22. The method of claim 14, wherein the n+-doped GaN layer has a doping concentration between 5×

10¹⁸ cm<sup>−

3</sup> and 2×

10²⁰ cm<sup>−

3</sup>.

23. The method of claim 22, wherein the n+-doped GaN layer is the only layer having a doping concentration greater than 5×

10¹⁸ cm<sup>−

3</sup> between the active junction and the substrate.