SURFACE EMITTING QUANTUM CASCADE LASER

• US 20190074663A1
• Filed: 09/04/2018
• Published: 03/07/2019
• Est. Priority Date: 09/05/2017
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: SAITO, Shinji, KAKUNO, Tsutomu, HASHIMOTO, Rei, KANEKO, Kei, KAI, Yasunobu
• Granted Patent: US 10,424,899 B2
• Time in Patent Office: Days
• CPC Class Codes: H01S 2302/02 THz - lasers, i.e. lasers with emission in the wavelength range of typically 0.1 mm to 1 mm
• CPC Class Codes: H01S 5/02469 Passive cooling, e.g. where heat is removed by the housing as a whole or by a heat pipe without any active cooling element like a TEC
• CPC Class Codes: H01S 5/028 Coatings ; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers
• CPC Class Codes: H01S 5/0425 Electrodes, e.g. characterised by the structure
• CPC Class Codes: H01S 5/04254 characterised by the shape
• CPC Class Codes: H01S 5/11 Comprising a photonic bandgap structure
• CPC Class Codes: H01S 5/1215 Multiplicity of periods
• CPC Class Codes: H01S 5/1225 with a varying coupling constant along the optical axis
• CPC Class Codes: H01S 5/18386 Details of the emission surface for influencing the near- or far-field, e.g. a grating on the surface
• CPC Class Codes: H01S 5/187 using Bragg reflection
• CPC Class Codes: H01S 5/305 characterised by the doping materials used in the laser structure
• CPC Class Codes: H01S 5/3402 intersubband lasers, e.g. transitions within the conduction or valence bands
• CPC Class Codes: H01S 5/34313 with a well layer having only As as V-compound, e.g. AlGaAs, InGaAs

Abstract

A surface emitting quantum cascade laser includes an active layer and a first semiconductor layer. The active layer includes a plurality of quantum well layers and is capable of emitting laser light by intersubband transition. The first surface includes an internal region and an outer peripheral region. Grating pitch of the first pits is m times grating pitch of the second pits. The outer peripheral region surrounds the internal region. A first planar shape of an opening end of the first pit is asymmetric with respect to a line passing through barycenter of the first planar shape and is parallel to at least one side of the first two-dimensional grating. A second planar shape of an opening end of the second pit is symmetric with respect to each of lines passing through barycenter of the second planar shape and is parallel to either side of the second two-dimensional grating.

Claims

1. A surface emitting quantum cascade laser comprising:

an active layer including a plurality of quantum well layers stacked therein and being capable of emitting laser light by intersubband transition; and

a first semiconductor layer provided on the active layer and having a first surface, the first surface including an internal region in which first pits constitute a first two-dimensional grating and an outer peripheral region in which second pits constitute a second two-dimensional grating, grating pitch of the first pits being m times (where m being an integer of 1 or more) grating pitch of the second pits, and the outer peripheral region surrounding the internal region,

a first planar shape of an opening end of the first pit being asymmetric with respect to a line passing through barycenter of the first planar shape and being parallel to at least one side of the first two-dimensional grating,

a second planar shape of an opening end of the second pit being symmetric with respect to each of lines passing through barycenter of the second planar shape and being parallel to either side of the second two-dimensional grating, and

the laser light having an emission wavelength corresponding to the grating pitch of the second pits and being emitted in a direction generally perpendicular to the active layer from the internal region.

2. The laser according to claim 1, wherein the grating pitch of the first pits is twice the grating pitch of the second pits.

3. The laser according to claim 1, further comprising:

an upper electrode provided on a portion of the internal region not provided with the first pits and a portion of the outer peripheral region not provided with the second pits;

a second semiconductor layer provided on a surface of the active layer on opposite side from a surface provided with the first semiconductor layer; and

a lower electrode provided on a surface of the second semiconductor layer on opposite side from the active layer side.

4. The laser according to claim 2, further comprising:

an upper electrode provided on a portion of the internal region not provided with the first pits and a portion of the outer peripheral region not provided with the second pits;

a second semiconductor layer provided on a surface of the active layer on opposite side from a surface provided with the first semiconductor layer; and

a lower electrode provided on a surface of the second semiconductor layer on opposite side from the active layer side.

5. The laser according to claim 1, wherein an inner surface of the first pit and an inner surface of the second pit are each covered with an insulator layer.

6. The laser according to claim 2, wherein an inner surface of the first pit and an inner surface of the second pit are each covered with an insulator layer.

7. The laser according to claim 3, wherein an inner surface of the first pit and an inner surface of the second pit are each covered with an insulator layer.

8. The laser according to claim 4, wherein an inner surface of the first pit and an inner surface of the second pit are each covered with an insulator layer.

9. The laser according to claim 5, wherein

a portion of the internal region not provided with the first pits and a surface of the insulator layer in the first pits are covered with the upper electrode, and a portion of the outer peripheral region not provided with the second pits and a surface of the insulator layer in the second pits are each covered with the upper electrode, and

the lower electrode is provided with an opening in a portion including part of the internal region in plan view.

10. The laser according to claim 1, wherein depth of the first pit is smaller than depth of the second pit.

11. The laser according to claim 9, wherein depth of the first pit reaches into the active layer.

12. The laser according to claim 10, wherein the depth of the first pit reaches into the active layer.

13. The laser according to claim 9, wherein depth of the second pit reaches into the active layer or penetrates through the active layer.

14. The laser according to claim 1, wherein the first pits do not overlap the second pits in plan view.

15. The laser according to claim 1, wherein the first planar shape includes a plurality of point-symmetric shapes.

16. The laser according to claim 1, wherein

the two-dimensional grating of the first pits is a square grating or a rectangular grating, and

the first planar shape of the opening end of the first pit is asymmetric with respect to a line passing through the barycenter of the first planar shape and being parallel to each of two sides of the first two-dimensional grating.

17. The laser according to claim 1, wherein the two-dimensional grating of the first pits is a regular triangular grating.