Laser comprising a distributed Bragg mirror and production method thereof
A laser includes a distributed Bragg mirror and is configured to emit monochromatic light radiation along a longitudinal direction. The laser has layers, stacked along a first transverse direction normal to the longitudinal direction and made of III-V materials, including an active region configured to emit the radiation. The mirror is formed by periodic lateral corrugations which extend mainly along the longitudinal direction and having a dimension along a second transverse direction normal to the longitudinal direction. The lateral corrugations of the Bragg mirror extend from a top surface of the waveguide pattern along the first transverse direction on a height strictly less than the depth, at which the active region is located starting from the top surface, such that a portion of lateral flanks of the waveguide is free of any lateral corrugations at the active region.
1. A laser comprising a distributed Bragg mirror,
said laser being configured to emit light radiation along a longitudinal direction and comprising a waveguide formed at least in part in a stack of layers made of III-V materials, said waveguide comprising at least one active region configured to emit said light radiation, said stack having a top surface, the at least one active region being located at a depth h a measured along a first transverse direction perpendicular to the longitudinal direction and from the top surface, and
said Bragg mirror comprising lateral corrugations distributed periodically along a longitudinal direction in a period A, said lateral corrugations being carried by at least one lateral flank of the waveguide parallel to a lateral plane defined by the longitudinal direction and the first transverse direction, said lateral corrugations having a height h′ along the first transverse direction and a dimension d along a second transverse direction perpendicular to the longitudinal direction, wherein
the lateral corrugations of the Bragg mirror extend from the top surface of the stack into a first layer of the stack made of a first one of the III-V materials, and the height h′ of the lateral corrugations is strictly less than the depth h a ,
a second layer of the stack made of a second one of the III-V materials different from the first layer has a top surface in direct contact with the first layer and is formed over the active region,
a portion of the at least one lateral flank of the waveguide is free of any lateral corrugations, said portion being located at the at least one active region and at the second layer.
2. The laser according to claim 1 wherein the lateral corrugations of the Bragg mirror are distributed and designed such that d/Λ>1.
3. The laser according to claim 1 wherein
the second layer comprises at least one optical confinement layer located above the at least one active region, at a depth h c along the first transverse direction from the top surface, and
the portion of the at least one lateral flank of the waveguide is free of any lateral corrugations at said optical confinement layer.
4. The laser according to claim 1 wherein the lateral corrugations are located from the at least one active region by a distance h a −h′ along the first transverse direction, h a −h′ being greater than or equal to 200 nm.
5. The laser according to claim 1 wherein the height h′ of the lateral corrugations of the Bragg mirror is greater than or equal to 500 nm.
6. The laser according to claim 1 further comprising a top electrode arranged on the top surface of the waveguide.
7. The laser according to claim 6 wherein the top electrode comprises a top portion covering the top surface of the waveguide and at least one lateral portion covering and formed in the lateral corrugations.
8. The laser according to claim 7 wherein the at least one lateral portion of the top electrode has metal corrugations covering the lateral corrugations of the Bragg mirror.
9. The laser according to claim 1 wherein the laser is a quantum cascade laser.
10. A method for forming a laser comprising a distributed Bragg mirror, comprising:
providing a stack of layers made of III-V materials comprising at least one active region for emitting light radiation,
forming a waveguide pattern in the stack of layers, said waveguide pattern having a length L along a longitudinal direction, a height h along a first transverse direction and a width w along a second transverse direction, the first and second transverse directions being normal to the longitudinal direction, said waveguide pattern having a top surface and lateral flanks extending parallel to a lateral plane defined by the longitudinal direction and the first transverse direction, and
structuring said waveguide pattern so as to form lateral corrugations at said lateral flanks, said lateral corrugations being periodic with period A along the longitudinal direction and having a dimension d along the second transverse direction, and at least partly forming the distributed Bragg mirror,
wherein the structuring is configured such that:
the lateral corrugations of the Bragg mirror extend from the top surface of the waveguide pattern into a first layer of the stack made of a first one of the III-V materials along the first transverse direction to a height h′ strictly less than a depth h a , at which the at least one active region is located starting from the top surface of the waveguide pattern,
a second layer of the stack made of a second one of the III-V materials different from the first layer has a top surface in direct contact with the first layer and is formed over the active region, and
a portion of the lateral flanks of the waveguide is free of any lateral corrugations at the at least one active region and at the second layer.
11. The method according to claim 10 comprising providing the stack with a stopping layer located above the at least one active region, wherein the structuring of the lateral corrugations is configured such that the lateral corrugations do not extend beyond said stopping layer along the first transverse direction, said stopping layer being located at a depth substantially equal to h′ with respect to the top surface of the waveguide pattern.
12. The method according to claim 11 wherein the stopping layer is InGaAs-based and has a thickness of between 20 nm and 200 nm.
13. The method according to claim 10 further comprising forming a top electrode pattern that is at least partly on the top surface of the waveguide pattern.
14. The method according to claim 13 wherein forming the top electrode pattern comprises depositing a metal layer on the top surface and in the lateral corrugations, and structuring said metal layer, such that said top electrode pattern has a top portion covering the top surface of the waveguide and at least one lateral portion covering the lateral corrugations.
15. The method according to claim 14 comprising structuring the metal layer such that the at least one lateral portion of the electrode pattern has lateral flanks that are parallel to the lateral plane and free of any lateral corrugations.
16. The method according to claim 14 comprising structuring the metal layer such that the at least one lateral portion of the electrode pattern has metal corrugations covering the lateral corrugations.
17. The laser according to claim 3 wherein the at least one optical confinement layer is InGaAs-based.
18. The laser according to claim 1 wherein each of the second layer and the active region has lateral sides opposing the lateral corrugations of the first layer and each lateral side is free of any lateral corrugations.