Search

EP-4740278-A1 - SURFACE-EMITTING SEMICONDUCTOR LASER HAVING A VERTICAL CAVITY AND METHOD FOR PRODUCING A SEMICONDUCTOR LASER OF THIS TYPE

EP4740278A1EP 4740278 A1EP4740278 A1EP 4740278A1EP-4740278-A1

Abstract

A surface-emitting semiconductor laser having a vertical cavity comprises a semiconductor multi-layer structure (12) in which a trench (14) is formed, the trench running in a peripheral direction around a longitudinal center axis (16) which runs perpendicularly to the semiconductor multi-layer structure and forming a mesa (26) from the semiconductor multi-layer structure (12). The mesa (26) contains a layer (28) which is oxidized from an outer periphery of the mesa perpendicularly to the longitudinal center axis up to a predefined oxidation distance (W) in order to form in the mesa (26) an aperture (OA) for narrowing down an electrical and/or optical path. The trench (14) has, in the peripheral direction around the longitudinal center axis (16), a plurality of portions (30) in which the trench (14) is closer to the longitudinal center axis (16) than in the other portions (32) of the trench (14), the mesa (26) thus having an inner mesa region (34) and a plurality of support structures (36; 36a; 36b; 36c; 36d; 36e) which surround the inner mesa region (34), the aperture (OA) being located in the inner mesa region (34) and the support structures (36; 36a; 36b; 36c; 36d; 36e) being connected to the inner mesa region (34).

Inventors

  • KOERNER, Roman

Assignees

  • TRUMPF Photonic Components GmbH

Dates

Publication Date
20260513
Application Date
20240703

Claims (14)

  1. 1 . Surface-emitting semiconductor laser with a vertical cavity, with a semiconductor multilayer structure (12) in which a trench (14) is formed, which runs in the circumferential direction around a longitudinal central axis (16) running perpendicular to the semiconductor multilayer structure and forms a mesa (26) from the semiconductor multilayer structure (12), wherein a layer (28) is arranged in the mesa (26) which is oxidized from an outer circumference of the mesa perpendicular to the longitudinal central axis up to a predetermined oxidation width (W) in order to form an aperture (OA) in the mesa (26) for delimiting an electrical and/or optical path, characterized in that the trench (14) has a plurality of sections (30) in the circumferential direction around the longitudinal central axis (16), in which the trench (14) is arranged closer to the longitudinal central axis (16) than in the remaining sections (32) of the trench (14), whereby the mesa (26) has an inner Mesa region (34) and a plurality of support structures (36; 36a; 36b; 36c; 36d; 36e) surrounding the inner mesa region (34), wherein the aperture (OA) is arranged in the inner mesa region (34) and the support structures (36; 36a; 36b; 36c; 36d; 36e) are connected to the inner mesa region (34).
  2. 2. Vertical cavity surface emitting semiconductor laser according to claim 1, wherein support structures (36; 36a; 36b; 36c; 36d; 36e) of at least a subset of the support structures have dimensions (Ds) in all dimensions in a plane parallel to the semiconductor multilayer structure (12) that are smaller than twice the oxidation width (W) of the oxidized layer (28).
  3. 3. Surface-emitting semiconductor laser with vertical cavity according to claim 1 or 2, wherein the support structures have first support structures (36b) which in all dimensions in a plane parallel to the semiconductor multilayer structure (12) have dimensions which are smaller than twice the oxidation width (W) of the oxidized layer (28), and wherein the support structures have second support structures (36b; 36d) which in at least one dimension in a plane parallel to the semiconductor multilayer structure (12) have a dimension which is greater than twice the oxidation width (W) of the oxidized layer (28).
  4. 4. A vertical cavity surface emitting semiconductor laser according to any one of claims 1 to 3, wherein a portion (28a) of the oxidized layer (28) located within at least a subset of the support structures (36) is completely oxidized.
  5. 5. Surface-emitting semiconductor laser with a vertical cavity according to one of claims 1 to 4, wherein at least a subset of the support structures (36; 36a; 36b; 36c; 36d; 36e), preferably support structures (36; 36a; 36b; 36c; 36d; 36e) in which a section of the oxidized layer (28) is completely oxidized, has a surface metallization (40; 40a) for electrically contacting the semiconductor laser (10).
  6. 6. Surface-emitting semiconductor laser with a vertical cavity according to claim 5, wherein the metallization (40; 40a) is spatially limited to the respective support structure (36; 36a; 36b; 36c; 36d; 36e) or extends partially to the inner mesa region (34).
  7. 7. Vertical cavity surface emitting semiconductor laser according to one of the preceding claims, wherein at least four, at least six or at least eight support structures (36; 36a; 36b; 36c; 36d; 36e) are formed which are arranged distributed around the inner mesa region (34).
  8. 8. Vertical cavity surface emitting semiconductor laser according to one of the preceding claims, wherein the support structures (36; 36a; 36b; 36c; 36d; 36e) form a support structure arrangement which is point-symmetrical with respect to the longitudinal central axis (16) or mirror-symmetrical with respect to a plane parallel to the longitudinal central axis (16).
  9. 9. Surface-emitting semiconductor laser with a vertical cavity according to one of the preceding claims, wherein support structures (36b; 36d; 36e) of at least a subset of the support structures are designed as elongated webs in the radial direction with respect to the longitudinal central axis (16).
  10. 10. Vertical cavity surface emitting semiconductor laser according to one of the preceding claims, wherein support structures (30; 30c) of at least a subset of the support structures (36; 36a; 36b; 36c; 36d; 36e) are designed as columns.
  11. 11. A vertical cavity surface emitting semiconductor laser according to claim 10, wherein the respective column is connected to the inner mesa region (34) via an elongated web (36d), the column having dimensions in a plane perpendicular to the longitudinal central axis (16) that are greater than a width of the web.
  12. 12. A vertical cavity surface emitting semiconductor laser according to claim 9 or 11, wherein the respective ridge tapers towards or away from the inner mesa region (34).
  13. 13. Vertical cavity surface emitting semiconductor laser according to one of the preceding claims, wherein the trench (14) is widened in the region of the inner mesa region (34).
  14. 14. A method for producing a surface-emitting semiconductor laser (10) with a vertical cavity, comprising the steps: Providing a semiconductor multilayer structure (12), Introducing a trench (14) into the semiconductor multilayer structure (12), wherein the trench (14) extends in the circumferential direction around a longitudinal central axis (16) running perpendicular to the semiconductor multilayer structure (12) and a mesa (26) of the semiconductor multilayer structure (12), wherein the trench (14) has a plurality of sections (30) in the circumferential direction around the longitudinal central axis (16), in which the trench (14) is arranged closer to the longitudinal central axis (16) than in the remaining sections (32) of the trench (14), whereby the mesa (26) is formed with an inner mesa region (34) and a plurality of support structures (36; 36a; 36b; 36c; 36d; 36e) which surround the inner mesa region (34), wherein the support structures (36; 36a; 36b; 36c; 36d; 36e) are connected to the inner mesa region (34), Oxidizing an oxidizable layer (28) of the semiconductor multilayer structure (28) to form an aperture (OA) in the inner mesa region (34) for defining an electrical and/or optical path.

Description

Vertical cavity surface emitting semiconductor laser and method for producing such a laser [0001] The invention relates to a surface-emitting semiconductor laser with a vertical cavity, with a semiconductor multilayer structure in which a trench is formed which runs in the circumferential direction around a longitudinal central axis running perpendicular to the semiconductor multilayer structure and forms a mesa from the semiconductor multilayer structure, wherein a layer is arranged in the mesa which is oxidized from an outer circumference of the mesa perpendicular to the longitudinal central axis up to a predetermined width in order to form an aperture in the mesa for delimiting an electrical and/or optical path. [0002] Such a semiconductor laser is known from WO 2021/185697 A1. [0003] Vertical cavity surface emitting semiconductor lasers, abbreviated to VCSEL (Vertical Cavity Surface Emitting Laser), are used, for example, as radiation sources in sensor technology or in communications technology. VCSELs typically have a semiconductor multilayer structure in which semiconductor layers are grown epitaxially on a semiconductor substrate in a stack arrangement. Such a semiconductor multilayer structure can have a first Bragg mirror, an active region and a second Bragg mirror, which together form an optical resonator. VCSELs typically also have an oxidized region in the optical resonator, which has a semiconductor layer that is oxidized up to a certain oxidation width in order to form a current aperture and/or an optical aperture in the resonator, which is abbreviated to an aperture in the present description. The semiconductor layer intended for oxidation is, for example, an AlAs layer, which can be specifically oxidized to Al2O3 up to a certain oxidation width. The predetermined oxidation width to which this layer is oxidized is determined by the size of the aperture to be achieved and can be adjusted by the duration of the oxidation process. Before oxidation, a trench is introduced into the semiconductor multilayer structure, for example by etching the semiconductor multilayer structure from its top side. The trench typically has a depth of a few micrometers. The trench can be continuous in the circumferential direction around the longitudinal center axis of the semiconductor multilayer structure, but can also be interrupted. The longitudinal center axis is to be understood as the axis that passes through the center of the aperture and runs parallel to the stacking direction of the semiconductor multilayer structure. The trench does not have to pass completely through the semiconductor multilayer structure in the direction of the layer structure, but usually ends above the substrate. The trench forms a mesa in the semiconductor multilayer structure in which the semiconductor layer to be oxidized is arranged. After the trench has been formed, the oxidation process for oxidizing the oxidizable layer can be carried out, with the oxidation starting from the outer circumference of the mesa and being carried out up to the predetermined oxidation width mentioned above. [0004] Traditionally, the trenches of VCSELs are manufactured with a geometry that is square, rectangular or round. [0005] A common problem with VCSELs is mechanical stresses in the mesa, which can affect the functional reliability of the VCSEL, lead to a failure of the VCSEL or reduce the lifetime of the VCSEL. The mechanical stresses have various causes. One cause is that mechanical stresses are introduced into the mesa after oxidation to form the aperture, especially if the oxidation width is large. Mechanical stresses can also be induced into the mesa when the trench is etched. Finally, the metallization on the top of the mesa for the electrical contacting of the VCSEL also contributes to mechanical stresses in the mesa. [0006] In the above-mentioned document WO 2021/185697 A1, it is proposed to remove the oxidized outer peripheral region after the oxidizable layer has been oxidized and to introduce an electrically non-conductive material into the resulting gap in order to reduce the mechanical stresses in the mesa caused by the oxidation layer. However, this does not combat all causes of the mechanical stresses in the mesa. [0007] Against this background, it is an object of the present invention to provide a surface-emitting semiconductor laser with a vertical cavity of the type mentioned at the outset, in which mechanical stresses in the mesa are even more reduced or completely avoided. [0008] It is a further object to provide a method for producing such a VCSEL. [0009] The first-mentioned object is achieved by a surface-emitting semiconductor laser with a vertical cavity according to claim 1. [0010] The VCSEL according to the invention has a trench whose geometry differs from the usual geometry of trenches of VCSELs. The trench of the VCSEL according to the invention has, viewed in the circumferential direction around the longitudinal cent