US-20260128569-A1 - VERTICAL-CAVITY SURFACE-EMITTING SEMICONDUCTOR LASER AND METHOD FOR PRODUCING A SEMICONDUCTOR LASER OF THIS TYPE

US20260128569A1US 20260128569 A1US20260128569 A1US 20260128569A1US-20260128569-A1

Abstract

A vertical-cavity surface-emitting semiconductor laser includes a semiconductor multi-layer structure in which a trench is formed, the trench running in a peripheral direction around a longitudinal center axis which runs perpendicularly to the semiconductor multi-layer structure and forming a mesa from the semiconductor multi-layer structure. The mesa contains a layer which is oxidized from an outer periphery of the mesa perpendicularly to the longitudinal center axis up to a predefined oxidation distance in order to form in the mesa an aperture for narrowing down an electrical and/or optical path. The trench has, in the peripheral direction around the longitudinal center axis, a plurality of portions in which the trench is closer to the longitudinal center axis than in other portions of the trench. The mesa has an inner mesa region and a plurality of support structures which surround the inner mesa region.

Inventors

Roman Koerner

Assignees

TRUMPF PHOTONIC COMPONENTS GMBH

Dates

Publication Date: 20260507
Application Date: 20251229
Priority Date: 20230706

Claims (14)

1 . A vertical-cavity surface-emitting semiconductor laser, comprising: a semiconductor multi-layer structure in which a trench is formed, the trench running in a peripheral direction around a longitudinal center axis which runs perpendicularly to the semiconductor multi-layer structure and forming a mesa from the semiconductor multi-layer structure, the mesa containing a layer which is oxidized from an outer periphery of the mesa perpendicularly to the longitudinal center axis up to a predefined oxidation distance in order to form in the mesa an aperture for narrowing down an electrical and/or optical path, wherein the trench has, in the peripheral direction around the longitudinal center axis, a plurality of portions in which the trench is closer to the longitudinal center axis than in other portions of the trench, wherein the mesa has an inner mesa region and a plurality of support structures which surround the inner mesa region, and wherein the aperture is located in the inner mesa region and the support structures are connected to the inner mesa region.
2 . The vertical-cavity surface-emitting semiconductor laser according to claim 1 , wherein at least a subset of the support structures have, in all dimensions in a plane parallel to the semiconductor multi-layer structure, dimensions which are less than twice the predefined oxidation distance of the oxidized layer.
3 . The vertical-cavity surface-emitting semiconductor laser according to claim 2 , wherein the support structures comprise first support structures which, in all dimensions in the plane parallel to the semiconductor multi-layer structure, have dimensions which are less than twice the predefined oxidation distance of the oxidized layer, and wherein the support structures have second support structures which, at least in one dimension in the plane parallel to the semiconductor multi-layer structure, have a dimension which is greater than twice the predefined oxidation distance of the oxidized layer.
4 . The vertical-cavity surface-emitting semiconductor laser according to claim 1 , wherein a portion of the oxidized layer located within at least a subset of the support structures is completely oxidized.
5 . The vertical-cavity surface-emitting semiconductor laser according to claim 1 , wherein at least a subset of the support structures have a surface metallization for electrical contacting of the semiconductor laser.
6 . The vertical-cavity surface-emitting semiconductor laser according to claim 5 , wherein the surface metallization is spatially limited to a relevant support structure or partially extends to the inner mesa region.
7 . The vertical-cavity surface-emitting semiconductor laser according to claim 1 , wherein at least four, at least six, or at least eight support structures of the support structures are formed which are distributed around the inner mesa region.
8 . The vertical-cavity surface-emitting semiconductor laser according to claim 1 , wherein the support structures form a support structure arrangement which is point-symmetrical with respect to the longitudinal center axis or mirror-symmetrical with respect to a plane parallel to the longitudinal center axis.
9 . The vertical-cavity surface-emitting semiconductor laser according to claim 1 , wherein at least a subset of the support structures are designed as elongate connecting elements in a radial direction with respect to the longitudinal center axis.
10 . The vertical-cavity surface-emitting semiconductor laser according to claim 1 , wherein at least a subset of the support structures are designed as columns.
11 . The vertical-cavity surface-emitting semiconductor laser according to claim 10 , wherein each column is connected to the inner mesa region via an elongate connecting element, wherein, in a plane perpendicular to the longitudinal center axis, the column has dimensions which are greater than a width of the connecting element.
12 . The vertical-cavity surface-emitting semiconductor laser according to claim 11 , wherein each connecting element tapers toward or away from the inner mesa region.
13 . The vertical-cavity surface-emitting semiconductor laser according to claim 1 , wherein the trench is widened in the region of the inner mesa region.
14 . A method for producing a vertical-cavity surface-emitting semiconductor laser, comprising the steps of: providing a semiconductor multi-layer structure, making a trench in the semiconductor multi-layer structure, wherein the trench runs in a peripheral direction around a longitudinal center axis which runs perpendicularly to the semiconductor multi-layer structure and forms a mesa from the semiconductor multi-layer structure, wherein the trench has, in the peripheral direction around the longitudinal center axis, a plurality of portions in which the trench is closer to the longitudinal center axis than in other portions of the trench, wherein the mesa has an inner mesa region and a plurality of support structures which surround the inner mesa region, and wherein the support structures are connected to the inner mesa region, oxidizing an oxidizable layer of the semiconductor multi-layer structure in order to form in the inner mesa region an aperture for narrowing down an electrical and/or optical path.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation of International Application No. PCT/EP2024/068778 (WO 2025/008426 A1), filed on July 3, 2024, and claims benefit to German Patent Application No. DE 102023117 883.0, filed on July 6, 2023. The aforementioned applications are hereby incorporated by reference herein. FIELD The invention relates to a vertical-cavity surface-emitting semiconductor laser, comprising a semiconductor multi-layer structure in which a trench is formed, the trench running in a peripheral direction around a longitudinal center axis which runs perpendicularly to the semiconductor multi-layer structure and forming a mesa from the semiconductor multi-layer structure, the mesa containing a layer which is oxidized from an outer periphery of the mesa perpendicularly to the longitudinal center axis up to a predefined distance in order to form in the mesa an aperture for narrowing down an electrical and/or optical path. BACKGROUND A semiconductor laser of this type is known from WO 2021/185697 A1. Vertical-cavity surface-emitting semiconductor lasers, or VCSELs for short, are used, for example, as radiation sources in sensor technology or in communications engineering. VCSELs typically have a semiconductor multi-layer structure in which semiconductor layers are grown epitaxially on a semiconductor substrate in a stacked arrangement. A semiconductor multi-layer structure of this type can have a first Bragg reflector, an active region, and a second Bragg reflector, 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 particular oxidation distance in order to form a current aperture and/or an optical aperture in the resonator, referred to in this description as an aperture. The semiconductor layer intended for oxidation is, for example, an Aluminum Arsenide (AIAs) layer that can be selectively oxidized to Aluminum Oxide (AI2O3) up to a particular oxidation distance. The predefined oxidation distance up to which said layer is oxidized is defined by the required aperture size and can be adjusted by the duration of the oxidation process. Prior to oxidation, a trench is made in the semiconductor multi-layer structure, for example by etching the semiconductor multi-layer structure from the upper face thereof. The trench typically has a depth of a few micrometers. The trench can be continuous or interrupted in the peripheral direction around the longitudinal center axis of the semiconductor multi-layer structure. The longitudinal center axis should be understood as the axis that passes through the center of the aperture and runs parallel to the stacking direction of the semiconductor multi-layer structure. The trench does not need to extend completely through the semiconductor multi-layer structure in the direction of the layer structure, but usually ends above the substrate. The trench forms a mesa in the semiconductor multi-layer structure, in which mesa the semiconductor layer to be oxidized is arranged. After the formation of the trench, the oxidation process can be carried out to oxidize the oxidizable layer, the oxidation starting from the outer periphery of the mesa and continuing until the aforementioned predefined oxidation distance is reached. Traditionally, VCSEL trenches are produced with a geometry that is square, rectangular, or round. A common problem with VCSELs is mechanical stress in the mesa, which can impair the functional reliability of the VCSEL, lead to VCSEL failure, or reduce the VCSEL's useful life. The mechanical stresses have various causes. One is that mechanical stresses are introduced into the mesa after oxidation to form the aperture, in particular when the oxidation distance is large. Another is that mechanical stresses can be induced in the mesa during the etching of the trench. Finally, the metallization on the upper face of the mesa for the electrical contacting of the VCSEL also contributes to mechanical stresses in the mesa. The above-mentioned document WO 2021/185697 A1 proposes that, after oxidation of the oxidizable layer, the oxidized outer peripheral region be removed and an electrically non-conductive material be inserted into the resulting gap in order to reduce the mechanical stresses in the mesa caused by the oxidation layer. However, this does not address all the causes of mechanical stress in the mesa. SUMMARY In an embodiment, the present disclosure provides a vertical-cavity surface-emitting semiconductor laser includes a semiconductor multi-layer structure in which a trench is formed, the trench running in a peripheral direction around a longitudinal center axis which runs perpendicularly to the semiconductor multi-layer structure and forming a mesa from the semiconductor multi-layer structure. The mesa contains a layer which is oxidized from an outer periphery of the mesa perpendicularly to the longitudinal c