Surface-emitting semiconductor laser having a vertical cavity and method for producing a semiconductor laser of this type

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).

Description

Surface-emitting semiconductor laser with vertical cavity and method for manufacturing such a laser

[0001] The invention relates to a surface-emitting semiconductor laser with a vertical cavity, comprising a semiconductor multilayer structure in which a trench is formed which extends circumferentially around a longitudinal central axis 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 to a predetermined width in order to form an aperture in the mesa for limiting 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, or VCSELs, are used, for example, as radiation sources in sensor technology and telecommunications. VCSELs typically have a multilayer semiconductor structure in which semiconductor layers are epitaxially grown on a semiconductor substrate in a stacked arrangement. Such a multilayer semiconductor structure may include a first Bragg mirror, an active region, and a second Bragg mirror, which together form an optical resonator. VCSELs also typically feature an oxidized region within the optical resonator, which consists of a semiconductor layer oxidized to a certain degree to form a current aperture and / or an optical aperture within the resonator, referred to here as the aperture.The semiconductor layer intended for oxidation is, for example, an AlAs layer, which can be selectively oxidized to Al₂O₃ up to a specific oxidation state. The predetermined oxidation state to which this layer is oxidized is determined by the required aperture size and can be adjusted by the duration of the oxidation process. Before oxidation, a groove is created in the semiconductor multilayer structure, for example, by etching the semiconductor multilayer structure. the top side of the semiconductor multilayer structure. The trench typically has a depth of a few micrometers. The trench can be continuous around the longitudinal center axis of the semiconductor multilayer structure or it can be interrupted. The longitudinal center axis is defined as the axis that passes centrally through the aperture and runs parallel to the stacking direction of the semiconductor multilayer structure. The trench does not necessarily have to extend completely through the semiconductor multilayer structure in the direction of the layer stacking, but usually ends above the substrate. The trench forms a mesa within the semiconductor multilayer structure, in which the semiconductor layer to be oxidized is located. After the trench has formed, the oxidation process can be carried out to oxidize the oxidizable layer, with the oxidation starting from the outer circumference of the mesa and proceeding until the predetermined oxidation depth mentioned above is reached.

[0004] Traditionally, VCSEL trenches are constructed with a geometry that is square, rectangular, or round.

[0005] A common problem with VCSELs is mechanical stress in the mesa, which can impair the VCSEL's reliability, lead to its failure, or reduce its lifespan. These 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 depth is large. Similarly, mechanical stresses can be induced in the mesa during the etching of the trench. Finally, the metallization on the top of the mesa, used for the VCSEL's electrical contacts, also contributes to mechanical stresses in the mesa.

[0006] The aforementioned document WO 2021 / 185697 A1 proposes removing the oxidized outer circumferential area after the oxidation of the oxidizable layer and inserting an electrically non-conductive material into the resulting gap to reduce the mechanical stresses in the mesa caused by the oxide layer. However, this does not address all the causes of 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 above, in which mechanical stresses in the mesa are further reduced or completely avoided.

[0008] Another task is to specify a method for producing such a VCSEL.

[0009] The problem mentioned first is solved 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 trench geometry of VCSELs. Viewed circumferentially around the longitudinal center axis, the trench of the VCSEL according to the invention has a plurality of sections in which the trench is arranged closer to the longitudinal center axis of the mesa than in the other sections of the trench. This results in the mesa being formed with an inner mesa region and a plurality of support structures, or alternatively, an inner mesa region and a plurality of support structures surrounding the inner mesa region. The aperture (current and / or optical confinement) is arranged in the inner mesa region, and the support structures are connected to the inner mesa region. The inner mesa region and the support structures are formed from the semiconductor multilayer structure.In other words, the trench is positioned section by section closer to the center of the mesa, which in this case is defined by the aforementioned longitudinal axis, and section by section further away from the center of the mesa in order to form support structures for the inner mesa region. This achieves several advantages. Firstly, the oxidation depth is reduced because the dimensions of the inner mesa region perpendicular to the longitudinal axis are smaller in the sections where the trench is positioned closer to the longitudinal axis. Another advantage is that the geometry of the trench according to the invention forms support structures in the mesa that surround the inner mesa region and thus mechanically support it. Furthermore, the support structures can transfer mechanical stresses from the inner mesa region outwards into the support structures, i.e., "absorb" them. There is yet another advantage. The advantage lies in the fact that one or more metallizations required for the electrical contacting of the VCSEL can be arranged on the support structures instead of on the inner mesa region, thereby also reducing or even eliminating mechanical stresses in the inner mesa region. Overall, the VCSEL according to the invention therefore has the advantage that mechanical stresses in the inner mesa region, which serves for light generation and emission, are significantly reduced, thus significantly increasing the functional reliability and service life of the VCSEL, or significantly reducing its susceptibility to failure.

[0011] In the aforementioned document WO 2021 / 185697 A1, support structures are described for a preliminary stage of the VCSEL during its manufacture; however, these are removed before the VCSEL is completed and are no longer present in the finished VCSEL. The VCSEL according to the invention, however, is a finished VCSEL in which the support structures remain after its manufacture.

[0012] Preferably, support structures of at least a subset of the support structures have dimensions in all dimensions in a plane parallel to the semiconductor multilayer structure or perpendicular to the longitudinal central axis that are smaller than twice the oxidation width of the oxidized layer.

[0013] A key advantage here is that when the oxidizable layer of the semiconductor multilayer structure is oxidized to form the aperture, this layer, which is also present in the support structures, is completely oxidized within the support structures. This makes these support structures particularly suitable for applying a metallization for electrical contacting the VCSEL. The current flow from the respective metallization then passes directly into the inner mesa region via the connection between this support and the inner mesa region, while short-circuit current paths from the metallization perpendicularly through the semiconductor layers of the support structure are avoided. The metallization can be limited to the top surface of the respective support structure or extend partially, for example, to an outer edge of the inner mesa region. Through-hole plating from the metallization to the inner mesa region via vias is also possible.

[0014] All support structures in the plane parallel to the semiconductor multilayer structure can also be dimensioned such that they are smaller than twice the oxidation width of the oxidized layer.

[0015] In a further preferred embodiment, the support structures comprise first support structures which, in all dimensions in a plane parallel to the semiconductor multilayer structure, have dimensions that are smaller than twice the oxidation width of the oxidized layer, and the support structures comprise second support structures which, at least in one dimension in a plane parallel to the semiconductor multilayer structure, have a dimension that is larger than twice the oxidation width of the partially oxidized layer.

[0016] In this configuration, the trench thus forms at least two types of support structures. The combination of first and second support structures has the advantage that the "thinner" support structures can absorb stresses better because they are more flexible, while the second support structures, which are "thicker" and not oxidized through due to their larger dimensions, exhibit higher mechanical stability. While the first support structures may have a metallized surface on their upper surface because they are oxidized through, the second support structures, on the other hand, will not have a metallized surface because they are not oxidized through. The first and second support structures can be arranged alternately around the inner mesa region.

[0017] As described above, it is advantageous if an area of ​​the oxidized layer located within at least a subset of the support structures is completely oxidized.

[0018] Likewise, as already described above, it is advantageous if at least a subset of the support structures, preferably support structures in which the area of ​​the oxidized layer is completely oxidized, has a surface metallization for electrical contacting of the semiconductor laser.

[0019] The metallization can be spatially limited to the respective support or extend partially to the inner mesa area, e.g. to an edge thereof.

[0020] In the first case, where the metallization is spatially confined to the respective support, current flow from the metallization can be achieved via the semiconductor connection of the support to the inner mesa region, or via vias to a deeper layer with an additional metallization layer. If the metallization extends partially onto the inner mesa region, current flow from the metallization to the inner mesa region is reliably ensured. The portion of the metallization located on the inner mesa region can be significantly smaller in size than the portion of the metallization located on the support structure.

[0021] Preferably, at least four, at least six or at least eight supporting structures are formed around the inner mesa area.

[0022] With a larger number of support structures, which can be correspondingly smaller in the plane parallel to the semiconductor multilayer structure, mechanical stresses from the inner mesa region can be absorbed particularly well by the support structures. In particular, a larger number of support structures allows for better absorption of mechanical stresses in different directions, since the support structures can be arranged at smaller angular intervals around the inner mesa region as their number increases.

[0023] Furthermore, it is preferred if the support structures form a support structure arrangement that is point-symmetric with respect to the longitudinal center axis of the inner mesa region or mirror-symmetric with respect to a plane parallel to the longitudinal center axis of the inner mesa region. Since the center of the inner mesa region is the location of greatest mechanical stresses, it is advantageous to select a support structure arrangement that is point-symmetric with respect to the center of the inner mesa region in order to direct the mechanical stresses radially symmetrically outwards from the center of the inner mesa region.

[0024] Preferably, support structures of at least a subset of the support structures are designed as elongated webs in the radial direction with respect to the longitudinal center axis, and / or support structures of at least a subset of the support structures are designed as columns.

[0025] Bridges have the advantage of being narrow and therefore more flexible in absorbing stress. The bridges can also be described as suspension points for the inner mesa. The bridges can be so narrow that the oxidizable layer within them is completely oxidized. In contrast, columns, which can have, for example, a rectangular, square, or circular outer circumference, offer improved mechanical support for the inner mesa. Column-type and bridge-type support structures can be arranged around the inner mesa in an alternating pattern.

[0026] An advantageous combination of webs and columns consists of connecting the respective column to the inner mesa area via an elongated web. In this design, the advantages of a column-shaped support structure (mechanical stability) and a web-shaped support structure (stress absorption) are combined.

[0027] It can be advantageous if the respective bridge tapers towards or away from the inner mesa area.

[0028] This is advantageous if the bridge has a width greater than twice the oxidation width of the oxidized layer, so that through-oxidation is ensured in the narrower tapered section of the bridge, thereby avoiding short-circuit current paths in the bridge.

[0029] Furthermore, in a preferred embodiment, the trench is provided to be wider in the area of ​​the inner mesa area than in the area of ​​the support structures.

[0030] This design is particularly advantageous in the case where a large number of small or narrow support structures are to be formed by the trench. Widening the trench around the inner measuring area allows for more "free-standing" support structures, particularly enabling a star-shaped geometry of the support structure arrangement. Especially when the support structures consist of a combination of columns and webs, the webs can also be tapered, as such a support structure arrangement facilitates good dissipation of mechanical stresses from the inner mesa area while also ensuring a smaller footprint for current flow, thus minimizing the capacitance of the inner mesa area.

[0031] The widened trench can also serve as an improved heat sink close to the inner mesa area, for example by filling the trench with gold plating.

[0032] Furthermore, according to the invention, a method for producing a surface-emitting semiconductor laser with a vertical cavity is provided according to claim 15.

[0033] In the method according to the invention, a trench with a geometry as described above with regard to the VCSEL according to the invention is introduced into the semiconductor multilayer structure, and wherein, after the introduction of the trench, an oxidizable layer of the semiconductor multilayer structure is oxidized in order to form the aperture in the inner mesa region for limiting an electrical and / or optical path in the inner mesa region.

[0034] The support structures created by the trench are either completely oxidized or only partially oxidized, as described above, depending on the dimensions of the support structures in a plane parallel to the semiconductor multilayer structure.

[0035] The method according to the invention has the same advantages as the VCSEL according to the invention.

[0036] The introduction of the trench into the semiconductor multilayer structure can be carried out by any suitable etching process known in the field of VCSEL fabrication.

[0037] For the purposes of the present invention, a "trench" is understood to be a trench which is bounded on both sides by a wall made of the semiconductor multilayer structure or only by a wall, in the latter case by the outer wall of the mesa.

[0038] Further advantages and features will become apparent from the following description and the attached drawing.

[0039] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0040] Exemplary embodiments of the invention are shown in the drawing and are described in more detail below with reference to them. The drawing shows: Fig. 1 a schematic top view of a vertical cavity surface-emitting semiconductor laser (VCSEL); Fig. 2 shows a section through the VCSEL in Fig. 1 along line 11-11 in Fig. 1; Fig. 3 shows a section through the VCSEL in Fig. 1 along a line III-III in Fig. 1; Fig. 4 shows a schematic top view of another VCSEL; Fig. 5 shows a schematic top view of another VCSEL; Fig. 6 shows a schematic top view of another VCSEL; Fig. 7 shows a schematic top view of another VCSEL; Fig. 8 shows a schematic top view of another VCSEL; Fig. 9 shows a schematic top view of another VCSEL; Fig. 10 shows a schematic top view of another VCSEL; and Fig. 11 shows a schematic top view of another VCSEL.

[0041] Figures 1 to 11 show various embodiments of a vertical cavity surface-emitting semiconductor laser (VCSEL). It should be noted that the VCSELs and their structural features are not shown to scale.

[0042] Figures 1 to 3 show a first VCSEL 10. The VCSEL 10 has a semiconductor multilayer structure 12. The semiconductor multilayer structure can be constructed in the manner typical for VCSELs. Details of the semiconductor multilayer structure 12 are not relevant for understanding the present invention and are therefore not described here. For example, the semiconductor multilayer structure 12 can be arranged on a substrate (not shown). Starting from the substrate, the semiconductor multilayer structure 12 can have a first Bragg mirror, an active zone, and a second Bragg mirror, as well as electrical contacts for applying a drive current to the VCSEL.

[0043] In the semiconductor multilayer structure 12, a groove 14 is formed that extends circumferentially around a longitudinal central axis 16 of the semiconductor multilayer structure 12. The longitudinal central axis 16 is an axis that runs centrally through the semiconductor multilayer structure 12, or the VCSEL 10, perpendicular to the individual layers of the semiconductor multilayer structure 12. In other words, the longitudinal central axis 16 runs in the stacking direction of the individual semiconductor layers of the semiconductor multilayer structure 12.

[0044] In the embodiment shown in Figures 1 to 3 and the subsequent figures, the trench 14 is shown as a trench extending continuously around the longitudinal center axis 16. However, the trench 14 can also have interruptions in the circumferential direction around the longitudinal center axis.

[0045] Typically, the trench 14 has a depth T of a few micrometers. In the embodiment shown in Figures 1 to 3, the trench 14 separates a first (outer) region from a second (inner) region 20. In this configuration, the trench 14 thus has a first (outer) wall 22 and a second (inner) wall 24. It is understood, however, that the trench 14 can only be bounded on one side by a wall, namely wall 24, so that, in other words, the first region 18 of the semiconductor multilayer structure 12 is missing.

[0046] The trench 14 can be created by an etching process commonly used in the fabrication of VCSELs. Due to the trench, the second (inner) region 20 of the semiconductor multilayer structure is formed as a mesa 26.

[0047] A layer 28 is arranged in the mesa 26. This layer is oxidized from the outer perimeter of the mesa 26, i.e., the wall 24, perpendicular to the longitudinal central axis 16, to a predetermined oxidation depth W, in order to form an aperture OA in the mesa 26 for delimiting an electrical and / or optical path. Before oxidation, the layer 28 is a readily oxidizable layer of the semiconductor multilayer structure 12, for example, an AlAs layer. After the trench 14 was created, the semiconductor multilayer structure 12 was exposed to an oxidation atmosphere, which oxidized the layer 28 from the wall 24 to the predetermined oxidation depth W. The oxidation depth W is determined by the duration of the oxidation process. The central region of the layer 28 remains unoxidized and defines the aperture OA.Since in the illustrated embodiment the layer 28 extends into the first region 18, the layer 28 is also oxidized in the first region 18 up to the oxidation range, as indicated by section 28a.

[0048] The trench 14 has a plurality of sections 30 circumferentially around the longitudinal center axis 16, with the trench 14 in Fig. 1 having a total of four such sections 30 in which the trench 14 is arranged closer to the longitudinal center axis 16 than in the other sections 32. Due to this geometry of the trench 14, an inner mesa region 34 is formed within the mesa 26, and a plurality of support structures 36 surround the inner mesa region 34. In the illustrated embodiment, four support structures 36 are formed. The aperture OA is arranged in the inner mesa region 34. The support structures 36 are connected to the inner mesa region 34 via narrow connecting sections 38. The support structures 36 together with the connecting sections 38 are formed from the same semiconductor multilayer structure 12 as the inner mesa region 34.Due to the sections 30 of the trench 14 being located closer to the longitudinal center axis 16, the oxidation path for producing the aperture OA is advantageously shortened compared to conventional VCSELs. This allows the oxidation process to be shorter and also reduces mechanical stresses in the inner mesa region 34 due to the shorter oxidation length or reduced oxidation width W. Furthermore, the geometry of the sections 30 of the trench 14 located closer to the longitudinal center axis 16 allows the shape of the aperture OA to be shaped as desired. In Fig. 1, the four sections 30 together essentially form a square, so that the aperture OA is also correspondingly square.

[0049] A desired geometry of the trench 14 can be specified by a suitably designed etching mask when etching the trench 14.

[0050] The support structures 36 increase the mechanical stability of the inner mesa region 34. The support structures 36 can also transfer mechanical stresses from the inner mesa region 34 into the support structures 36. The support structures 36 can be described as extensions of the inner mesa region 34.

[0051] In the embodiment according to Figs. 1 to 3, the support points in all dimensions in a plane parallel to the layers of the semiconductor multilayer structure 12 have dimensions Ds (Fig. 3) that are smaller than twice the oxidation width W of the oxidized layer 28. In the embodiment shown in Figs. 1 to 3, the support points- The support structures 36 are approximately square in shape. The four side lengths of the support structures 36 are thus less than or equal to twice the oxidation width W. This ensures that the support structures 36 are completely oxidized during the oxidation process for producing the aperture OA, as shown in Fig. 3 with section 28b of layer 28 in the support structure 36. Due to the complete oxidation of layer 28 in the support structures, no current flow through the support structures 36 in the direction of a double arrow 39 in Fig. 3 is possible. This can, in turn, be advantageously used to provide the support structures 36 on their upper surface with a metallization 40, which serves for the electrical contacting of the VCSEL 10. For example, a p-contact of the VCSEL is realized with the metallization 40. Preferably, a metallization 40 is provided on each of the support structures 36.Current can flow from the metallizations 40 on the support structures 36 via the connecting sections 38 into the inner mesa region 34 and there through the aperture OA. The metallizations 40 can be limited to the support structures 36, or, as shown in Fig. 1 with a metallization extension 40a, they can extend to the edge region of the inner mesa region 34.

[0052] If the metallizations 40 do not extend into the inner mesa region 34, this has the advantage of mechanically decoupling the metallizations 40 from the inner mesa region 34, thereby further reducing mechanical stresses in the inner mesa region 34 caused by the metallizations. If the metallizations 40 are limited to the support structures 36, these can be connected to the inner mesa region 34 via a single through-hole connection using vias and an additional metallization.

[0053] In a process for fabricating the VCSEL 10, a trench 14 with the geometry described above is introduced into the semiconductor multilayer structure 12. The trench is introduced into the semiconductor multilayer structure 12 by a suitable etching process using an etch mask designed according to the geometry of the trench 14 to be produced. After the trench 14 has been introduced, layer 28 of the semiconductor multilayer structure is oxidized to form the aperture OA in the inner mesa region 34, thus defining an electrical and / or optical path within that region. The layer 28 in the support structures 36 is thereby Completely oxidized. The metallizations 40 are applied to the support structures 36.

[0054] With reference to Figures 4 to 11, further embodiments of each VCSEL are described. Only the differences compared to VCSEL 10 in Figures 1 to 3 are described. For all other details, reference is made to the description of the embodiment of VCSEL 10 in Figures 1 to 3. Furthermore, the same reference numerals are used in Figures 4 to 11 as in Figures 1 to 3, insofar as they denote identical, similar, or comparable elements of VCSELs 10 in Figures 4 to 11.

[0055] In the VCSEL 10 shown in Fig. 4, the sections 30 of the trench 14, which are arranged closer to the longitudinal center axis 16 than the sections 32 of the trench 14, are semicircular. This results in a circular inner mesa area 34, as well as a circular aperture OA. As mentioned above, the geometry of the sections 30 determines not only the shape of the inner mesa area 34, but also the shape of the aperture OA.

[0056] In the embodiment shown in Fig. 4, the sections 30 of the trench 14, which are closer to the longitudinal center axis 16 than the other sections 32 of the trench 14, have a meandering shape, thereby forming additional support structures 36a besides the support structures 36. The support structures 36a, in turn, have dimensions in all dimensions in a plane parallel to the semiconductor multilayer structure 12 that are smaller than twice the oxidation width W of layer 28 (as described above with reference to Fig. 1). This makes it possible to provide the additional support structures 36a with metallizations 40b on their upper surface, since, like the support structures 36, the additional support structures 36a do not form short-circuit current paths through them.

[0057] While the embodiments in Figs. 1 to 4 have a total of four support structures 36, the embodiment in Fig. 5 has a total of eight support structures 36, 36a. The support structures 36 in Figs. 1 to 4 each form a support structure arrangement that is point-symmetrical with respect to the longitudinal center axis 16 and also symmetrical with respect to a The plane containing the longitudinal center axis 16 is mirror-symmetric. The support structures 36, 36a of the VCSEL 10 in Fig. 5 also form a point-symmetric or mirror-symmetric arrangement of support structures, as do the embodiments to be described in Figs. 6 to 11.

[0058] Fig. 6 shows an embodiment of a VCSEL 10 in which the trench 14 has a geometry that forms an inner mesa region 34 and support structures 36b in the semiconductor multilayer structure 12, the support structures 36b being designed as elongated webs. The aperture OA is not shown in Fig. 6, but it is present in the inner mesa region 34 as in the previous embodiments. In Fig. 6, the inner mesa region 34 is circular, as in Fig. 4, as is the aperture OA (not shown). The support structures 36b from the semiconductor multilayer structure 12 have such dimensions that the layer 28 is completely oxidized in the support structures 36b. Accordingly, the support structures 36b can be provided with metallizations 40 for electrical contacting the VCSEL 10. The embodiment in Fig.6 is advantageous with respect to the symmetry of the support structures 36b around the center of the inner mesa region 34, since mechanical stresses from the inner mesa region 34 are transferred radially symmetrically into the support structures 36b, as illustrated by arrows 46. Due to the geometry of the support structures 36b as elongated webs, they are particularly suitable for absorbing stresses.

[0059] Figure 7 shows an embodiment of a VCSEL 10, which is a modification of the embodiment in Figure 6. In the embodiment of the VCSEL 10 in Figure 7, the trench 14 forms two types of support structures. First, there are the support structures 36b as in Figure 6, which carry metallizations 40 on their upper surface. Second, there are support structures 36c, which, similar to the embodiments in Figures 1 to 5, are formed as columns. However, unlike the support structures 36 in Figures 1 to 5, these 36c have a dimension in at least one dimension parallel to the plane of the semiconductor multilayer structure 12 that is greater than twice the oxidation width W. Therefore, in the columnar support structures 36c, the layer 28 is not completely oxidized, as indicated by the dashed lines 48.This is harmless with regard to a possible current path through the support structures 36c, since the support structures 36c do not have any metallization on their upper surface. They also do not serve to contact the VCSEL 10. The columnar support structures 36c are connected to the inner mesa region 34 by rib-shaped support structures 36d, which in turn are so narrow that the layer 28 of the semiconductor multilayer structure 12 is completely oxidized within these rib-shaped support structures 36d. The advantage of the larger columnar support structures 36c is their greater mechanical stability; that is, they act, so to speak, as support columns in the outer area of ​​the mesa 26.

[0060] Fig. 8 shows a modification of the VCSEL 10 in Fig. 7, according to which the web-shaped support structures 36d, which connect the column-shaped support structures 36c to the inner mesa region 34, are widened, so that the support structures 36d also possess higher mechanical stability. Due to the widening of the support structures 36d by more than twice the oxidation width W, the layer 28 in the region of the support structures 36d is not fully oxidized, as indicated by the dashed lines, which, however, is harmless since the support structures 36c and 36d do not exhibit metallization on their upper surface.

[0061] Furthermore, it is possible for the web-like support structures connecting the column-shaped support structures 36c to the inner mesa region 34 to widen from the inner mesa region 34 to the column-shaped support structures 36c, as shown with a web-like support structure 36e in Fig. 8. The advantage here is that, in addition to increased mechanical stability due to a greater web width of the support structure 36e, through-oxidation of the layer 28 in the support structure 36e and thus insulation is enabled. The embodiment in Fig. 8 is characterized by a very small oxidation zone, low ohmic resistance due to metallizations 40 on the support structures 36b brought close to the inner mesa region 34, and high mechanical stability due to additional column-shaped support structures 36c.

[0062] Figures 9 to 11 show further embodiments of VCSELs 10, which have in common that the trench 14 in the region of the inner mesa area 34 has a width DG in a plane parallel to the layers of the semiconductor multilayer structure 12 or perpendicular to the longitudinal central axis 16, which is greater than the width of the respective trench 14 in Figure 1. 1 to 8. In the embodiments shown in Figs. 9 to 11, the trench 14 is further designed such that narrower and longer web-shaped support structures 36d are formed, which can correspondingly dissipate more stress from the inner mesa area 34. Due to the small dimensions of the web-shaped support structures 36d and the column-shaped support structures 36c, the layer 28 in these support structures can be completely oxidized, so that all column-shaped support structures 36c, and optionally also the support structures 36d, can be provided with metallizations 40 on their upper surface. In the embodiment shown in Fig. 10, the web-shaped support structures 36d are even narrower than in the embodiment shown in Fig. 9. In the embodiment shown in Fig. 11, the web-shaped support structures 36d taper towards the column-shaped support structures 36c, thus, as in the embodiment shown in Fig.10 ensures good discharge of stresses from the inner mesa region 34, and also allows for a smaller footprint for current conduction, so that no excessively large mesa capacitance is generated. The embodiment in Fig. 11 resembles a star-shaped geometry of the inner mesa region 34 with the support structures 36d and 36c.

[0063] Additionally, in the embodiments shown in Figs. 9 to 11, the trench can be filled with a gold plating, thereby increasing the metallic heat sink close to the inner mesa area 34.

Claims

Patent claims 1 . A surface-emitting semiconductor laser with a vertical cavity, comprising 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 layer 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 sections 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 area (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. A 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. Surface-emitting semiconductor laser with a vertical cavity according to claim 1 or 2, wherein the support structures comprise 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 comprise second support structures (36b; 36d) which, at least in 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. 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. A vertical cavity surface emitting semiconductor laser according to any 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 portion of the oxidized layer (28) is completely oxidized, has a surface metallization (40; 40a) for electrically contacting the semiconductor laser (10).

6. A vertical cavity surface emitting semiconductor laser 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. A vertical cavity surface emitting semiconductor laser according to any 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. A vertical cavity surface emitting semiconductor laser according to any 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. A vertical cavity surface emitting semiconductor laser according to any one of the preceding claims, wherein support structures (36b; 36d; 36e) of at least a subset of the support structures are formed as elongated webs in the radial direction relative to the longitudinal central axis (16).

10. A vertical cavity surface emitting semiconductor laser according to any 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 formed as columns.

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. 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. A vertical cavity surface emitting semiconductor laser according to any one of the preceding claims, wherein the trench (14) is widened in the region of the inner mesa region (34).

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 sections 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) surrounding 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.

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