Win-guided semiconductor laser and manufacturing process therefor

Abstract

Gain-guided semiconductor laser (1) with a semiconductor layer sequence (2) and with electrical contact surfaces (4), wherein - the semiconductor layer sequence (2) comprises an active zone (21) for generating radiation, at least one waveguide layer (22) at the active zone (21) and at least one cladding layer (23) at the at least one waveguide layer (22), - the semiconductor layer sequence (2) further comprises at least one current aperture layer (3) which is electrically conductive along a resonator axis (R) of the semiconductor laser (1) in a central region (32) and electrically insulating in edge regions (33) directly adjoining the central region (32), - perpendicular to the resonator axis (R) the central region (32) has a width (W) of at least 20 µm and the edge regions (33) each have at least a minimum width (M), - the minimum width (M) is 3 µm or more, and - viewed from above, the semiconductor layer sequence (2) and the electrical contact surfaces (4) in the central region (32) and at least up to the minimum width (M) in the direction transverse to the resonator axis (R) on one side of the current aperture layer (3) facing away from the active zone (21) are components extending on both sides beyond the central region (32), - a trench (5) extends on both sides along the resonator axis (3) and the trenches (5) laterally expose the current-aperture layer (3) and cut through the entire semiconductor layer sequence (2) down to a substrate (6), and - the trenches (5) are designed to suppress parasitic modes, such that the trenches (5) each have a cross-section with two side surfaces inclined to a growth direction (G) of the semiconductor layer sequence (2).

Description

[0001] A gain-guided semiconductor laser is specified. Furthermore, a manufacturing method for such a semiconductor laser is specified.

[0002] The documents WO 01 / 50553 A2 and WO 02 / 49168 A2 relate to edge-emitting semiconductor lasers with a ridge waveguide, wherein a current aperture layer is incorporated into the ridge waveguide.

[0003] From the document DE 10 2017 112 242 A1, a gain-guided semiconductor laser is known which has strain layers that specifically generate strains in a semiconductor layer sequence.

[0004] The document US 6 195 380 B1 concerns a laser diode for DVDs (digital versatile disks).

[0005] The document DE 199 63 807 A1 describes a stripe laser diode element.

[0006] The document DE 102 08 463 A1 describes a semiconductor laser device.

[0007] The document US 2005 / 0 121 682 A1 describes a semiconductor laser with a heat sink.

[0008] The document DE 100 61 701 A1 relates to a semiconductor laser with lateral current conduction.

[0009] One task to be solved is to provide a gain-guided semiconductor laser that exhibits a high optical quality of an emitted laser mode.

[0010] This object is achieved by a semiconductor laser and a manufacturing method having the features of the independent patent claims. Preferred developments are the subject of the dependent claims.

[0011] The semiconductor laser is a gain-guided semiconductor laser. This means that mode guidance in the direction perpendicular to a resonator axis is not achieved by refractive index jumps, such as those caused by ridge waveguides or refractive index jumps. Instead, the beam guidance of laser radiation within the semiconductor laser is defined by the current flow area of ​​an active zone. Thus, a semiconductor layer sequence in the region of the resonator axis, viewed from above, is geometrically unstructured and formed by continuous layers without any optically significant inhomogeneities.

[0012] The semiconductor laser comprises a semiconductor layer sequence. The semiconductor layer sequence includes at least one active zone for generating radiation and thus for generating laser radiation.

[0013] Furthermore, the semiconductor layer sequence comprises one or, preferably, two waveguide layers. The at least one waveguide layer is located at the active zone, preferably directly at the active zone. The waveguide layer, especially together with the active zone, has a comparatively high optical refractive index for the laser radiation, so that waves can be guided in the waveguide layer in a direction parallel to a growth direction of the semiconductor layer sequence.

[0014] The semiconductor layer sequence also includes one or, preferably, two cladding layers. The at least one cladding layer is located on the associated waveguide layer. It is possible for at least one cladding layer to be located directly on the associated waveguide layer. The at least one cladding layer has a comparatively low refractive index compared to the associated waveguide layer in order to enable waveguiding of the laser radiation.

[0015] The semiconductor layer sequence is preferably based on a III-V compound semiconductor material. The semiconductor material is, for example, a nitride compound semiconductor material such as Al n In 1-n-m Ga m N or a phosphide compound semiconductor material such as Al n In 1-n-m Ga m P or an arsenide compound semiconductor material such as Al n In 1-n-m Ga m Ace or like Al n Gam In 1-n-m Ace k P 1-k , where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and n + m ≤ 1 as well as 0 ≤ k < 1. Preferably, for at least one layer or for all layers of the semiconductor layer sequence, 0 < n ≤ 0.8, 0.4 ≤ m < 1 and n + m ≤ 0.95 as well as 0 < k ≤ 0.5 apply. The semiconductor layer sequence can comprise dopants as well as additional components. For the sake of simplicity, however, only the essential components of the crystal lattice of the semiconductor layer sequence, i.e. Al, As, Ga, In, N or P, are given, even if these can be partially replaced and / or supplemented by small amounts of other substances.

[0016] Preferably, the semiconductor layer sequence is based on the material system Al n In 1-n-m Ga m As, or AlInGaAs for short.

[0017] The semiconductor layer sequence also comprises one or more current aperture layers. The at least one current aperture layer has electrically conductive properties in a central region along the resonator axis of the semiconductor laser and electrically insulating properties in peripheral regions. Thus, during normal operation of the semiconductor laser, current flows only through the current aperture layer in the central region. The current aperture layer is thus configured to define a current-carrying region of the active zone. The resonator axis is thus also defined via the current aperture layer.

[0018] The central region has a width of at least 20 µm or 50 µm, or preferably at least 100 µm, in the transverse direction, particularly in the direction perpendicular to the resonator axis. This means that the central region, and thus the energized area of ​​the active zone, is comparatively wide. The semiconductor laser is thus a broad-area laser.

[0019] The edge regions immediately following the central region in the direction away from the resonator axis each have at least a minimum width. This means that the width of the edge regions can be equal to the minimum width, or the edge regions can have a width that is greater than the minimum width.

[0020] The minimum width is at least 3 µm or 5 µm. According to at least one embodiment, the minimum width is at most 100 µm, 50 µm, 20 µm, or 10 µm. Preferably, the minimum width is between 5 µm and 10 µm.

[0021] The semiconductor layer sequence comprises electrical contact surfaces. The electrical contact surfaces are configured for direct current injection into the semiconductor layer sequence. The electrical contact surfaces are preferably composed of one or more metal layers, with layers of a transparent conductive oxide optionally also being present. However, the electrical contact surfaces are preferably metallic structures. In particular, the active zone, and especially a current-carrying region of the active zone, is located between the electrical contact surfaces.

[0022] Viewed from above, the electrical contact surfaces and the semiconductor layer sequence are continuous components in an optically relevant region. The optically relevant region, viewed from above, is primarily the central region and, on either side of the central region, a strip extending beyond the central region, at least up to the minimum width, in a direction perpendicular to the resonator axis.

[0023] This means that there are no optically relevant geometric edges and / or structures in the central region and in the strips with a width of at least the minimum width. In other words, the semiconductor layer sequence and the electrical contact surfaces, or at least one electrical contact surface directly on the semiconductor layer sequence, are flat, unstructured structures across the central region and across strips with a width of at least the minimum width.

[0024] The fact that the semiconductor layer sequence and the electrical contact surfaces in the central region and extending beyond it on both sides at least up to the minimum width are unstructured and continuous components preferably applies in at least one cross-section perpendicular to the resonator axis and parallel to the growth direction of the semiconductor layer sequence. In particular, this applies to all cross-sections perpendicular to the resonator axis in a region of at least 80% or 90% of the length of the resonator axis. Deviations from this geometry are possible at resonator ends, particularly if the electrical contact surface is not present at the resonator ends.

[0025] The gain-guided semiconductor laser comprises a semiconductor layer sequence and electrical contact surfaces. The semiconductor layer sequence comprises an active zone for generating radiation, at least one waveguide layer at the active zone, and at least one cladding layer at the at least one waveguide layer. The semiconductor layer sequence comprises at least one current diaphragm layer, which is electrically conductive in a central region along a resonator axis of the semiconductor laser and electrically insulating in adjacent edge regions. Transverse to the resonator axis, the central region has a width of at least 20 µm, and the edge regions have at least a minimum width. The minimum width is 3 µm or more.Viewed from above, the semiconductor layer sequence and at least the electrical contact area on the semiconductor layer sequence are continuous components in the central region and on both sides, at least up to the minimum width in the direction transverse to the resonator axis, adjoining the central region and extending beyond the central region. In particular, a trench extends along both sides of the resonator axis, and the trenches laterally expose the current shield layer and sever the entire semiconductor layer sequence down to a substrate. The trenches are specifically designed to suppress parasitic modes, so that the trenches have side surfaces that extend obliquely to a growth direction of the semiconductor layer sequence.

[0026] Viewed in plan view, the semiconductor layer sequence and the electrical contact surfaces in the central region and at least up to the minimum width in the direction transverse to the resonator axis on a side of the current aperture layer facing away from the active zone are continuous components on both sides extending beyond the central region.

[0027] The processing of a current injection, particularly on a p-type side of infrared broad-area lasers, by structuring highly conductive p-GaAs, for example, and subsequent deposition of strained dielectrics and / or metals, leads to increased strain in p-type semiconductor layers near structural edges, such as at the edges of a structured p-GaAs layer. Since GaAs and AlGaAs become birefringent under pressure and thus under strain, the electro-optical properties of the laser in question are also affected.

[0028] On the one hand, this means that the radiation angle in the horizontal plane, i.e., in the direction perpendicular to the growth direction of the semiconductor layer sequence, also known as slow axis divergence, is impaired. On the other hand, this means that birefringence can cause polarization rotation just below structural edges, resulting in laser light at the edge of a broad-area emitter being more strongly TM-polarized. This is problematic for many applications.

[0029] In the gain-guided semiconductor laser described here, which is specifically designed as a broad-area laser, structural edges and thus strains are avoided in an energized region generating laser radiation. This allows the radiation angle to be controlled in a plane perpendicular to a growth direction of the semiconductor layer sequence, and birefringence at the edges of an energized region intended for laser radiation generation can be avoided or at least significantly reduced.

[0030] In the semiconductor laser described here, this is achieved in particular by avoiding structural edges on a surface of the semiconductor layer sequence, thus preventing stress increases at such edges. Furthermore, the optical amplification is gain-guided, with the width of the current spreading, and thus the gain-guided width, being essentially current-independent, which leads to more stable electro-optical properties.

[0031] For this purpose, a selectively oxidizable epitaxially grown layer, i.e., the current-shielding layer, is integrated into the semiconductor layer sequence. Such layers are known, for example, from vertically emitting lasers, but in such lasers they serve to confine an emitting region. In lasers with index guidance, especially with ridge waveguides, current-confining layers can be used to achieve single-mode operation.

[0032] In lasers with ridge waveguides, however, the electrically insulating edge regions of a current aperture layer are comparatively narrow, as otherwise index guidance would no longer be ensured due to the ridge waveguide. In contrast, the current aperture layer of the semiconductor laser described here has a comparatively large edge width, so that the edge regions are particularly wide enough to shield optical modes supported in the semiconductor laser from structures located outside the edge regions.

[0033] This means that in semiconductor lasers with ridge waveguides, the edge regions of a current gate layer must be so narrow that an optical mode can bridge the electrically insulating edge regions due to index guidance. The exact opposite is true for the semiconductor laser described here.

[0034] According to at least one embodiment, trenches extend along the resonator axis on both sides and along the resonator axis. This means that, viewed from above, the resonator axis is located between two trenches. The trenches preferably extend along the entire resonator axis. The current shield layer is exposed laterally through the trenches.

[0035] The trenches cut through the active zone and the entire semiconductor layer sequence, for example, up to or even into a substrate, in particular a growth substrate for the semiconductor layer sequence. This means that the active zone can have the same width as the current aperture layer, and the current aperture layer and the active zone can be congruent or essentially congruent when viewed from above. Essentially means, for example, with a tolerance of at most 1 µm, 0.5 µm, or 0.2 µm. In semiconductor lasers with a ridge waveguide structure, however, the active zone is usually located beneath a ridge waveguide and thus has a greater width than the ridge waveguide itself.

[0036] According to at least one embodiment, the current aperture layer is located between the waveguide layer and the associated cladding layer, or between one of the waveguide layers and the associated cladding layer. If two current aperture layers are present, a corresponding current aperture layer can be arranged between the associated waveguide layer and the associated cladding layer.

[0037] Alternatively, the current aperture layer is located in the cladding layer or on a side of the cladding layer facing away from the active zone. Preferably, however, the current aperture layer is attached to a side of the cladding layer facing the active zone. It is also possible for the current aperture layer to be located in the waveguide layer.

[0038] According to at least one embodiment, the distance between the current aperture layer and the active zone is at least 0.5 µm or 0.8 µm. Alternatively or additionally, this distance is at most 2 µm or 1.5 µm. In particular, the current aperture layer is approximately 1 µm away from the active zone.

[0039] According to at least one embodiment, the current aperture layer has a small thickness. This means, in particular, that the thickness of the current aperture layer is at least 1 nm, 10 nm, or 15 nm. Alternatively or additionally, the thickness of the current aperture layer is at most 100 nm, 70 nm, or 50 nm.

[0040] According to at least one embodiment, the current shield layer is formed from a III-V semiconductor material in the central region. In the edge regions, the current shield layer comprises one or more III-oxides, in particular aluminum oxide and / or gallium oxide.

[0041] According to at least one embodiment, the current shield layer has a different average thickness in the central region than in the edge regions. However, the difference in thickness between the central region and the edge regions is preferably only slight. In particular, this difference in thickness is at most 3%, 2%, or 1% of the average thickness of the central region. For example, this difference in thickness is at least 0.1% or 0.3% of the average thickness of the central region.

[0042] According to at least one embodiment, the semiconductor layer sequence is based on the material system AlInGaAs, in particular AlGaAs, so that no indium is present. The current aperture layer is preferably made of Al in the central region. 1-z Ga zAs. Here, z is preferably greater than or equal to 0.005 or greater than or equal to 0.01. Alternatively or additionally, z is at most 0.05, 0.03, or 0.025. Thus, the current aperture layer in the central region is essentially made of AlAs with only a small Ga content.

[0043] According to at least one embodiment, layers of the semiconductor layer sequence directly adjacent to the current aperture layer have an aluminum content of at least 5%, 10%, 20%, and / or of at most 60%, 40%, or 50%. Such layers adjacent to the semiconductor layer sequence are made, in particular, of AlInGaAs or AlGaAs. These layers can represent the cladding layers and / or the waveguide layers.

[0044] According to at least one embodiment, the semiconductor laser has facets. The facets are configured to reflect and / or couple out laser radiation generated during operation. The facets are preferably created by cleaving the semiconductor layer sequence. It is possible for passivation layers and / or layers for adjusting reflectivity to be present on the facets.

[0045] According to at least one embodiment, the facets are free of electrically insulating regions of the current aperture layer at least in a radiation outcoupling region. In the radiation outcoupling region, the generated laser radiation exits the facets.

[0046] According to at least one embodiment, the edge regions of the current aperture layer extend along the resonator axis in the semiconductor layer sequence with a constant width. Alternatively, it is possible for an edge region of the current aperture layer to also be present at the facets, so that no current is supplied to the active zone directly at the facets.

[0047] Preferably, however, the facet in the central region is free of an electrically insulating region of the current aperture layer, so that a possible current release of the active zone at the facets can be achieved in particular by a geometry of the electrical contact surfaces.

[0048] According to at least one embodiment, the width of the edge regions of the current shield layer is equal to the minimum width. This preferably applies with a tolerance of at most 1 µm, 0.5 µm, or 0.2 µm. This means that the electrical contact surfaces can be laterally flush with the semiconductor layer sequence. The electrical contact surfaces, or at least one of the electrical contact surfaces directly adjacent to the semiconductor layer sequence, as well as the semiconductor layers, can extend congruently or approximately congruently when viewed from above.

[0049] According to at least one embodiment, a width of the edge regions is greater than the minimum width. This means that the semiconductor layer sequence is then wider than at least one of the electrical contact areas, in particular wider than the electrical contact area directly at the semiconductor layer sequence.

[0050] According to at least one embodiment, the semiconductor laser comprises precisely one current aperture layer. The current aperture layer is then preferably located in a p-conducting region of the semiconductor layer sequence. This means that the current aperture layer can be located between the active zone and the electrical contact area configured as the anode.

[0051] According to at least one embodiment, the semiconductor laser comprises exactly two of the current aperture layers. The active zone is located between the current aperture layers. Thus, one of the current aperture layers lies in a p-conducting region of the semiconductor layer sequence, and the other of the current aperture layers lies in an n-conducting region of the semiconductor layer sequence.

[0052] According to at least one embodiment, an emission wavelength or wavelength of maximum intensity of the laser radiation generated by the semiconductor laser during operation is at least 830 nm or 840 nm and / or at most 1.1 µm or 1060 nm. In other words, the semiconductor laser then emits near-infrared radiation during operation.

[0053] According to at least one embodiment, the semiconductor laser is configured for multimode operation.

[0054] In summary, the combination of structural edge avoidance and current-independent current expansion due to the current aperture layer makes it possible to improve the electro-optical properties of the infrared-emitting, gain-guided broad-area laser described here.

[0055] Furthermore, a manufacturing method is specified. Using the manufacturing method, a semiconductor laser is manufactured according to one or more of the above-mentioned embodiments. Features of the manufacturing method are therefore also disclosed for the semiconductor laser, and vice versa.

[0056] In at least one embodiment, the method comprises the following steps, preferably in the order given: - epitaxial growth of the semiconductor layer sequence including the current aperture layer, - Creating the trenches on both sides along the resonator axis so that the current aperture layer is exposed laterally, - oxidising the exposed current aperture layer starting from the trenches so that the electrically insulating edge regions are formed and so that the non-oxidised, immediately adjacent regions of the current aperture layer form the electrically conductive central region, - Applying the electrical contact surfaces, and - Separation to the semiconductor lasers, particularly by means of scribing and breaking.

[0057] According to at least one embodiment, the oxidation of the current aperture layer is carried out wet-chemically.

[0058] According to at least one embodiment, the oxidation of the current shield layer is carried out at a temperature of at least 300°C or 350°C. Alternatively or additionally, this temperature is at most 600°C, 500°C, or 450°C.

[0059] A semiconductor laser described herein and a manufacturing method described herein are explained in more detail below with reference to the drawings using exemplary embodiments. Like reference numerals indicate like elements in the individual figures. However, they are not drawn to scale; rather, individual elements may be exaggerated for clarity.

[0060] They show: Fig. 1 a schematic sectional view of a process step for producing a semiconductor laser described here, Fig. 2 a schematic sectional view of a process step for producing a semiconductor laser described here, Fig. 3 a schematic plan view of a process step for producing a semiconductor laser described here, Fig. 4 a schematic sectional view of an embodiment of a semiconductor laser described here, Fig. 5 a schematic sectional view of an embodiment of a semiconductor laser described here, Fig. 6 a schematic sectional view of an example with partial aspects of a semiconductor laser described here, Fig. 7 is a schematic plan view of an embodiment of a semiconductor laser described here, and Fig. 8 is a schematic sectional view of a modification of a semiconductor laser.

[0061] In the Fig. 1 to 4, a manufacturing method for a semiconductor laser 1 is illustrated. According to Fig. 1, a semiconductor layer sequence 2 is grown on a substrate 6. The substrate 6 is, for example, an n-doped GaAs substrate. A growth layer 27 is optionally located directly on the substrate 6.

[0062] Along a growth direction G, the semiconductor layer sequence 2 comprises a cladding layer 23, a waveguide layer 22, an active zone 21, a further waveguide layer 22, and a further cladding layer 23. All of these layers can be made of AlGaAs and are, for example, n-doped on the substrate side and p-doped on a side facing away from the active zone 21.

[0063] Towards the substrate 6 or the optional growth layer 27, the semiconductor layer sequence 2 can have a buffer layer 25. The buffer layer 25 is made of n-doped GaAs, for example. Furthermore, the semiconductor layer sequence can have a contact layer 24 on a side facing away from the substrate 6. The contact layer 24 can form a top side 20 of the semiconductor layer sequence. For example, the contact layer 24 is made of p-doped GaAs, in which case a relatively high dopant concentration can be present.

[0064] The semiconductor layer sequence 2 also includes a current aperture layer 3. The current aperture layer 3 is preferably located between the p-side waveguide layer 22 and the associated cladding layer 23 and directly borders these layers. Like all other layers of the semiconductor layer sequence 2, the current aperture layer 3 is preferably grown as a homogeneous, continuous, and unstructured layer across an entire wafer.

[0065] For example, the current aperture layer 3 is made of p-doped AlGaAs with a Ga content of 2%. This means that the current aperture layer 3 is almost entirely made of AlAs. The thickness of the current aperture layer 3 is preferably only small, in particular around 30 nm. In contrast, the distance between the current aperture layer 3 and the active zone 21 is relatively large, for example, approximately 1 µm.

[0066] In the process step of Fig. 2 illustrates that trenches 5 are formed through the semiconductor layer sequence 2 into the growth substrate 6. The trenches 5 can be V-shaped in cross section. The Fig. 1, the current shield layer 3 grown laterally is exposed, as can also apply to all other layers of the semiconductor layer sequence 2. A width of the trenches 5 on the upper side 20 is, for example, at least 2 µm or 5 µm and / or at most 20 µm or 10 µm, in particular between 5 µm and 10 µm inclusive.

[0067] After the trenches 5 have been formed, the current aperture layer 3 is oxidized laterally from the trenches 5. This oxidation is preferably carried out wet-chemically at a temperature of, for example, approximately 400°C. The oxidation forms edge regions 33 that extend away from the trenches 5 toward a non-oxidized central region 32. In the central region 32, the current aperture layer 3 remains electrically conductive. In the oxidized edge regions 33, however, the current aperture layer 3 is electrically insulating or at least significantly reduced in its electrical conductivity. A transition between the edge regions 33 and the central region 32 in the lateral direction is preferably abrupt.

[0068] In Fig. 3 is a plan view of the wafer after the process steps of Fig. 2. The trenches 5 preferably extend continuously along the later resonator axes of the isolated semiconductor lasers 1. The trenches 5 can thus be formed on the wafer by straight, continuous structures across several of the later semiconductor lasers 1. Thus, two of the trenches 5 are preferably located between adjacent regions of the semiconductor layer sequence 2 for the semiconductor lasers 1.

[0069] The trenches 5 in the finished semiconductor lasers 1 are designed to suppress parasitic modes such as ring modes. As a result, the trenches 5 have side surfaces that extend obliquely to the growth direction G in order to reflect radiation not intended for amplification away from the plane of the active zone 21.

[0070] In Fig. 4 shows the finished semiconductor laser 1, after which electrical contact surfaces 4 have been applied and after which the semiconductor lasers 1 have been separated, for example by means of slits to create facets. As in Fig. 2 is a resonator axis perpendicular to the plane of the Fig. 4 oriented.

[0071] The electrical contact area 4 on the upper side 20 of the semiconductor layer sequence 2 is applied comparatively broadly across the semiconductor layer sequence 2. Thus, structural edges in the area of ​​the energized central region 32 are avoided. Thus, no or no significant strains of the semiconductor layer sequence 2, which would be caused by structural edges, occur at the central region 32. Thus, a high quality of the optical modes of the emitted laser radiation can be achieved.

[0072] A width W of the central region 32 is preferably at least 100 µm and is thus comparatively wide. An unstructured minimum width M, which adjoins the central region 32 on both sides, is preferably between 5 µm and 10 µm inclusive. Thus, the minimum width M is large enough that optical decoupling away from the central region 32 occurs across the minimum width M. In other words, the minimum width M is selected to be large enough that structures outside the minimum width M no longer have a significant optical influence on the guided laser mode.

[0073] According to Fig. 4, the edge regions 33 are wider than the minimum width M. This means that the semiconductor layer sequence 2 projects beyond the contact area 4 on the upper side 20. The contact area 4 on the substrate 6 is preferably applied over the entire area or almost over the entire area. The contact areas 4 are each formed, for example, by a layer stack comprising several metallic layers. Since the contact areas 4 are applied over a comparatively large area, positive charge carriers h and negative charge carriers e are also impressed over a relatively large area in the direction of the active zone 21. A concentration of the charge carriers e, h occurs due to the current aperture layer 3, which is only sufficiently electrically conductive in the central area 32.

[0074] In the example of Fig. 5 illustrates that a passivation 8 is additionally applied in the trenches 5. The passivation 8 can partially cover the semiconductor layer sequence 2 on the upper side 20.

[0075] It is possible for the contact area 4 on the upper side 20 to partially extend onto the passivation 8. This creates an edge 9 between the corresponding contact area 4 and the passivation 8. However, this edge 9 is spaced at least a minimum width M from the central region 32, in the direction perpendicular to the growth direction G and in the direction perpendicular to a resonator axis R, which runs perpendicular to the plane of the drawing (not shown). Stresses in the semiconductor layer sequence 2 caused by the edge 9 are thus far enough away from the central region 32 to still exert an influence on the generation of the laser radiation.

[0076] Deviating from the representation in Fig. 5, it is possible that the contact surface 4 on the upper side 20 ends flush with the passivation 8 in the lateral direction or that this contact surface 4 ends at a distance from the passivation 8.

[0077] In the example of Fig. 6 shows that the semiconductor layer sequence 2 and the contact surface 4 are flush with each other on the upper side 20. The same can also be seen in the embodiments of Fig. 4 and Fig. 5. In addition, according to Fig. 6 optionally the passivation 8 may be present.

[0078] Furthermore, Fig. Figure 6 illustrates that an additional current aperture layer 3 may optionally be present. This means that the active zone 21 may be located between the two current aperture layers 3.

[0079] The trenches 5 can be designed trapezoidally widening towards the substrate 6 when viewed in cross section. Furthermore, it is possible that the trenches 5 do not extend into the substrate 6. Deviating from claim 1, in Fig. 6 an etching stop layer 28 is present in the semiconductor layer sequence 2, for example directly on the substrate 6.

[0080] In Fig. Figure 7 shows a plan view of the semiconductor laser 1. It can be seen that the trenches 5 extend on both sides of a resonator axis R. The edge regions 33 originate from the trenches 5 and extend with a constant width along the entire resonator axis R and thus directly along the central region 32. The resonator axis R is delimited by facets 7. At one of the facets 7, laser radiation L generated during operation emerges from the semiconductor layer sequence 2.

[0081] Unlike in Fig. 7, the contact surface 4 can end at the top 20 at a distance from the facets 7 in order to prevent or reduce current supply directly to the facets 7.

[0082] In Fig. 8 shows a modification 10 of a semiconductor laser. In this modification 10, no current shield layer is present. Lateral current limitation is achieved via the geometry of the passivation layer 8 and / or the contact layer 4. Thus, the edges 9, viewed from above onto the top side 20, are located directly at a current-carrying region of the active zone 21, in Fig. 8 is schematically indicated by an ellipse. These edges 9 create strains in the semiconductor layer sequence 2 directly at the energized area. This can cause a change in the polarization of the laser radiation at the edges of the energized zone. This is undesirable in many applications.

[0083] By dividing the current aperture layer 3 into the central region 32 and the edge regions 33, stresses are also induced in the semiconductor layer sequence 2, but due to the small thickness, these stresses have only a small, negligible influence.

[0084] Furthermore, the current aperture layer 3 is so thin that, due to the division of the current aperture layer 3 into the central region 32 and the edge regions 33, there is effectively no index guidance of the laser mode; instead, only pure gain guidance is present. However, this gain guidance is more stable because the proximity of the current aperture layer 3 to the active zone 21 makes current expansion virtually independent of the current intensity. Without the current aperture layer 3, however, increasing current intensity leads to an increasing expansion and enlargement of the energized area, which influences the emitted laser mode.

[0085] The components shown in the figures preferably follow one another directly in the specified order, unless otherwise indicated. Layers that do not touch in the figures are preferably spaced apart from one another. Where lines are drawn parallel to one another, the corresponding surfaces are preferably also aligned parallel to one another. Likewise, unless otherwise indicated, the relative positions of the drawn components to one another are correctly represented in the figures.

[0086] This patent application claims priority from German patent application 10 2018 123 019.2, the disclosure of which is hereby incorporated by reference.

[0087] The invention described here is not limited by the description based on the exemplary embodiments. Rather, the invention encompasses any novel feature and any combination of features, including in particular any combination of features in the patent claims, even if this feature or combination itself is not explicitly stated in the patent claims or exemplary embodiments. List of reference symbols 1 semiconductor laser 2 Semiconductor layer sequence 20 Top side of the semiconductor layer sequence 21 active zone 22 waveguide layer 23 Sheath layer 24 Contact layer 25 Buffer layer 27 Growth layer 28 Etch stop layer 3 current aperture layer 32 Central Area 33 Marginal area 4 electrical contact surface 5 ditch 6 Substrat 7 facets 8 Passivation 9 edge 10 Modification of a semiconductor laser e, h charge carriers G Growth direction L Laser radiation M Minimum width of the edge areas R Resonator axis W Width of the central area

Claims

[1] Gain-guided semiconductor laser (1) with a semiconductor layer sequence (2) and with electrical contact surfaces (4), wherein - the semiconductor layer sequence (2) comprises an active zone (21) for generating radiation, at least one waveguide layer (22) on the active zone (21) and at least one cladding layer (23) on the at least one waveguide layer (22), - the semiconductor layer sequence (2) further comprises at least one current diaphragm layer (3) which is electrically conductive in a central region (32) along a resonator axis (R) of the semiconductor laser (1) and electrically insulating in edge regions (33) directly adjoining the central region (32), - transversely to the resonator axis (R), the central region (32) has a width (W) of at least 20 µm and the edge regions (33) each have at least a minimum width (M), - the minimum width (M) is 3 µm or more, and - viewed in plan view, the semiconductor layer sequence (2) and the electrical contact surfaces (4) in the central region (32) and at least up to the minimum width (M) in the direction transverse to the resonator axis (R) on a side of the current aperture layer (3) facing away from the active zone (21) are continuous components on both sides extending beyond the central region (32), - a trench (5) extends on each side along the resonator axis (3) and the trenches (5) laterally expose the current aperture layer (3) and sever the entire semiconductor layer sequence (2) down to a substrate (6), and - the trenches (5) are designed to suppress parasitic modes, so that the trenches (5) each have a cross-section with two side surfaces running obliquely to a growth direction (G) of the semiconductor layer sequence (2). [2] Semiconductor laser (1) according to claim 1, in which the current diaphragm layer (3) is located between the or one of the waveguide layers (22) and the associated cladding layer (23), wherein a distance between the current aperture layer (3) and the active zone (21) is at least 0.5 µm. [3] Semiconductor laser (1) according to one of the preceding claims, wherein the current aperture layer (3) has a thickness between 10 nm and 50 nm inclusive. [4] Semiconductor laser (1) according to one of the preceding claims, in which the current aperture layer (3) is formed from a III-V semiconductor material in the central region (32) and comprises at least one III-oxide in the edge regions (33), wherein the current aperture layer (3) has a different average thickness in the central region (32) than in the edge regions (33), so that a thickness difference between the central region (32) and the edge regions (33) is at most 2% of the average thickness of the central region (32). [5] Semiconductor laser (1) according to one of the preceding claims, in which the semiconductor layer sequence (2) is based on the material system AlInGaAs, wherein the current aperture layer (3) in the central region (32) is made of Al 1-z Ga z As is 0.01 ≤ z ≤ 0.

03. [6] Semiconductor laser (1) according to one of the preceding claims, in which layers (32, 33) of the semiconductor layer sequence (2) directly adjacent to the current aperture layer (3) are made of AlGaAs and an aluminum content in these layers (32, 33) is each between 10% and 50% inclusive. [7] Semiconductor laser (1) according to one of the preceding claims, in which facets (7) of the semiconductor layer sequence (2) for reflecting and / or coupling out a laser radiation (L) generated during operation in a radiation coupling-out region are free of electrically insulating regions of the current aperture layer (3), so that the edge regions (33) of the current aperture layer (3) have a constant width along the resonator axis (R). [8] Semiconductor laser (1) according to one of the preceding claims, in which a width of the edge regions (33) of the current aperture layer (3) is equal to the minimum width (M) with a tolerance of at most 0.5 µm, so that at least one of the electrical contact surfaces (4) is laterally flush with the semiconductor layer sequence (2). [9] Semiconductor laser (1) according to one of claims 1 to 7, wherein a width of the edge regions (33) of the current aperture layer (3) is greater than the minimum width (M), so that the semiconductor layer sequence (2) is wider than at least one of the electrical contact surfaces (4). [10] Semiconductor laser (1) according to one of the preceding claims, which comprises exactly one current aperture layer (3), wherein the current aperture layer (3) is located in a p-conductive region of the semiconductor layer sequence (2). [11] Semiconductor laser (1) according to one of claims 1 to 9, comprising two of the current aperture layers (3), wherein the active zone (21) is located between the current aperture layers (3). [12] Semiconductor laser (1) according to one of the preceding claims, whose emission wavelength is between 830 nm and 1.1 µm, wherein the semiconductor laser (1) is configured for multimode operation. [13] Manufacturing method for a semiconductor laser (1) according to one of the preceding claims, comprising the following steps: - epitaxial growth of the semiconductor layer sequence (2), - creating the trenches (5) on both sides along the resonator axis (3) so that the current aperture layer (3) is exposed laterally, - oxidizing the exposed current shield layer (3) starting from the trenches (5) so that the electrically insulating edge regions (33) are formed, - Applying the electrical contact surfaces (4), and - Separation to the semiconductor lasers (1). [14] Method according to the preceding claim, wherein the oxidation of the current aperture layer (3) is carried out wet-chemically at a temperature between 300 °C and 500 °C inclusive.

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