Edge-emitting semiconductor laser diode

Abstract

The invention relates to an edge-emitting semiconductor laser diode comprising: - a substrate (1) having a first main face (6) and a second main face (7) opposite the first main face (6), - an epitaxial semiconductor layer stack (2) on the first main face (6) of the substrate (1), wherein the epitaxial semiconductor layer stack (2) comprises an active layer (3) for generating electromagnetic radiation, - a matching layer (4) arranged on the second main face (7) of the substrate (1), and - an absorption layer (5) applied directly to the matching layer (4) and configured to at least partially absorb the electromagnetic radiation, wherein - the substrate (1) and the matching layer (4) are transparent to electromagnetic radiation generated during operation, and - the matching layer (4) is configured to increase the absorption of electromagnetic radiation in the absorption layer (5).

Description

[0001] Description

[0002] EDGE-EMITTING SEMI-DETAILED TERLASERDI ODE

[0003] An edge-emitting semiconductor laser diode is specified.

[0004] The aim is to provide an edge-emitting semiconductor laser diode with improved beam quality. This object is achieved by a subject matter having the features of the independent patent claim.

[0005] Advantageous embodiments and further developments of the edge-emitting semiconductor laser diode are specified in the dependent claims.

[0006] According to one embodiment, the edge-emitting semiconductor laser diode comprises a substrate with a first main surface and a second main surface opposite the first main surface. The substrate is, for example, a growth substrate or a carrier substrate. The substrate is designed, in particular, for mechanically stabilizing the edge-emitting semiconductor laser diode. The main surfaces preferably have a larger surface area than the side surfaces of the substrate.

[0007] The substrate comprises, for example, gallium nitride, sapphire, silicon, silicon carbide, or gallium arsenide or consists of one of these materials.

[0008] According to a further embodiment, the edge-emitting semiconductor laser diode has an epitaxial semiconductor layer stack on the first main surface of the substrate, wherein the epitaxial semiconductor layer stack comprises an active layer for generating electromagnetic radiation. For example, the epitaxial semiconductor layer stack is grown epitaxially on the first main surface of the substrate. A main extension plane of layers of the epitaxial semiconductor layer stack is preferably arranged parallel to the first main surface of the substrate.

[0009] The epitaxial semiconductor layer stack preferably comprises a II / IV compound semiconductor material or consists of a II / IV compound semiconductor material. A III / V compound semiconductor material comprises at least one element from the third main group, such as B, Al, Ga, In, and one element from the fifth main group, such as N, P, As. In particular, the term "III / V compound semiconductor material" encompasses the group of binary, ternary, or quaternary compounds that contain at least one element from the third main group and at least one element from the fifth main group, for example a nitride compound semiconductor material. Nitride compound semiconductor materials are compound semiconductor materials that contain nitrogen, such as the materials from the In system. x Al y Gai- x-y N with 0 < x < 1 , 0 < y < 1 and x+y < 1 .

[0010] The active layer preferably comprises a pn junction, a double heterostructure, a single quantum well, or particularly preferably a multiple quantum well structure (MQW) for generating radiation. The term "quantum well structure" does not specify the dimensionality of the quantization. It thus includes, among other things, quantum wells, quantum wires, and quantum dots, and any combination of these structures. The active layer is configured, for example, to generate electromagnetic radiation in a spectral range between infrared and ultraviolet light.

[0011] According to a further embodiment of the edge-emitting semiconductor laser diode, the substrate and the epitaxial semiconductor layer stack applied thereon have two opposing facets. The facets are, in particular, side surfaces of the substrate and the epitaxial semiconductor layer stack and are arranged, for example, perpendicular to or inclined at an angle to the first main surface of the substrate.

[0012] A highly reflective layer is preferably arranged on a facet, which is referred to below as the back facet, and is designed to reflect electromagnetic radiation generated during operation. For example, the highly reflective layer reflects at least 90%, preferably at least 99%, of the electromagnetic radiation incident thereon and generated during operation.

[0013] The facet opposite the rear facet is referred to below as the light output facet. The light output facet is designed to couple electromagnetic radiation generated during operation from the edge-emitting laser diode. An antireflective layer is preferably arranged on the light output facet, which has a lower reflectivity than the highly reflective layer on the rear facet. For example, the antireflective layer reflects between 10% and 80% of the electromagnetic radiation incident on it and generated during operation.

[0014] The back facet and the light-coupling facet, together with the layers applied thereto, form an optical resonator. The optical resonator can also comprise additional optical elements, such as external mirrors. Electromagnetic radiation generated in the active layer during operation forms a standing electromagnetic wave in the optical resonator.

[0015] The active layer, in conjunction with the optical resonator, is designed to generate electromagnetic laser radiation. Electromagnetic laser radiation is generated by stimulated emission and, in contrast to electromagnetic radiation generated by spontaneous emission, typically exhibits a very high coherence length, a very narrow spectral linewidth, and / or a high degree of polarization.

[0016] According to a further embodiment, the edge-emitting semiconductor laser diode has at least one matching layer arranged on the second main surface of the substrate. For example, the matching layer is applied directly to the second main surface of the substrate. The matching layer preferably comprises a dielectric material or a semiconductor material, or consists of one of these materials. The edge-emitting laser diode can also have multiple matching layers.

[0017] According to a further embodiment, the edge-emitting semiconductor laser diode has an absorption layer which is applied directly to the matching layer and is configured to at least partially absorb electromagnetic radiation generated during operation. The absorption layer is preferably applied to a side of the matching layer facing away from the substrate and covers the matching layer completely or partially. The absorption layer is configured in particular to at least partially absorb electromagnetic laser modes propagating in the substrate. For example, the absorption layer has an absorption coefficient of at least 100 cur 1 , preferably at least 1000 cur 1 , for electromagnetic radiation generated during operation.

[0018] According to a further embodiment of the edge-emitting semiconductor laser diode, the substrate and the matching layer are transparent to electromagnetic radiation generated during operation. In particular, a band gap of the substrate and a band gap of the matching layer are larger than a band gap of the active layer of the epitaxial semiconductor layer stack. For example, the substrate and the matching layer have transmittances for electromagnetic radiation generated during operation of at least 5%, preferably of at least 10%, and particularly preferably of at least 50%.

[0019] According to a further embodiment of the edge-emitting semiconductor laser diode, the matching layer is configured to increase the absorption of electromagnetic radiation in the absorption layer. In particular, the matching layer is configured to adjust a phase and a position of intensity maxima of the laser modes propagating in the substrate such that these laser modes experience strong attenuation by the absorption layer. For example, the attenuation of the laser modes propagating in the substrate in an edge-emitting semiconductor laser diode with the matching layer is at least one order of magnitude greater, preferably at least two orders of magnitude greater, than in an otherwise structurally identical edge-emitting semiconductor laser diode without the matching layer.

[0020] According to a preferred embodiment, the edge-emitting semiconductor laser diode has at least the following features:

[0021] - a substrate having a first main surface and a second main surface opposite the first main surface,

[0022] - an epitaxial semiconductor layer stack on the first main surface of the substrate, wherein the epitaxial semiconductor layer stack comprises an active layer for generating electromagnetic radiation,

[0023] - a matching layer arranged on the second main surface of the substrate, and

[0024] - an absorption layer which is applied directly to the matching layer and is designed to at least partially absorb the electromagnetic radiation, wherein

[0025] - the substrate and the matching layer are transparent to electromagnetic radiation generated during operation, and

[0026] - the matching layer is designed to increase the absorption of electromagnetic radiation in the absorption layer.

[0027] In edge-emitting semiconductor laser diodes, layers of the epitaxial semiconductor layer stack are arranged in particular such that the electromagnetic radiation generated during operation is guided therein and coupled out at the light output facet. For example, the active layer is arranged between two cladding layers designed to guide the electromagnetic radiation laterally. Lateral here and in the following refers to a direction parallel to the first main surface of the substrate.

[0028] Due to scattering from roughness and / or defects and / or due to cladding layers that are too thin, a portion of the electromagnetic radiation generated during operation can be coupled from the semiconductor layer stack into the substrate. Electromagnetic laser modes therefore propagate in a transparent substrate, and the substrate can act as a waveguide for these laser modes. These electromagnetic laser modes propagating in the substrate, which are also referred to below as substrate modes, can also be coupled out at the light output facet of the edge-emitting semiconductor laser diode. The substrate modes lead, for example, to additional intensity peaks in a far field of the laser radiation generated during operation. In particular, the substrate modes impair beam quality and thus imaging and / or image quality of a laser beam coupled out from the edge-emitting semiconductor laser diode.

[0029] The edge-emitting semiconductor laser diode described here is based on the idea of ​​suppressing these substrate modes by applying suitable layers on a main surface of the substrate opposite the epitaxial semiconductor layer stack.

[0030] For example, substrate modes are at least partially absorbed by the absorption layer. However, strongly absorbing absorption layers, such as metallic absorption layers, can exhibit high reflectivity. As a result, substrate modes are particularly reflected at the interface to the absorption layer, which can limit and / or hinder the suppression of substrate modes by the absorption layer.

[0031] The matching layer sets the phase and position of intensity maxima of the substrate modes in particular such that the substrate modes experience strong attenuation by the absorption layer. For example, the attenuation of the substrate modes in a semiconductor laser diode with the matching layer is two orders of magnitude greater than in an otherwise identical semiconductor laser diode without the matching layer. The matching layer is preferably transparent to electromagnetic radiation generated during operation and in particular has a higher refractive index than the substrate. Substrate modes that couple into the matching layer and are reflected at the absorption layer are thus totally reflected, for example at an interface between the matching layer and the substrate, and deflected back in the direction of the absorption layer. This can in particular increase the absorption of electromagnetic radiation in the absorption layer.

[0032] The matching layer, in combination with the absorption layer, enables simple and cost-effective suppression of interfering substrate modes. This increases, in particular, the beam quality of the edge-emitting laser diode, thereby achieving improved imaging and image quality.

[0033] According to a further embodiment of the edge-emitting semiconductor laser diode, the substrate is a growth substrate for the epitaxial semiconductor layer stack. In particular, the epitaxial semiconductor layer stack is grown epitaxially on the substrate.

[0034] According to a further embodiment of the edge-emitting semiconductor laser diode, the matching layer reduces a distance between the absorption layer and an intensity maximum of electromagnetic laser modes propagating in the substrate. In other words, the matching layer is designed to bring the intensity maxima of a plurality of electromagnetic laser modes propagating in the substrate closer to the absorption layer. By reducing the distance between the intensity maxima and the absorption layer, the absorption of the laser modes propagating in the substrate is advantageously increased.

[0035] Preferably, this effect of the matching layer is not limited to individual, selected substrate modes. Rather, the matching layer affects a large portion of the electromagnetic laser modes propagating in the substrate.

[0036] According to a further embodiment of the edge-emitting semiconductor laser diode, the matching layer reduces reflection of electromagnetic laser modes propagating in the substrate at the absorption layer. This increases, in particular, absorption of electromagnetic laser modes propagating in the substrate by the absorption layer. For example, a thickness of the absorption layer is set such that a portion of a plurality of substrate modes reflected at the interface between the substrate and the matching layer interferes as destructively as possible with a portion of these substrate modes reflected at an interface between the matching layer and the absorption layer. According to a further embodiment of the edge-emitting semiconductor laser diode, a refractive index of the matching layer for electromagnetic radiation generated during operation is greater than a refractive index of the substrate for electromagnetic radiation generated during operation.Thus, electromagnetic laser radiation propagating in the substrate can be coupled into the matching layer, while electromagnetic laser radiation propagating in the matching layer can be totally reflected at the interface to the substrate. This increases, in particular, the attenuation of substrate modes by the absorption layer.

[0037] For example, the refractive index of the matching layer is at least 0.01 and at most 5 greater than the refractive index of the substrate. Preferably, the refractive index of the matching layer is at least 0.1 and at most 1.5 greater than the refractive index of the substrate. Particularly preferably, the refractive index of the matching layer is at least 0.15 and at most 0.7 greater than the refractive index of the substrate.

[0038] According to a further embodiment of the edge-emitting semiconductor laser diode, an extinction coefficient of the matching layer for electromagnetic radiation generated during operation is at most 2. Preferably, the extinction coefficient of the matching layer is at most 0.7 and particularly preferably at most 0.1. The lower the extinction coefficient of the matching layer, the more transparent the matching layer is for electromagnetic radiation generated during operation.

[0039] According to a further embodiment of the edge-emitting

[0040] For a semiconductor laser diode, the thickness of the matching layer is proportional to the wavelength of electromagnetic radiation generated during operation and inversely proportional to the refractive index of the matching layer for electromagnetic radiation generated during operation. Here and in the following, the thickness of a layer refers to a spatial extent in a direction perpendicular to the second main surface of the substrate.

[0041] According to a further embodiment of the edge-emitting semiconductor laser diode, a thickness of the matching layer D = D o + m * Ad with a tolerance of ± 30 nanometers . Where — and m is a J substrate integer greater than or equal to zero , where X is the wavelength of electromagnetic radiation generated during operation, n is the refractive index of the matching layer for electromagnetic radiation generated during operation and n Substrat denotes the refractive index of the substrate for electromagnetic radiation generated during operation. Preferably, m is zero and thus D = D o . The formula given above for the thickness of the matching layer only applies to matching layers with a refractive index greater than approximately 2.5 and greater than the refractive index of the substrate .

[0042] By selecting the thickness of the matching layer according to the above formula, the attenuation of electromagnetic laser modes propagating in the substrate can be advantageously increased. For example, the strength of the substrate modes is reduced by three to four orders of magnitude due to the matching layer with the thickness specified above, compared to a corresponding edge-emitting semiconductor laser diode without a matching layer. According to a further embodiment of the edge-emitting semiconductor laser diode, the matching layer has a lateral structuring, so that only a part of the second main surface of the substrate is covered by the matching layer and / or the matching layer has at least two separate segments and / or the matching layer has at least one recess.In the event that the matching layer is electrically insulating , a lateral structuring of the matching layer is advantageous , in particular for electrically contacting the epitaxial semiconductor layer stack via the second main surface of the substrate .

[0043] According to a further embodiment of the edge-emitting semiconductor laser diode, the matching layer comprises titanium oxide, non-stoichiometric silicon oxide, non-stoichiometric silicon nitride, silicon carbide or gallium phosphide, or consists of one of these materials.

[0044] According to a further embodiment, the edge-emitting semiconductor laser diode has at least two matching layers arranged between the second main surface of the substrate and the absorption layer. The matching layers can comprise different materials or different material compositions. This can improve the attenuation and thus the suppression of electromagnetic laser modes propagating in the substrate.

[0045] According to a further embodiment of the edge-emitting semiconductor laser diode, the matching layer is electrically conductive. Thus, the epitaxial semiconductor layer stack can be electrically contacted, in particular, via an electrically conductive absorption layer, the electrically conductive matching layer, and an electrically conductive substrate.

[0046] According to a further embodiment of the edge-emitting semiconductor laser diode, the absorption layer is configured as a contact layer for electrically contacting the epitaxial semiconductor layer stack. In particular, the absorption layer is electrically conductive. This allows for the elimination of process steps in the manufacture of the edge-emitting semiconductor laser diode, thus reducing costs.

[0047] According to a further embodiment of the edge-emitting semiconductor laser diode, the absorption layer comprises a metal, a semiconductor material or a non-stoichiometric dielectric or consists of one of these materials.

[0048] According to a further embodiment, the edge-emitting semiconductor laser diode additionally has a light-blocking layer arranged on a partial region of the light-output facet of the semiconductor laser diode and configured to at least partially absorb and / or reflect electromagnetic laser modes propagating in the substrate. The light-blocking layer is preferably arranged on a partial region of the light-output facet that encompasses the substrate. In particular, the light-output facet remains free of the light-blocking layer in the region of the active layer.

[0049] The light-blocking layer may have or consist of multiple sublayers. For example, the transmission of the light-blocking layer for electromagnetic radiation generated during operation is at most 20%. The light-blocking layer comprises, in particular, an oxide, an oxynitride, or a metal, for example, aluminum oxide, silicon oxynitride, titanium, platinum, or chromium, or consists of one of these materials.

[0050] According to a further embodiment, the edge-emitting semiconductor laser diode has a contact layer that is applied to the absorption layer and is configured for electrically contacting the epitaxial semiconductor layer stack. Preferably, the contact layer is arranged directly on the absorption layer. The contact layer comprises, for example, a metal or is formed from a metal. The contact layer is configured for electrically contacting the epitaxial semiconductor layer stack via the second main surface of the substrate.

[0051] Alternatively or additionally, the contact layer can also be arranged on the first main surface of the substrate. A further contact layer is arranged, for example, on a main surface of the epitaxial semiconductor layer stack facing away from the substrate.

[0052] According to a further embodiment of the edge-emitting semiconductor laser diode, the active layer has at least two emission regions arranged laterally next to one another, which are designed to generate electromagnetic radiation in different wavelength ranges. For example, the emission regions arranged next to one another have different material compositions and thus different band gaps. The emission regions can preferably be electrically contacted independently of one another and can thus be operated and / or controlled independently of one another. The emission regions of the active layer arranged next to one another can also generate electromagnetic radiation in the same wavelength range. For example, the edge-emitting semiconductor laser diode is designed as a laser bar.

[0053] According to a further embodiment of the edge-emitting semiconductor laser diode, the matching layer has at least two subregions arranged laterally next to one another, wherein one subregion in each case is arranged below an emission region in a direction perpendicular to the first main surface of the substrate. In particular, each emission region of the active layer has an associated subregion of the matching layer on the opposite main surface of the substrate. The subregions of the matching layer can be connected to one another or spatially separated from one another.

[0054] According to a further embodiment of the edge-emitting semiconductor laser diode, the subregions of the matching layer comprise different materials and / or different thicknesses. If the active layer comprises multiple emission regions configured to generate electromagnetic radiation in different wavelength ranges, the thickness of the matching layer in the different subregions can, for example, be selected to match an emitter wavelength of the individual emission regions.

[0055] Further advantageous embodiments and developments of the edge-emitting semiconductor laser diode will become apparent from the embodiments described below in conjunction with the figures.

[0056] Figures 1 and 2 show profiles of electromagnetic laser radiation in the far field of an edge-emitting semiconductor laser diode.

[0057] Figures 3, 4 and 5 show various schematic representations of an edge-emitting semiconductor laser diode according to an embodiment.

[0058] Figures 6 and 7 show schematic representations of a mode strength of substrate modes as a function of a thickness of the matching layer.

[0059] Figure 8 shows a schematic representation of a thickness of the matching layer as a function of a refractive index of the matching layer.

[0060] Figure 9 shows a schematic representation of a mode strength of substrate modes as a function of a refractive index of the matching layer.

[0061] Figure 10 shows a schematic representation of a mode strength of substrate modes as a function of an extinction coefficient of the matching layer.

[0062] Figures 11 to 15 show schematic sectional views of edge-emitting semiconductor laser diodes according to further embodiments.

[0063] Figures 16 to 23 show schematic plan views of the second main surface of the substrate of edge-emitting semiconductor laser diodes according to various

[0064] From examples.

[0065] Figures 24 to 26 show schematic sectional views of edge-emitting semiconductor laser diodes according to further embodiments.

[0066] Figure 27 shows a schematic representation of the intensity of substrate modes according to an embodiment.

[0067] Identical, similar, or functionally identical elements are provided with the same reference symbol in the figures. The figures and the relative sizes of the elements depicted in the figures are not to be considered to scale. Rather, individual elements, particularly layer thicknesses, may be exaggerated for clarity and / or clarity.

[0068] Figure 1 shows a cross-section of the laser beam coupled out by the edge-emitting laser diode. The electromagnetic laser radiation has, in particular, a Gaussian mode profile 20 with different mode widths in two mutually orthogonal directions. The area marked with an ellipse shows additional structures in the coupled-out laser beam, which are caused by electromagnetic laser modes 9 propagating in the substrate 1. These substrate modes 9 are at least partially coupled out by the edge-emitting semiconductor laser diode, impair the beam quality and lead, for example, to poorer imaging quality.

[0069] Figure 2 shows a mode profile 20 of electromagnetic laser radiation in the far field of an edge-emitting semiconductor laser diode, wherein the intensity I of the electromagnetic laser radiation is shown as a function of an emission angle α. The electromagnetic laser radiation has, in particular, a Gaussian mode profile 20. Furthermore, the mode profile 20 shows additional intensity peaks 24 of the electromagnetic laser radiation, which are caused by electromagnetic laser modes 9 propagating in the substrate 1 and coupled out by the edge-emitting semiconductor laser diode. The edge-emitting semiconductor laser diode described here is based on the idea of ​​largely suppressing these additional intensity peaks 24.

[0070] The edge-emitting semiconductor laser diode according to the exemplary embodiment of Figure 3 has a substrate 1 with an epitaxial semiconductor layer stack 2 applied thereon. The epitaxial semiconductor layer stack 2 is applied to a first main surface 6 of the substrate 1 and comprises, for example, a nitride compound semiconductor material. The epitaxial semiconductor layer stack 2 comprises an active layer 3 for generating electromagnetic radiation. Furthermore, the epitaxial semiconductor layer stack 2 has cladding layers 10 for guiding the electromagnetic laser radiation generated during operation in the active layer 3, wherein the active layer 3 is arranged between two cladding layers 10.

[0071] The substrate 1 is in particular a growth substrate on which the epitaxial semiconductor layer stack 2 has been grown epitaxially. For example, the substrate 1 comprises gallium nitride or silicon carbide or consists of one of these materials. The substrate 1 is transparent to electromagnetic laser radiation generated during operation. In particular, the substrate 1 has a larger band gap than the active layer 3 of the epitaxial semiconductor layer stack 2. Electromagnetic laser radiation generated during operation can thus at least partially couple from the active layer 3 into the transparent substrate 1 and propagate in the substrate 1 as an electromagnetic laser mode 9.

[0072] A matching layer 4 is applied directly to the second main surface 7 of the substrate 1. The matching layer 4 comprises a dielectric material or a semiconductor material that is transparent to electromagnetic radiation generated during operation. For example, the matching layer 4 comprises or consists of gallium phosphide.

[0073] In particular, a refractive index n of the matching layer 4 for electromagnetic radiation generated during operation is greater than a refractive index of the substrate 1. For example, the refractive index n of the matching layer 4 is at least 0.15 and at most 0.7 greater than the refractive index of the substrate 1. Furthermore, the extinction coefficient k of the matching layer is preferably at most 0.1.

[0074] An absorption layer 5 is applied directly to the main surface of the matching layer 4 opposite the substrate 1. The absorption layer 5 has, in particular, a high absorption coefficient for electromagnetic radiation generated during operation and is formed, for example, from a metal.

[0075] A thickness D of the matching layer 4 is selected such that substrate modes 9 are absorbed as strongly as possible by the absorption layer 5 and thus attenuated. For example, the matching layer 4 reduces reflection of substrate modes 9 at the absorption layer 5. The thickness D of the matching layer 4 is, in particular, proportional to the wavelength of electromagnetic radiation generated during operation and inversely proportional to a refractive index n of the matching layer.

[0076] A contact layer 19 for electrically contacting the active layer 3 is arranged on a main surface of the epitaxial semiconductor layer stack 2 opposite the substrate 1. Furthermore, the absorption layer 5 is designed as a further contact layer for electrically contacting the active layer 3, the substrate 1 being electrically conductive. For example, the substrate comprises a doped semiconductor material. The matching layer 4 arranged between the substrate 1 and the absorption layer 5 is either electrically conductive or has a lateral structuring 11. Examples of lateral structurings 11 of the matching layer 4 are shown in Figures 16 to 23. As a result of the lateral structuring 11 of the matching layer 4, the edge-emitting semiconductor laser diode has, in particular, a direct, electrically conductive connection between the absorption layer 5 and the substrate 1.

[0077] Opposite side surfaces of the semiconductor laser diode are designed as a light output facet 15 and a rear facet 18, which together form an optical resonator of the edge-emitting semiconductor laser diode. The optical resonator, in conjunction with the active layer 3, is designed to generate electromagnetic laser radiation during operation. The electromagnetic laser radiation is output via the light output facet 15 and emitted by the edge-emitting semiconductor laser diode at the emission angle α. The emission angle α refers to an angle between a surface normal of the light output facet 15 and an emission direction of the electromagnetic laser radiation generated during operation.

[0078] Figure 4 shows a schematic perspective view of the edge-emitting semiconductor laser diode according to the exemplary embodiment of Figure 3. The epitaxial semiconductor layer stack 2 has, in particular, a ridge waveguide 22 for guiding electromagnetic radiation generated during operation. The ridge waveguide 22 extends in the lateral direction between the light output facet 15 and the opposite rear facet 18. The contact layer 19 for electrically contacting the active layer 3 completely covers the ridge waveguide 22.

[0079] The matching layer 4 only partially covers the second main surface 7 of the substrate 1. In particular, a region of the second main surface 7 is covered by the matching layer 4 in the vertical direction above the ridge waveguide 22. The matching layer 4 covers a region of the second main surface 7 which extends beyond the ridge waveguide 22 in the lateral direction perpendicular to a main extension direction of the ridge waveguide 22, preferably by at least 30 micrometers, particularly preferably by at least 60 micrometers. Regions of the second main surface 7 which are not covered by the matching layer 4 are covered by the absorption layer 5, which extends over the entire second main surface 7. The absorption layer 5 is therefore in direct electrical contact with the electrically conductive substrate 1 and is designed to electrically contact the semiconductor layer stack 2.Figure 5 shows a schematic sectional view of the edge-emitting semiconductor laser diode according to the embodiment of Figure 3 in a plan view of the light output facet 15. In particular, the matching layer 4 does not completely cover the second main surface 7 of the substrate 1, but protrudes in the lateral direction on both sides by at least 30 micrometers beyond the ridge waveguide 22.

[0080] Figure 6 schematically shows a relationship between a thickness D of the matching layer 4 and a mode strength S of the substrate modes 9. The mode strength S indicates, in particular, a relative intensity of the substrate modes 9 coupled out by the semiconductor laser diode. A mode strength S with the value S=1 corresponds to a semiconductor laser diode without an absorption layer 5 and is marked with an asterisk in Figure 4. In contrast, a semiconductor laser diode of the same construction with an additional absorption layer 5 but without a matching layer 4 has a lower mode strength S, which is marked with a square in Figure 4.

[0081] Furthermore, Figure 4 shows the mode strength S of substrate modes 9 of a semiconductor laser diode with an absorption layer 5 and a matching layer 4 as a function of the thickness D of the matching layer 4. In particular, Figure 4 shows that the mode strength S of the substrate modes 9 can be reduced by, for example, two orders of magnitude by a suitable choice of the thickness D of the matching layer 4.

[0082] Figure 7 shows the results of a numerical simulation of the mode strength S of substrate modes 9 as a function of the thickness D of the matching layer 4 . The mode strength S exhibits several approximately periodically occurring minima 21 . The first minimum 21 occurs at a thickness D of the matching layer 4 denoted by Do . Further minima 21 occur approximately at thicknesses D = D o + m * Ad of the matching layer 4 , where Ad =

[0083] — , = and m is an integer greater than or equal to zero .

[0084] 2 n2 ~ n Substrat

[0085] Here, n and n Su bstrat refractive indices of the matching layer 4 and the substrate 1 for electromagnetic radiation generated during operation.

[0086] Figure 8 shows the thickness Do at which the first minimum 21 of the

[0087] Mode strength S in Figure 5, as a function of the

[0088] Refractive index n of the matching layer 4 . The thickness Do can be

[0089] _ x _ approximately by the function D o

[0090] 450*(0.00192*n 2 +0.01873 *n-0.05235), where X is the wavelength of electromagnetic radiation generated during operation and n is the refractive index of the

[0091] Matching layer 4 .

[0092] Figure 9 shows numerical results for the mode strength S of substrate modes 9 as a function of the refractive index n of the matching layer 4. The thickness D of the matching layer 4 and the optical properties of the absorption layer 5 are fixed. In particular, Figure 7 shows that the mode strength S of the substrate modes 9 exhibits a pronounced minimum 21 at a specific value of the refractive index n of the matching layer 4. This value depends, among other things, on the optical properties of the absorption layer 5, in particular on the complex refractive index of the absorption layer 5.

[0093] Figure 10 shows a mode strength S of substrate modes 9 as a function of an extinction coefficient k of the matching layer 4. The thickness D and the refractive index n of the matching layer 4, as well as the optical properties of the absorption layer 5, are fixed. In particular, Figure 8 shows that the smallest possible extinction coefficient k of the matching layer 4 results in a particularly low mode strength S of the substrate modes 9. In other words, the smallest possible extinction coefficient k of the matching layer 4 leads to an advantageously large attenuation of the substrate modes 9.

[0094] In contrast to the semiconductor laser diode in Figure 3, the edge-emitting semiconductor laser diode according to the embodiment of Figure 11 has a plurality of matching layers 4 arranged between the substrate 1 and the absorption layer 5. The various matching layers 4 have, for example, different materials and thus different optical properties, in particular different refractive indices n. This allows the attenuation of the substrate modes 9 to be adjusted more finely and thus improved.

[0095] 12 additionally has a light blocking layer 14 compared to the semiconductor laser diode in FIG. 3. The light blocking layer 14 partially covers the light output facet 15, in particular in the region of the substrate 1. The light blocking layer 14 is designed for the at least partial absorption and / or reflection of substrate modes 9. This at least partially reduces or prevents the output of substrate modes 9 from the semiconductor laser diode. In conjunction with the matching layer 4 and the absorption layer 5, substrate modes 9 in the far field of the laser radiation output from the semiconductor laser diode can thereby be suppressed even more strongly. In contrast to the edge-emitting semiconductor laser diode in FIG. 5, the embodiment in FIG. 13 has a matching layer 4 which completely covers the second main surface 7 of the substrate 1.The matching layer 4 is electrically conductive to ensure electrical contact between the absorption layer 5 and the epitaxial semiconductor layer stack 2 via the electrically conductive substrate 1.

[0096] In contrast to the edge-emitting semiconductor laser diode in Figure 13, in the exemplary embodiment of the edge-emitting semiconductor laser diode in Figure 14, the absorption layer 5 is not configured as a contact layer. Thus, no electrically conductive matching layer 4 and no electrically conductive substrate 1 are necessary for electrically contacting the epitaxial semiconductor layer stack 2. Instead, the contact layers 19 for electrically contacting the epitaxial semiconductor layer stack 2 are arranged parallel to the ridge waveguide 22 and laterally spaced from the epitaxial semiconductor layer stack 2 on the first main surface 6 of the substrate 1, as well as on the main surface of the epitaxial semiconductor layer stack 2 facing away from the substrate 1.

[0097] In the edge-emitting semiconductor laser diode according to the embodiment in Figure 15, an area in which the absorption layer 5 is in direct contact with the second main surface 7 of the substrate 1 is larger than in the edge-emitting semiconductor laser diode in Figure 12. As a result, in the case of a non-electrically conductive matching layer 4, an electrical contact between the

[0098] absorption layer 5 and the substrate 1 can be improved.

[0099] Figure 16 shows a plan view of the second main surface 7 of the substrate 1 of an edge-emitting semiconductor laser diode. The second main surface 7 is partially free of the matching layer 4, while the absorption layer 5 extends over the entire second main surface 7. In particular, a region at the edge of the second main surface 7, which extends between the light output facet 15 and the rear facet 18, is free of the matching layer 4.

[0100] In the edge-emitting semiconductor laser diode in Figure 17, in contrast to Figure 16, two regions at opposite edges of the second main surface 7 are free of the matching layer 4.

[0101] In Figure 18, in contrast to Figure 17, the absorption layer 5 does not completely cover the substrate 1. However, the matching layer 4 is completely covered by the absorption layer 5.

[0102] In Figure 19, the matching layer 4 and the absorption layer 5 are laterally spaced from the light output facet 15 and the back facet 18, in contrast to Figure 18.

[0103] In contrast to the edge-emitting semiconductor diode in Figure 19, the matching layer 4 in Figure 20 has an additional lateral structuring 11. In particular, the matching layer 4 has a plurality of separate segments 12 arranged along a direction between the light output facet 15 and the rear facet 18.

[0104] In the edge-emitting semiconductor laser diode in Figure 21, in comparison to Figure 17, only a partial area of ​​the second main surface 7 at the light output facet 18 is covered by the matching layer 4.

[0105] In contrast to the edge-emitting semiconductor laser diode of Figure 20, the edge-emitting semiconductor laser diode in Figure 22 has a lateral structuring 11 of the matching layer 4 in the form of a plurality of recesses 13.

[0106] The edge-emitting semiconductor laser diode in Figure 23 has an absorption layer 5 comprising two separate segments 12. The two segments 12 are arranged near the light-output facet 15 and the rear-side facet, while the matching layer 4 covers a region of the second main surface 7 adjacent to the light-output facet 15.

[0107] Figure 24 shows a plan view of the light output facet 15 of an edge-emitting semiconductor laser diode. The epitaxial semiconductor layer stack 2 has three emission regions 16 that are laterally spaced apart from one another. The three emission regions 16 are electrically contacted independently of one another by separate contact layers 19 and can thus be controlled and / or operated independently of one another. For each emission region 16, an associated partial region 17 of the matching layer 4 and the absorption layer 5 is applied to the second main surface 7 of the substrate 1 and is arranged directly opposite the respective emission region 16. The partial regions 17 of the matching layer 4 in the edge-emitting semiconductor laser diode in Figure 25 have different properties in contrast to Figure 24. For example, the matching layer 4 has different thicknesses D and / or different material compositions in the partial regions 17.Thus, the matching layer 4 in the partial regions 17 can be adapted, for example, to different emission wavelengths of the different emission regions 16.

[0108] Figure 26 shows an edge-emitting semiconductor laser diode which, in contrast to Figure 24, has a continuous matching layer 4. In particular, the matching layer 4 is not divided into separate subregions 17. Thus, all emission regions 16 of the semiconductor layer stack 2 share a common matching layer 4.

[0109] Figure 27 shows a schematic representation of an intensity I of substrate modes 9 in a direction R perpendicular to the second main surface 7 of the substrate 1. The substrate modes 9 are represented as standing electromagnetic waves in this direction R. At the interface between the matching layer 4 and the metallic absorption layer 5, the substrate modes 9 have in particular a node at which the intensity I of the substrate modes 9 disappears. The matching layer 4 moves intensity maxima 23 of the substrate modes 9 closer to the absorption layer 5. Thus, attenuation of the substrate modes 9 by the absorption layer 5 is advantageously increased. This patent application claims priority from German patent application DE 102022104418.1, the disclosure of which is hereby incorporated by reference. The invention is not limited to the description based on the exemplary embodiments.Rather, the invention encompasses any new feature and any combination of features, which in particular includes any combination of features in the patent claims, even if this feature or combination itself is not explicitly stated in the patent claims or embodiments.

[0110] Reference symbol list

[0111] 1 substrate

[0112] 2 epitaxial semiconductor layer stack

[0113] 3 active layer

[0114] 4 Adaptation layer

[0115] 5 Absorption layer

[0116] 6 first main area

[0117] 7 second main area

[0118] 8 Distance

[0119] 9 Substrate mode

[0120] 10 Sheath layer

[0121] 11 Structuring

[0122] 12 segments

[0123] 13 Recess

[0124] 14 Light blocking layer

[0125] 15 light output facet

[0126] 16 Emission range

[0127] 17 sub-area

[0128] 18 back facet

[0129] 19 Contact layer

[0130] 20 Fashion Profile

[0131] 21 minimum

[0132] 22 ridge waveguides

[0133] 23 Intensity maximum

[0134] 24 intensity peak

[0135] I Intensity

[0136] S Mode strength n Refractive index k Extinction coefficient

[0137] D Thickness a Beam angle

[0138] R direction

Claims

Patent claims 1. Edge-emitting semiconductor laser diode, comprising: - a substrate (1) with a first main surface (6) and a second main surface (7) opposite the first main surface (6) , - an epitaxial semiconductor layer stack (2) on the first main surface (6) of the substrate (1) , wherein the epitaxial semiconductor layer stack (2) comprises an active layer (3) for generating electromagnetic radiation, - at least one adaptation layer (4) which is arranged on the second main surface (7) of the substrate (1), and - an absorption layer (5) which is applied directly to the matching layer (4) and is designed to absorb at least part of the electromagnetic radiation, wherein - the substrate (1) and the matching layer (4) are transparent to electromagnetic radiation generated during operation, and - the matching layer (4) is designed to reduce the absorption of electromagnetic radiation in the absorption layer (5) to increase.

2. Edge-emitting semiconductor laser diode according to the preceding claim, wherein the substrate (1) is a growth substrate for the epitaxial semiconductor layer stack (2).

3. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the matching layer (4) provides a distance (8) between the absorption layer (5) and an intensity maximum (23) of reduced in the substrate (1) propagating electromagnetic laser modes (9).

4. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the matching layer (4) provides a reflection from the substrate (1) propagating electromagnetic laser modes (9) at the absorption layer (5) is reduced.

5. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein a refractive index (n) of the matching layer (4) for electromagnetic radiation generated in operation is greater than a refractive index of the substrate (1) for electromagnetic radiation generated in operation.

6. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein an extinction coefficient (k) of the matching layer (4) for electromagnetic radiation generated during operation is at most 2.

7. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein a thickness (D) of the matching layer (4) is proportional to a wavelength of electromagnetic radiation generated in operation and inversely proportional to a refractive index (n) of the matching layer (4) for electromagnetic radiation generated in operation.

8. Edge-emitting semiconductor laser diode according to any one of the preceding claims, where a thickness (D) of the adaptation layer (4) D = D o + m * Ad with a tolerance of ±30 nanometers, where , m is an integer J substrate greater than or equal to zero, X a wavelength of electromagnetic radiation generated during operation, n a refractive index of the matching layer (4) for electromagnetic radiation generated during operation and n Su bstrat denotes a refractive index of the substrate (1) for electromagnetic radiation generated during operation.

9. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the matching layer (4) has a lateral structuring (11) such that only a part of the second main surface (7) of the substrate is covered by the matching layer and / or the matching layer (4) has at least two separate segments (12) and / or the matching layer (4) has at least one recess (13).

10. Edge-emitting semiconductor laser diode according to any of the preceding claims, wherein the matching layer (4) comprises titanium oxide, non-stoichiometric silicon oxide, non-stoichiometric silicon nitride, silicon carbide, or gallium phosphide.

11. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the matching layer (4) is electrically conductive.

12. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the absorption layer (5) is configured as a contact layer (19) for electrical contacting the epitaxial semiconductor layer stack (2).

13. Edge-emitting semiconductor laser diode according to any of the preceding claims, wherein the absorption layer (5) comprises a metal, a semiconductor material, or a non-stoichiometric dielectric.

14. Edge-emitting semiconductor laser diode according to one of the preceding claims, further comprising a light-blocking layer (14) which is arranged on a partial region of a light-exiting facet (15) of the semiconductor laser diode and is configured to at least partially absorb and / or reflect electromagnetic laser modes (9) propagating in the substrate (1).

15. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the active layer (3) has at least two laterally adjacent emission regions (16) which are configured to generate electromagnetic radiation in different wavelength ranges.

16. Edge-emitting semiconductor laser diode according to the previous claim, wherein the matching layer (4) has at least two laterally adjacent sub-regions (17) and wherein each sub-region (17) is arranged in a direction perpendicular to the first main surface (6) of the substrate (1) under an emission region (16).

17. Edge-emitting semiconductor laser diode according to the previous claim, wherein the sub-regions (17) of the matching layer (4) have different materials and / or different thicknesses (D).

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