Edge-emitting semiconductor laser diode

Abstract

1. An edge-emitting semiconductor laser diode comprising: a substrate (1) having a first main surface (6) and a second main surface (7) opposite to the first main surface (6); an epitaxial semiconductor layer stack (2) comprising an active layer (3) for generating electromagnetic radiation and provided on the first main surface (6) of the substrate (1); at least one matching layer (4) arranged on the second main surface (7) of the substrate (1); and an absorption layer (5) arranged directly on the matching layer (4) and configured to at least partially absorb 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 absorption of the electromagnetic radiation in the absorption layer (5).

Description

[Technical field]

[0001] An edge-emitting semiconductor laser diode is identified.

[0002] To identify an edge-emitting semiconductor laser diode with improved beam quality, the object is solved by a device having the features of the independent patent claims.

[0003] Advantageous embodiments and further developments of the edge-emitting semiconductor laser diode are specified in the dependent claims.

[0004] According to one embodiment, the edge-emitting semiconductor laser diode includes a substrate having a first major surface and a second major surface opposite the first major surface. The substrate is, for example, a growth substrate or a carrier substrate. In particular, the substrate is configured to mechanically stabilize the edge-emitting semiconductor laser diode. The major surface preferably has a larger surface area than the side surfaces of the substrate.

[0005] The substrate may, for example, comprise or consist of gallium nitride, sapphire, silicon, silicon carbide, or gallium arsenide.

[0006] According to another embodiment, the edge-emitting semiconductor laser diode comprises an epitaxial semiconductor layer stack on a first main surface of a substrate, the epitaxial semiconductor layer stack comprising an active layer for generating electromagnetic radiation. For example, the epitaxial semiconductor layer stack is epitaxially grown on the first main surface of the substrate. The main extension planes of the layers of the epitaxial semiconductor layer stack are preferably arranged parallel to the first main surface of the substrate.

[0007] The epitaxial semiconductor layer stack preferably comprises or consists of III-V compound semiconductor materials. III-V compound semiconductor materials contain 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 materials" includes the group of binary, ternary or quaternary compounds containing at least one element from the third main group and at least one element from the fifth main group, such as nitride compound semiconductor materials. Nitride-based compound semiconductor materials are compound semiconductor materials containing nitrogen, such as In, with 0≦x≦1, 0≦y≦1, x+y≦1. x Al y Ga 1-x-y Examples of such materials include N-based materials.

[0008] The active layer preferably consists of 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 indicate the dimensionality of the quantization. Thus, quantum wells, quantum wires and quantum dots, and any combination of these structures are included. For example, the active layer is configured to generate electromagnetic radiation in the spectral range between infrared and ultraviolet light.

[0009] According to another embodiment of the edge-emitting semiconductor laser diode, the substrate and the epitaxial semiconductor layer stack provided thereon comprise two oppositely facing facets, in particular the facets being side surfaces of the substrate and the epitaxial semiconductor layer stack, which are arranged, for example, perpendicular or inclined with respect to the first main surface of the substrate.

[0010] Preferably, a highly reflective layer is disposed on the facet, hereinafter referred to as the back facet, and is configured to reflect electromagnetic radiation generated during operation, for example, the highly reflective layer reflects at least 90%, preferably at least 99%, of electromagnetic radiation generated during operation that is incident on the layer.

[0011] The facet opposite the back facet is referred to as the extraction facet. The extraction facet is configured to couple electromagnetic radiation generated during operation into the edge-emitting laser diode. An anti-reflection layer is preferably disposed on the extraction facet having a lower reflectivity than the highly reflective layer on the back facet. For example, the anti-reflection layer reflects 10% to 80% of the electromagnetic radiation generated during operation that is incident on the layer.

[0012] In particular, the back facet and the light extraction facet together with the layers provided thereon form an optical cavity, which may also comprise additional optical elements such as an external mirror. During operation, electromagnetic radiation generated in the active layer forms a standing electromagnetic wave in the optical cavity.

[0013] The active layer, in cooperation with the optical cavity, is configured to generate electromagnetic laser radiation, which is generated by stimulated emission and which typically has a very high coherence length, a very narrow spectral linewidth, and / or a high degree of polarization compared to electromagnetic radiation generated by spontaneous emission.

[0014] According to another embodiment, the edge-emitting semiconductor laser diode comprises at least one matching layer disposed on the second main surface of the substrate. For example, the matching layer is provided directly on the second main surface of the substrate. The matching layer preferably comprises or consists of a dielectric material or a semiconductor material. The edge-emitting laser diode may also comprise multiple matching layers.

[0015] According to another embodiment, the edge emitting semiconductor laser diode comprises an absorbing layer disposed directly on the matching layer and configured to at least partially absorb electromagnetic radiation generated during operation. The absorbing layer is preferably provided on the opposite side of the matching layer from the substrate and completely or partially covers the matching layer. In particular, the absorbing layer is configured to at least partially absorb electromagnetic laser modes propagating in the substrate. For example, the absorbing layer may be configured to provide a 100 cm dc to at least 100 cm dc to the electromagnetic radiation generated during operation. -1 , preferably at least 1000 cm -1It has an absorption rate of

[0016] According to another embodiment of the edge-emitting semiconductor laser diode, the substrate and the matching layer are transparent to the electromagnetic radiation generated during operation. In particular, the band gap of the substrate and the band gap of the matching layer are larger than the band gap of the active layer of the epitaxial semiconductor layer stack. For example, the substrate and the matching layer have a transmittance of at least 5%, preferably at least 10%, particularly preferably at least 50% for the electromagnetic radiation generated during operation.

[0017] According to another embodiment of the edge-emitting semiconductor laser diode, the matching layer is configured to increase the absorption of electromagnetic radiation in the absorbing layer. In particular, the matching layer is configured to adjust the phase and the position of the intensity maximum of the laser mode propagating in the substrate, such that the laser mode is highly attenuated in the absorbing layer. For example, the attenuation of the laser mode propagating in the substrate of an edge-emitting semiconductor laser diode with a matching layer is at least one order of magnitude larger, preferably at least two orders of magnitude larger, than an otherwise identical edge-emitting semiconductor laser diode without a matching layer.

[0018] According to a preferred embodiment, the edge-emitting semiconductor laser diode has at least the following characteristics: A substrate having a first main surface and a second main surface opposite the first main surface; an epitaxial semiconductor layer stack provided on a first main surface of a substrate, the epitaxial semiconductor layer stack having an active layer that generates electromagnetic radiation; at least one matching layer disposed on the second major surface of the substrate; an absorbing layer disposed directly on the matching layer and configured to at least partially absorb the electromagnetic radiation; the substrate and the matching layer are transparent to electromagnetic radiation generated during operation; The matching layer is configured to increase absorption of electromagnetic radiation in the absorbing layer.

[0019] In edge-emitting semiconductor laser diodes, the layers of the epitaxial semiconductor layer stack are arranged in particular in such a way that the electromagnetic radiation generated during operation is guided therein and coupled out at the light extraction facet. For example, the active layer is arranged between two cladding layers configured for laterally directing the electromagnetic radiation. Hereinafter, "laterally" means a direction parallel to the first main surface of the substrate.

[0020] Due to scattering due to rough surfaces and / or defects and / or excessively thin cladding layers, part of the electromagnetic radiation generated during operation may be coupled from the semiconductor stack to the substrate. Thus, electromagnetic laser modes may propagate in the transparent substrate, which may act as a waveguide for these laser modes. These electromagnetic laser modes propagating in the substrate, hereinafter also referred to as substrate modes, may also be coupled at the extraction facet of the edge-emitting semiconductor laser diode. The substrate modes lead, for example, to additional peak intensities in the far field of the laser radiation generated during operation. In particular, the substrate modes impair the beam quality of the laser beam emitted from the edge-emitting semiconductor laser diode, and thus the imaging and / or image quality.

[0021] The edge-emitting semiconductor laser diodes described herein are based on the idea of ​​suppressing such substrate modes by providing a suitable layer on the major surface of the substrate opposite the epitaxial semiconductor layer stack.

[0022] For example, the substrate mode is at least partially absorbed by the absorbing layer. However, a highly absorbing absorbing layer, e.g., a metallic absorbing layer, may have a high reflectivity. As a result, the substrate mode may be reflected, especially at the interface with the absorbing layer, limiting and / or preventing the suppression of the substrate mode by the absorbing layer.

[0023] The matching layer adjusts the phase and the position of the maximum intensity of the substrate mode, in particular, so that the substrate mode is attenuated more strongly in the absorbing layer. For example, the attenuation of the substrate mode in a semiconductor laser diode with a matching layer is two orders of magnitude higher than in an otherwise identical semiconductor laser diode without a matching layer. The matching layer is preferably transparent to the electromagnetic radiation generated during operation, and in particular has a higher refractive index than the substrate. Thus, the substrate mode coupled to the matching layer and reflected by the absorbing layer is, for example, completely reflected at the interface between the matching layer and the substrate and deflected towards the absorbing layer. This allows, in particular, to increase the absorption of the electromagnetic radiation in the absorbing layer.

[0024] In combination with an absorbing layer, the matching layer can suppress parasitic substrate modes in a simple and cost-effective manner, which can improve the beam quality, particularly in edge-emitting laser diodes, and thus improve image and quality.

[0025] According to a further embodiment of the edge-emitting semiconductor laser diode, the substrate is a growth substrate for an epitaxial semiconductor layer stack, in particular the epitaxial semiconductor layer stack is epitaxially grown on the substrate.

[0026] According to another embodiment of the edge-emitting semiconductor laser diode, the matching layer reduces the distance between the intensity maximum of the electromagnetic laser mode propagating in the substrate and the absorbing layer. In other words, the matching layer is configured to move the intensity maximum of the electromagnetic laser modes propagating in the substrate closer to the absorbing layer. By reducing the distance between the intensity maximum and the absorbing layer, the absorption of the laser mode propagating in the substrate is advantageously increased.

[0027] Preferably, the effect of the matching layer is not limited to individual selected substrate modes, but instead acts on the majority of electromagnetic laser modes propagating in the substrate.

[0028] According to another embodiment of the edge-emitting semiconductor laser diode, the matching layer suppresses reflection of the electromagnetic laser modes propagating in the substrate at the absorbing layer, thereby increasing in particular the absorption of the electromagnetic laser modes propagating in the substrate at the absorbing layer, for example the thickness of the absorbing layer is set such that the parts of the substrate modes reflected at the interface between the substrate and the matching layer interfere as destructively as possible with the parts of these substrate modes reflected at the interface between the matching layer and the absorbing layer.

[0029] According to another embodiment of the edge-emitting semiconductor laser diode, the refractive index of the matching layer for the electromagnetic radiation generated during operation is greater than the refractive index of the substrate for the electromagnetic radiation generated during operation. Thus, the electromagnetic laser radiation propagating in the substrate can be totally reflected at its interface with the substrate while being coupled into the matching layer. This increases the attenuation of substrate modes, especially in the absorbing layer.

[0030] For example, the refractive index of the matching layer is at least 0.01 greater than the refractive index of the substrate and at most 5 greater. Preferably, the refractive index of the matching layer is at least 0.1 greater than the refractive index of the substrate and at most 1.5 greater. Particularly preferably, the refractive index of the matching layer is at least 0.15 greater than the refractive index of the substrate and at most 0.7 greater.

[0031] According to a further embodiment of the edge-emitting semiconductor laser diode, the extinction coefficient of the matching layer for the electromagnetic radiation generated during operation is at most 2. Preferably, the extinction coefficient of the matching layer is at most 0.7, particularly preferably at most 0.1. The lower the extinction coefficient of the matching layer, the more transparent it is for the electromagnetic radiation generated during operation.

[0032] According to another embodiment of the edge-emitting semiconductor laser diode, the thickness of the matching layer is proportional to the wavelength of the electromagnetic radiation generated during operation and inversely proportional to the refractive index of the matching layer for the electromagnetic radiation generated during operation, where the thickness of the layer refers to the spatial extension in a direction perpendicular to the second major surface of the substrate.

[0033]

number

number

number

[0034] By selecting the thickness of the matching layer according to the above formula, the attenuation of the electromagnetic laser modes propagating in the substrate can be advantageously increased. For example, the matching layer thicknesses specified above reduce the intensity of the substrate modes by 3 to 4 orders of magnitude compared to a corresponding edge-emitting semiconductor laser diode without a matching layer.

[0035] According to further embodiments of the edge-emitting semiconductor laser diode, the matching layer has a lateral structure such 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 segments separated from each other, and / or the matching layer has at least one cut-out. If the matching layer is electrically insulating, a lateral structure of the matching layer is particularly advantageous for electrically contacting the epitaxial semiconductor layer stack via the second main surface of the substrate.

[0036] According to other embodiments 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.

[0037] According to another embodiment, the edge-emitting semiconductor laser diode comprises at least two matching layers disposed between the second major surface of the substrate and the absorbing layer, the matching layers may be composed of different materials or material compositions to improve attenuation and suppression of electromagnetic laser modes propagating in the substrate.

[0038] According to another embodiment of the edge-emitting semiconductor laser diode, the matching layer is electrically conductive, so that the epitaxial semiconductor layer stack can be electrically contacted, in particular via the conductive absorption layer, the conductive matching layer and the conductive substrate.

[0039] According to another embodiment of the edge-emitting semiconductor laser diode, the absorption layer is configured as a contact layer for electrical contact of the epitaxial semiconductor layer stack, i.e. the absorption layer is electrically conductive, which allows reducing the number of steps and therefore the costs when manufacturing the edge-emitting semiconductor laser diode.

[0040] According to other embodiments of the edge-emitting semiconductor laser diode, the absorbing layer comprises a metal, a semiconductor material, or a non-stoichiometric dielectric material.

[0041] According to another embodiment, the semiconductor laser diode further comprises a light blocking layer arranged on a sub-region of the light extraction facet 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 the sub-region of the light extraction facet that includes the substrate. In particular, the light extraction facet does not include a light blocking layer in the region of the active layer.

[0042] The light-shielding layer may comprise or consist of several sub-layers. For example, the light-shielding layer has a transmittance of at most 20% for electromagnetic radiation generated during operation. The light-shielding layer in particular comprises an oxide, an oxynitride or a metal, for example aluminum oxide, silicon oxynitride, titanium, platinum or chromium, or consists of one of these materials.

[0043] According to another embodiment, the edge-emitting semiconductor laser diode comprises a contact layer provided on the absorption layer and configured for electrical contact with the epitaxial semiconductor layer stack. Preferably, the contact layer is arranged directly on the absorption layer. The contact layer, for example, comprises or is formed from a metal. The contact layer is configured for electrical contact of the epitaxial semiconductor layer stack via the second main surface of the substrate.

[0044] Alternatively or additionally, the contact layer can be arranged on the first main surface of the substrate, with another contact layer being arranged, for example, on a main surface of the epitaxial semiconductor layer stack facing away from the substrate.

[0045] According to another embodiment of the edge-emitting semiconductor laser diode, the active layer comprises at least two emission regions arranged laterally adjacent to each other and configured to generate electromagnetic radiation in different wavelength ranges. For example, the emission regions arranged adjacent to each other have different material compositions and thus different bandgaps. Preferably, the emission regions can be electrically contacted independently of each other and thus operated and / or controlled independently of each other. Also, the emission regions of the active layer arranged adjacent to each other can generate electromagnetic radiation in the same wavelength range. For example, the edge-emitting semiconductor laser diode is formed as a laser bar.

[0046] According to another embodiment of the edge-emitting semiconductor laser diode, the matching layer comprises at least two subregions arranged laterally adjacent to each other, each subregion being arranged in a direction perpendicular to the first main surface of the substrate below the emission region. In particular, each emission region of the active layer includes a corresponding subregion of the matching layer on the opposite main surface of the substrate. The subregions of the matching layer may be connected to each other or may be spatially separated from each other.

[0047] According to other embodiments of the edge-emitting semiconductor laser diode, the sub-regions of the matching layer have different materials and / or different thicknesses. If the active layer comprises several emitting regions arranged to generate electromagnetic radiation in different wavelength ranges, the thicknesses of the matching layer in the different sub-regions can be selected, for example, to respectively match the emitter wavelengths of the individual emitting regions.

[0048] Further advantageous embodiments and further developments of the edge-emitting semiconductor laser diode are explained below by way of example embodiments with reference to the figures. [Brief description of the drawings]

[0049] [Figure 1] FIG. 1 is a diagram illustrating the electromagnetic laser emission profile in the far field of an edge-emitting semiconductor laser diode. [Diagram 2] FIG. 2 is a diagram illustrating the electromagnetic laser emission profile in the far field of an edge-emitting semiconductor laser diode. [Diagram 3] FIG. 3 illustrates various schematic diagrams of an edge-emitting semiconductor laser diode according to an exemplary embodiment. [Figure 4] FIG. 4 illustrates various schematic diagrams of an edge-emitting semiconductor laser diode according to an exemplary embodiment. [Diagram 5] FIG. 5 illustrates various schematic diagrams of an edge-emitting semiconductor laser diode according to an exemplary embodiment. [Figure 6] FIG. 6 is a schematic diagram of the mode intensity of the substrate mode as a function of the matching layer thickness. [Figure 7] FIG. 7 is a schematic diagram of the mode intensity of the substrate mode as a function of the matching layer thickness. [Figure 8] FIG. 8 is a schematic diagram of the thickness of a matching layer as a function of the refractive index of the matching layer. [Figure 9] FIG. 9 is a schematic diagram of the mode intensity of the substrate mode as a function of the refractive index of the matching layer. [Figure 10] FIG. 10 is a schematic diagram of the mode intensity of the substrate mode as a function of the extinction coefficient of the matching layer. [Figure 11]FIG. 11 is a schematic cross-sectional view of an edge-emitting semiconductor laser diode according to another illustrative embodiment. [Figure 12] FIG. 12 is a schematic cross-sectional view of an edge-emitting semiconductor laser diode according to another illustrative embodiment. [Figure 13] FIG. 13 is a schematic cross-sectional view of an edge-emitting semiconductor laser diode according to another illustrative embodiment. [Figure 14] FIG. 14 is a schematic cross-sectional view of an edge-emitting semiconductor laser diode according to another illustrative embodiment. [Figure 15] FIG. 15 is a schematic cross-sectional view of an edge-emitting semiconductor laser diode according to another illustrative embodiment. [Figure 16] FIG. 16 is a schematic top view of a second major surface of a substrate of an edge-emitting semiconductor laser diode, according to various illustrative embodiments. [Figure 17] FIG. 17 is a schematic top view of a second major surface of a substrate of an edge-emitting semiconductor laser diode, according to various illustrative embodiments. [Figure 18] FIG. 18 is a schematic top view of a second major surface of a substrate of an edge-emitting semiconductor laser diode, according to various illustrative embodiments. [Figure 19] FIG. 19 is a schematic top view of a second major surface of a substrate of an edge-emitting semiconductor laser diode, according to various illustrative embodiments. [Figure 20] FIG. 20 is a schematic top view of a second major surface of a substrate of an edge-emitting semiconductor laser diode, according to various illustrative embodiments. [Figure 21] FIG. 21 is a schematic top view of a second major surface of a substrate of an edge-emitting semiconductor laser diode, according to various illustrative embodiments. [Figure 22] FIG. 22 is a schematic top view of a second major surface of a substrate of an edge-emitting semiconductor laser diode, according to various illustrative embodiments. [Diagram 23] FIG. 23 is a schematic top view of a second major surface of a substrate of an edge-emitting semiconductor laser diode, according to various illustrative embodiments. [Figure 24]FIG. 24 is a schematic cross-sectional view of an edge-emitting semiconductor laser diode according to another illustrative embodiment. [Diagram 25] FIG. 25 is a schematic cross-sectional view of an edge-emitting semiconductor laser diode according to another illustrative embodiment. [Figure 26] FIG. 26 is a schematic cross-sectional view of an edge-emitting semiconductor laser diode according to another illustrative embodiment. [Figure 27] FIG. 27 is a schematic diagram of substrate mode intensity according to an exemplary embodiment.

[0050] In the various figures, components that are identical, similar or have the same effect are provided with the same reference numbers. The figures and the proportions of the components shown in the figures are not necessarily drawn to scale. Furthermore, the thicknesses of the components, in particular the layers, may be exaggerated and / or enlarged for easier visual presentation and / or understanding.

[0051] Figure 1 shows a cross-section of a laser beam emitted by an edge-emitting laser diode. In particular, the electromagnetic laser light has a Gaussian mode profile 20 with different mode widths in two mutually orthogonal directions. The elliptical region shows additional structures in the coupled laser light caused by electromagnetic laser modes 9 propagating in the substrate 1. These substrate modes 9 can be at least partially coupled out of the edge-emitting semiconductor laser diode and impair the beam quality, leading to, for example, poor image quality.

[0052] 2 shows a mode profile 20 of the electromagnetic laser radiation in the far field of an edge-emitting semiconductor laser diode, where the intensity I of the electromagnetic laser radiation is shown as a function of the emission angle α. In particular, the electromagnetic laser radiation has a Gaussian mode profile 20. Furthermore, the mode profile 20 shows additional peak intensities 24 of the electromagnetic laser radiation caused by electromagnetic laser modes 9 propagating in the substrate 1 and coupled out of the edge-emitting semiconductor laser diode. The edge-emitting semiconductor laser diode described here is based on the idea of ​​significantly suppressing these additional peak intensities 24.

[0053] The edge-emitting semiconductor laser diode according to the exemplary embodiment of Fig. 3 comprises a substrate 1 on which an epitaxial semiconductor layer stack 2 is provided. The epitaxial semiconductor layer stack 2 is provided on a first main surface 6 of the substrate 1 and consists, for example, of a nitride compound semiconductor material. The epitaxial semiconductor layer stack 2 comprises an active layer 3 which generates electromagnetic radiation. Furthermore, the epitaxial semiconductor layer stack 2 comprises cladding layers 10 which guide the electromagnetic laser radiation generated in operation in the active layer 3, the active layer 3 being arranged between two cladding layers 10.

[0054] The substrate 1 is in particular a growth substrate on which the epitaxial semiconductor layer stack 2 is epitaxially grown. For example, the substrate 1 comprises gallium nitride or silicon carbide or consists of one of these materials. The substrate 1 is transparent to the 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. The electromagnetic laser radiation generated during operation can therefore at least partially couple from the active layer 3 into the transparent substrate 1 and propagate in the substrate 1 as electromagnetic laser modes 9.

[0055] The matching layer 4 is provided directly on the second main surface 7 of the substrate 1. The matching layer 4 includes a dielectric material or a semiconductor material that is transparent to the electromagnetic radiation generated during operation. For example, the matching layer 4 includes or consists of gallium phosphide. In particular, the refractive index n of the matching layer 4 for the electromagnetic radiation generated during operation is greater than the refractive index of the substrate 1. For example, the refractive index n of the matching layer 4 is greater than the refractive index of the substrate 1 by at least 0.15 and at most 0.7. In addition, the extinction coefficient k of the matching layer is preferably at most 0.1.

[0056] The absorbing layer 5 is applied directly on the main surface of the matching layer 4 opposite the substrate 1. The absorbing layer 5 has in particular a high absorption coefficient for the electromagnetic radiation generated during operation and is made, for example, from a metal.

[0057] The thickness D of the matching layer 4 is selected such that the substrate mode 9 is absorbed and attenuated as much as possible in the absorbing layer 5. For example, the matching layer 4 suppresses the reflection of the substrate mode 9 in the absorbing layer 5. The thickness D of the matching layer 4 is in particular proportional to the wavelength of the electromagnetic radiation generated during operation and inversely proportional to the refractive index n of the matching layer.

[0058] On the main surface of the epitaxial semiconductor layer stack 2 opposite to the substrate 1, a contact layer 19 for electrical contact of the active layer 3 is arranged. Furthermore, the absorption layer 5 is configured as another contact layer for electrical contact with the active layer 3, and the substrate 1 is electrically conductive. For example, the substrate consists of a doped semiconductor material. The matching layer 4 arranged between the substrate 1 and the absorption layer 5 is electrically conductive or has a lateral structure 11. Respective examples of the lateral structure 11 of the matching layer 4 are shown in Figs. 16 to 23. Due to the lateral structure 11 of the matching layer 4, the edge-emitting semiconductor laser diode in particular has a direct electrically conductive connection between the absorption layer 5 and the substrate 1.

[0059] Opposite sides of the semiconductor laser diode are formed as an extraction facet 15 and a back facet 18 which together form an optical cavity of the edge-emitting semiconductor laser diode. The optical cavity is configured to cooperate with the active layer 3 to generate electromagnetic laser radiation during operation. The electromagnetic laser radiation is coupled out through the extraction facet 15 and emitted from the edge-emitting semiconductor laser diode at an emission angle α. The emission angle α denotes the angle between the surface normal of the extraction facet 15 and the emission direction of the electromagnetic laser radiation generated during operation.

[0060] Figure 4 is a schematic perspective view of an edge-emitting semiconductor laser diode according to the exemplary embodiment of Figure 3. In particular, the epitaxial semiconductor layer stack 2 comprises a ridge waveguide 22 for guiding the electromagnetic radiation generated during operation. The ridge waveguide 22 extends laterally between the light extraction facet 15 and the opposite back facet 18. A contact layer 19 electrically contacting the active layer 3 completely covers the ridge waveguide 22.

[0061] The matching layer 4 covers the second main surface 7 of the substrate 1 only partially. In particular, the region of the second main surface 7 above the ridge waveguide 22 in the vertical direction is covered by the matching layer 4. Here, the matching layer 4 covers an area of ​​the second main surface 7 which extends beyond the ridge waveguide 22 in a lateral direction perpendicular to the main extension direction of the ridge waveguide 22 by preferably at least 30 micrometers, particularly preferably by at least 60 micrometers. The area of ​​the second main surface 7 which is not covered by the matching layer 4 is covered by an absorbing layer 5 which extends over the entire second main surface 7. The absorbing layer 5 is thus arranged to be in direct electrical contact with the conductive substrate 1 and in electrical contact with the semiconductor layer stack 2.

[0062] Figure 5 is a schematic cross-sectional view of the edge-emitting semiconductor laser diode according to the exemplary embodiment of Figure 3 in a plan view of the light extraction facet 15. In particular, the matching layer 4 does not completely cover the second major surface 7 of the substrate 1, but extends laterally beyond the ridge waveguide 22 by at least 30 micrometers on either side.

[0063] 6 shows a schematic diagram of the dependence of the mode intensity S of the substrate mode 9 on the thickness D of the matching layer 4. In particular, the mode intensity S indicates the relative intensity of the substrate mode 9 coupled out of the semiconductor laser diode. The mode intensity S with a value of S=1 corresponds to a semiconductor laser diode without an absorption layer 5 and is marked with an asterisk in FIG. 6. In contrast, a semiconductor laser diode of the same design but with an additional absorption layer 5 but without a matching layer 4 has a lower mode intensity S, shown as a square in FIG. 6.

[0064] 6 further illustrates the mode intensity S of the substrate mode 9 of a semiconductor laser diode comprising an absorbing layer 5 and a matching layer 4 as a function of the thickness D of the matching layer 4. In particular, FIG. 6 illustrates that by appropriately selecting the thickness D of the matching layer 4, the mode intensity S of the substrate mode 9 can be reduced, for example, by two orders of magnitude.

[0065] 7 shows the results of a numerical simulation of the mode strength S of the substrate mode 9 as a function of the thickness D of the matching layer 4. The mode strength S has several approximately periodic minima 21. The first minimum 21 occurs at a thickness D of the matching layer 4 designated as D0. The other minima 21 occur at

number

number

[0066] 8 shows the thickness D0 at which the first minimum 21 of the mode intensity S in FIG. 5 occurs as a function of the refractive index n of the matching layer 4. The thickness D0 is given by the function

number

[0067] 9 shows numerical results for the mode intensity S of the substrate mode 9 as a function of the refractive index n of the matching layer 4, with the thickness D of the matching layer 4 and the optical properties of the absorbing layer 5 fixed. In particular, FIG. 7 shows that the mode intensity S of the substrate mode 9 contains a strong and pronounced minimum 21 at a certain value of the refractive index n of the matching layer 4. This value depends, among other things, on the optical properties of the absorbing layer 5, in particular on the complex refractive index of the absorbing layer 5.

[0068] Figure 10 shows the mode intensity S of the substrate mode 9 as a function of the extinction coefficient k of the matching layer 4, with the thickness D and the refractive index n of the matching layer 4 and the optical properties of the absorbing layer 5 fixed. In particular, Figure 8 shows that the mode intensity S of the substrate mode 9 is particularly low when the extinction coefficient k of the matching layer 4 is at a minimum. In other words, when the extinction coefficient k of the matching layer 4 is at a minimum, the effect is that the attenuation of the substrate mode 9 is high.

[0069] In comparison with the semiconductor laser diode of Fig. 3, the edge-emitting semiconductor laser diode according to the exemplary embodiment of Fig. 11 comprises several matching layers 4 arranged between the substrate 1 and the absorbing layer 5. The different matching layers 4 are, for example, made of different materials and thus have different optical properties, in particular different refractive indices n. As a result, the attenuation of the substrate mode 9 can be fine-tuned and improved.

[0070] Compared to the semiconductor laser diode of Fig. 3, the edge-emitting semiconductor laser diode according to the exemplary embodiment of Fig. 12 further comprises a light-shielding layer 14. The light-shielding layer 14 partially covers the light extraction facet 15, in particular in the region of the substrate 1. The light-shielding layer 14 is configured for at least partial absorption and / or reflection of the substrate mode 9. Thereby, the coupling of the substrate mode 9 from the semiconductor laser diode is at least partially reduced or prevented. The combination of the matching layer 4 and the absorption layer 5 allows an even greater suppression of the substrate mode 9 in the far field of the laser radiation coupled by the semiconductor laser diode.

[0071] 5, the exemplary embodiment of FIG. 13 comprises a matching layer 4 that completely covers the second major 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 through the electrically conductive substrate 1.

[0072] In comparison with the edge-emitting semiconductor laser diode of Fig. 13, in the exemplary embodiment of the edge-emitting semiconductor laser diode of Fig. 14 the absorption layer 5 is not configured as a contact layer. As a result, the electrically conductive matching layer 4 and the electrically conductive substrate 1 are not required for electrical contact of the epitaxial semiconductor layer stack 2. Instead, a contact layer 19 for electrical contact of the epitaxial semiconductor layer stack 2 is arranged parallel to the ridge waveguide 22 and laterally spaced apart from the epitaxial semiconductor layer stack 2 not only on the first main surface 6 of the substrate 1 but also on the main surface of the epitaxial semiconductor layer stack 2 facing away from the substrate 1.

[0073] In the edge-emitting semiconductor laser diode according to the exemplary embodiment of Fig. 15, the area where the absorption layer 5 is in direct contact with the second major surface 7 of the substrate 1 is larger than in the edge-emitting semiconductor laser diode of Fig. 12. This can result in improved electrical contact between the absorption layer 5 and the substrate 1 in the case of a non-conductive matching layer 4.

[0074] 16 is a top view of the second main surface 7 of the substrate 1 of an edge-emitting semiconductor laser diode, where the second main surface 7 is partially free of the matching layer 4 and the absorbing layer 5 extends over the entire second main surface 7. In particular, the region at the edge of the second main surface 7, which extends between the light extraction facet 15 and the back facet 18, does not include the matching layer 4.

[0075] In the edge emitting semiconductor laser diode of FIG. 17, the two regions at both ends of the second main surface 7 do not include a matching layer 4, as compared with FIG.

[0076] 17, in FIG. 18 the absorbing layer 5 does not completely cover the substrate 1. On the other hand, the matching layer 4 is completely covered by the absorbing layer 5.

[0077] In FIG. 19, in comparison to FIG. 18, the matching layer 4 and the absorbing layer 5 are laterally spaced from the extraction facet 15 and the back facet 18.

[0078] Compared to the edge-emitting semiconductor diode of Fig. 19, the matching layer 4 of Fig. 20 includes an additional lateral structure 11. In particular, the matching layer 4 includes a plurality of mutually separated segments 12 arranged along a direction between the light extraction facet 15 and the back facet 18.

[0079] In the edge emitting semiconductor laser diode of FIG. 21, in comparison with FIG. 17, only a sub-region of the second main surface 7 at the light extraction facet 18 is covered by the matching layer 4.

[0080] Compared to the edge-emitting semiconductor laser diode of FIG. 20, the edge-emitting semiconductor laser diode of FIG. 22 comprises a lateral structure 11 of the matching layer 4 consisting of a number of cutouts 13.

[0081] The edge-emitting semiconductor laser diode of Figure 23 comprises an absorption layer 5 comprising two segments 12 separated from each other. The two segments 12 are located near the extraction facet 15 and the back facet, while the matching layer 4 covers the area of ​​the second main surface 7 adjacent to the extraction facet 15.

[0082] 24 is a top view of the light extraction facet 15 of an edge-emitting semiconductor laser diode. The epitaxial semiconductor layer stack 2 comprises three laterally spaced apart emission regions 16. 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 sub-region 17 of the absorption layer 5 and matching layer 4 is provided on the second main surface 7 of the substrate 1 diametrically arranged with respect to the respective emission region 16.

[0083] Compared to Fig. 24, the sub-regions 17 of the matching layer 4 of the edge-emitting semiconductor laser diode of Fig. 25 have different properties. For example, the matching layer 4 has a different thickness D and / or a different material composition in the sub-regions 17. This allows the matching layer 4 in the sub-regions 17 to be adapted, for example, to different emission wavelengths of different emitting regions 16.

[0084] Figure 26 shows, in comparison with figure 24, an edge-emitting semiconductor laser diode with a continuous matching layer 4. In particular, the matching layer 4 is not divided into separate sub-regions 17. Thereby, all emitting regions 16 of the semiconductor layer stack 2 share a common matching layer 4.

[0085] 27 is a schematic diagram of the intensity I of the substrate mode 9 in a direction R perpendicular to the second main surface 7 of the substrate 1. The substrate mode 9 is shown as a standing electromagnetic wave in the direction R. At the interface between the matching layer 4 and the metallic absorbing layer 5, the substrate mode 9 contains in particular a node where the intensity I of the substrate mode 9 vanishes. The matching layer 4 brings the maximum intensity 23 of the substrate mode 9 closer to the absorbing layer 5. This has the effect of increasing the attenuation of the substrate mode 9 in the absorbing layer 5.

[0086] This patent application claims priority to German patent application DE102022104418.1, the disclosure of which is incorporated herein by reference.

[0087] The invention is not limited by its description to the exemplary embodiments, but instead includes any novel feature and any combination of features, specifically including any combination of features in the claims, even if this feature or combination itself is not explicitly recited in the claims or in the exemplary embodiments. [Explanation of symbols]

[0088] 1 Board 2. Epitaxial semiconductor layer stack 3 Active layer 4 Matching layer 5 Absorption Layer 6 First main surface 7 Second main surface 8 distance 9 Substrate Mode 10 Cladding Layer 11. Structure 12 Segments 13 Recess 14 Light blocking layer 15 Light extraction facet 16 Output area 17 Sub-areas 18 Back Facet 19 Contact layer 20 Mode Profiles 21 Minimum 22 Ridge Waveguide 23 maximum strength 24 Peak Intensity I strength S-mode intensity n Refractive Index k Extinction coefficient D Thickness α radiation angle R direction

Claims

1. A substrate (1) having a first main surface (6) and a second main surface (7) opposite to the first main surface (6); an epitaxial semiconductor layer stack (2) provided on a first main surface (6) of the substrate (1) and comprising an active layer (3) for generating electromagnetic radiation; At least one matching layer (4) disposed on the second major surface (7) of the substrate (1); an absorbing layer (5) disposed directly on the matching layer (4) and configured to at least partially absorb electromagnetic radiation; The substrate (1) and the matching layer (4) are transparent to electromagnetic radiation generated during operation; The matching layer (4) is configured to increase the absorption of electromagnetic radiation in the absorbing layer (5). Edge-emitting semiconductor laser diode.

2. The substrate (1) is a growth substrate for the epitaxial semiconductor layer stack (2), 2. An edge-emitting semiconductor laser diode according to claim 1.

3. The matching layer (4) reduces the distance (8) between the maximum intensity (23) of an electromagnetic laser mode (9) propagating in the substrate (1) and the absorbing layer (5).

3. An edge-emitting semiconductor laser diode according to claim 1 or 2.

4. The matching layer (4) suppresses reflections of electromagnetic laser modes (9) propagating in the substrate (1) at the absorbing layer (5).

4. An edge-emitting semiconductor laser diode according to claim 1.

5. the refractive index (n) of the matching layer (4) for electromagnetic radiation generated during operation is greater than the refractive index of the substrate (1) for electromagnetic radiation generated during operation; 5. An edge-emitting semiconductor laser diode according to claim 1.

6. the extinction coefficient (k) of the matching layer (4) for electromagnetic radiation generated during operation is at most 2; 6. An edge-emitting semiconductor laser diode according to claim 1.

7. The thickness (D) of the matching layer (4) is proportional to the wavelength of the electromagnetic radiation generated during operation and inversely proportional to the refractive index (n) of the matching layer (4) for the electromagnetic radiation generated during operation.

7. An edge emitting semiconductor laser diode according to claim 1. 【Request 8】 【Number 7】 and [0080] where m is an integer equal to or greater than 0, λ is the wavelength of electromagnetic radiation generated during operation, n is the refractive index of the matching layer (4) for the electromagnetic radiation generated during operation, and n Ｓｕｂｓｔｒａｔｅ is the refractive index of the substrate (1) for electromagnetic radiation generated during operation, The thickness (D) of the matching layer (4) is [0090] The tolerance is ±30 nanometers.

8. An edge emitting semiconductor laser diode according to claim 1.

9. the matching layer (4) comprises a lateral structure (11) such that only a portion of the second main surface (7) of the substrate is covered by the matching layer, and / or the matching layer (4) comprises at least two segments (12) separated from each other, and / or the matching layer (4) comprises at least one cutout (13); 9. An edge emitting semiconductor laser diode according to claim 1.

10. The matching layer (4) comprises titanium oxide, non-stoichiometric silicon oxide, non-stoichiometric silicon nitride, silicon carbide, or gallium phosphide; 10. An edge emitting semiconductor laser diode according to claim 1.

11. The matching layer (4) is electrically conductive.

11. An edge-emitting semiconductor laser diode according to claim 1.

12. The absorption layer (5) is configured as a contact layer (19) for electrical contact of the epitaxial semiconductor layer stack (2).

12. An edge-emitting semiconductor laser diode according to claim 1.

13. The absorbing layer (5) comprises a metal, a semiconductor material, or a non-stoichiometric dielectric material.

13. An edge-emitting semiconductor laser diode according to claim 1.

14. a light shielding layer (14) arranged on a sub-region of a light extraction facet (15) of the semiconductor laser diode and configured to at least partially absorb and / or reflect an electromagnetic laser mode (9) propagating in the substrate (1), 14. An edge-emitting semiconductor laser diode according to claim 1.

15. the active layer (3) comprises at least two emission regions (16) arranged laterally adjacent to each other and configured to generate electromagnetic radiation in different wavelength ranges, 15. An edge-emitting semiconductor laser diode according to claim 1.

16. The matching layer (4) comprises at least two sub-regions (17) arranged laterally adjacent to each other, Each sub-region (17) is disposed below the emission region (16) in a direction perpendicular to the first main surface (6) of the substrate (1); 16. An edge-emitting semiconductor laser diode according to claim 15.

17. The sub-regions (17) of the matching layer (4) have different materials and / or different thicknesses (D).

17. An edge-emitting semiconductor laser diode according to claim 16.

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