Semiconductor laser and method for manufacturing a semiconductor laser

Abstract

A semiconductor laser with the following characteristics is specified: - an epitaxial semiconductor layer sequence (2) based on a nitride compound semiconductor material comprising a p-doped region (5) and an n-doped region (6) as well as an active zone (7) arranged between the p-doped region (5) and the n-doped region (6), and - a mode-shifting layer (13) located within or adjacent to the n-doped region (6), where - the mode-shifting layer (13) positions a mode (25) of the electromagnetic laser radiation (20) such that it overlaps with a gain region (8) of the epitaxial semiconductor layer sequence (2) during operation, wherein the gain region (8) is configured to generate electromagnetic laser radiation (20) during operation, - the mode-shifting layer (13) has at least one via (16). Furthermore, a method for manufacturing a semiconductor laser is provided.

Description

[0001] A semiconductor laser and a method for manufacturing a semiconductor laser are described.

[0002] The object of this application is to provide an improved semiconductor laser, in particular an improved edge-emitting semiconductor laser and an improved surface-emitting photonic crystal laser. Furthermore, an improved method for fabricating a semiconductor laser is to be provided.

[0003] These problems are solved by a semiconductor laser having the features of claim 1 and a method having the steps of claim 14.

[0004] Improved embodiments and further developments of the semiconductor laser and the method for manufacturing a semiconductor laser are specified in the dependent claims. In particular, the semiconductor laser is a semiconductor laser diode.

[0005] According to one embodiment, the semiconductor laser comprises an epitaxial semiconductor layer sequence based on a nitride compound semiconductor material. Nitride compound semiconductor materials are nitrogen-containing compound semiconductor materials, such as the materials from the system In x Al y Ga 1-x-y N with 0≤ x≤ 1, 0≤ y≤ 1 and x+y≤ 1. In particular, AlGaN with x=0, InGaN with y=0 and GaN with x=y=0 are nitride compound semiconductor materials.

[0006] Furthermore, (Al)GaN denotes x=0 and 0≤ y≤ 1. In other words, the nitride compound semiconductor material designated (Al)GaN does not contain indium, and aluminum is optionally present as a component. In particular, the epitaxial semiconductor layer sequence comprises a plurality of epitaxially grown semiconductor layers stacked one above the other in a growth direction. The growth direction is perpendicular to a principal extension plane of the epitaxial semiconductor layer sequence. In particular, the epitaxial semiconductor layer sequence has a first principal surface and an oppositely arranged second principal surface, wherein the first principal surface and the second principal surface are parallel to each other and to the principal extension plane. In particular, the first principal surface and the second principal surface are perpendicular to the growth direction.

[0007] According to one embodiment of the semiconductor laser, the epitaxial semiconductor layer sequence comprises a p-doped region and an n-doped region, as well as an active zone located between the p-doped region and the n-doped region.

[0008] In particular, the active zone for generating electromagnetic radiation is set up during operation. The active zone comprises, for example, a pn junction, a double heterostructure, a single quantum well structure, or a multiple quantum well structure for generating the electromagnetic radiation.

[0009] According to a further embodiment of the semiconductor laser, the semiconductor laser comprises a mode-shifting layer located within or adjacent to the n-doped region. In particular, the mode-shifting layer is part of the epitaxial semiconductor layer sequence and is grown epitaxially like the other epitaxial semiconductor layers of the sequence. Specifically, the mode-shifting layer comprises or consists of a nitride compound semiconductor material.

[0010] According to a further embodiment of the semiconductor laser, the mode-shifting layer localizes a mode of electromagnetic laser radiation during operation such that it overlaps with an amplification region of the epitaxial semiconductor layer sequence, the amplification region being configured to generate electromagnetic laser radiation. In particular, the amplification region comprises at least a portion of the active zone. Specifically, the mode of electromagnetic laser radiation localized by the mode-shifting layer is a predetermined mode of electromagnetic laser radiation.

[0011] The active zone is specifically designed to generate electromagnetic radiation from an electric current flowing through it. Within the semiconductor laser, the active zone is at least partially configured as a laser-active medium. During operation, electromagnetic laser radiation is generated within this laser-active medium due to the amplification and / or selection of predetermined modes of the electromagnetic laser radiation. In particular, the propagation direction of the electromagnetic laser beam within the epitaxial semiconductor layer sequence is perpendicular to the growth direction of the epitaxial semiconductor layer sequence.

[0012] For example, a semiconductor laser includes an optical resonator for amplifying and / or selecting modes of electromagnetic laser radiation, within which the laser-active medium, such as the active zone, is located. The active zone alone is designed to generate electromagnetic radiation by spontaneous emission. When the active zone is located within the optical resonator, population inversion is achieved within the region of the active zone that encompasses the amplification region, and electromagnetic laser radiation is generated by stimulated emission. In particular, electromagnetic laser radiation generated by stimulated emission exhibits a long coherence length, a narrow emission spectrum, and a high degree of polarization compared to electromagnetic radiation generated by spontaneous emission.

[0013] During operation of the semiconductor laser, a multitude of optical modes of electromagnetic laser radiation are generated within the optical resonator; these are intrinsic solutions of the optical resonator. In particular, a fundamental mode of electromagnetic laser radiation is generated within the optical resonator. Specifically, the semiconductor laser emits electromagnetic laser radiation of a single mode, in particular the fundamental mode. For example, the electromagnetic laser radiation is blue and / or green electromagnetic laser radiation.

[0014] Furthermore, the semiconductor laser may include a photonic crystal layer containing a photonic crystal to enhance and / or select the modes of the electromagnetic laser radiation. Photonic crystals exhibit a photonic band gap for photons, corresponding to the electronic band gap of semiconductors for charge carriers. Photons with energies within the photonic band gap cannot propagate within the photonic crystal and are reflected by it. The photonic band gap arises wholly or partially from periodic structures of at least two materials within the photonic crystal. In this case, the photonic crystal of the photonic crystal layer is, in particular, a two-dimensional photonic crystal in which the periodic structures are periodic in two spatial directions.The photonic crystal layer is located near the active zone and, in particular, near the part of the active zone encompassed by the amplification region, and leads to a stimulated emission of electromagnetic laser radiation within the part of the active zone encompassed by the amplification region.

[0015] In particular, the mode-shifting layer is configured to shift a mode of the semiconductor laser, especially the fundamental mode, so that it overlaps with the gain region. In other words, the mode of the semiconductor laser exhibits less overlap with the gain region within the epitaxial semiconductor layer sequence without the mode-shifting layer than within an epitaxial semiconductor layer sequence with the mode-shifting layer. The mode-shifting layer, in particular, leads to a higher efficiency of the semiconductor laser. Specifically, the mode-shifting layer has a lower refractive index than the surrounding semiconductor material, which causes the modes of the electromagnetic laser radiation to be pushed back to overlap with the gain region. In particular, the mode-shifting layer is intentionally undoped or n-doped.

[0016] According to a further embodiment of the semiconductor laser, the mode-shifting layer has at least one via. In particular, the via is configured for the flow of electric current through the mode-shifting layer. Specifically, the at least one via completely penetrates the mode-shifting layer. For example, the via is filled with semiconductor material of the epitaxial semiconductor layer sequence. For example, the diameter of the at least one via does not exceed 10 micrometers or 2 micrometers. In particular, it is not necessary for one side face of the via to be completely closed. For example, a volume of the via on one side face of the epitaxial semiconductor layer sequence is freely accessible.

[0017] According to another embodiment of the semiconductor laser, the mode-shifting layer comprises a plurality of vias. For example, the vias may be identical or different. For example, the vias within the mode-shifting layer may be randomly or systematically distributed. For example, two directly adjacent vias may be equidistant from each other, or the distance between two directly adjacent vias may vary across the mode-shifting layer. For example, the distance between two directly adjacent vias may be larger in an outer region of the mode-shifting layer and decrease continuously from the outer region to a central region of the mode-shifting layer.For example, the at least one via has a side surface that is inclined or perpendicular with respect to the growth direction of the epitaxial semiconductor layer sequence.

[0018] According to another embodiment, the semiconductor laser comprises: - the epitaxial semiconductor layer sequence based on the nitride compound semiconductor material, comprising the p-doped region and the n-doped region and the active zone located between the p-doped region and the n-doped region, and - the mode-shifting layer located within or adjacent to the n-doped region, where - the mode-shifting layer positions the mode of the electromagnetic laser radiation so that it overlaps with the gain region of the epitaxial semiconductor layer sequence during operation, and - the mode-shifting layer which has at least one via.

[0019] In this case, the epitaxial semiconductor layer sequence is provided with the mode-shifting layer to shift the predetermined mode of the electromagnetic laser radiation so that it overlaps with the gain region in order to improve the efficiency of the semiconductor laser.

[0020] Often, a mode-shifting layer material suitable for the desired mode shift of the electromagnetic laser radiation simultaneously leads to an increased voltage drop across the epitaxial semiconductor layer sequence. Semiconductor lasers are based, among other things, on the idea of ​​providing the mode-shifting layer with at least one via, thereby enabling increased current flow through the via to reduce the voltage drop. Specifically, the via is filled with a semiconductor material that exhibits higher electrical conductivity compared to the mode-shifting layer material. For example, the mode-shifting layer material is undoped, while the material filled into the via is doped, particularly n-doped. The mode-shifting layer with the via, in particular, ensures a reduced electrical resistance of the semiconductor laser.

[0021] According to one embodiment of the semiconductor laser, the n-doped region comprises an n-doped cladding layer, and the mode-shifting layer is located within or adjacent to, in particular directly adjacent to, the n-doped cladding layer. For example, the mode-shifting layer is in direct contact with the n-doped cladding layer and shares a common interface with it. For example, the n-doped cladding layer comprises or consists of n-doped GaN or n-doped AlGaN. In particular, the n-doped cladding layer has a refractive index that is greater than the refractive index of the mode-shifting layer and less than the refractive index of the active region. For example, the n-doped cladding layer has a thickness between and including 500 nanometers and 3 micrometers.In particular, the n-doped cladding layer suppresses the propagation of electromagnetic laser modes in a semiconductor laser substrate, especially in a growth substrate of the epitaxial semiconductor layer sequence. The mode-shifting layer makes it possible to reduce the thickness of the n-doped cladding layer to such an extent that the epitaxial semiconductor layer sequence, in particular, exhibits a reduced voltage.

[0022] According to another embodiment of the semiconductor laser, the mode-shifting layer extends continuously along the gain region. In other words, when viewed from above the epitaxial semiconductor layer sequence, the one or more vias within the mode-shifting layer are arranged laterally to the gain region. A region of the mode-shifting layer along the gain region is free of vias. In particular, the region of the mode-shifting layer that is located below the gain region when viewed from above is free of vias. For example, in the case of an edge-emitting laser with a waveguide, the region below the waveguide, viewed from above, is free of vias.This has the advantage that the modes of the electromagnetic laser radiation are shifted particularly efficiently so that they overlap with the amplification area, while at the same time the electrical current flow through the active zone is improved.

[0023] According to another embodiment of the semiconductor laser, the mode-shifting layer comprises or consists of AlInN and / or AlGaN and / or AlInGaN. Particularly preferably, the mode-shifting layer comprises or consists of AlInN. For example, the mode-shifting layer is intentionally undoped or n-doped. For example, the mode-shifting layer has a refractive index of at most 2.35 or at most 2.30. It is also possible for the refractive index to be slightly higher.

[0024] According to a further embodiment of the semiconductor laser, the mode-shifting layer has an indium content between 15% and 20% inclusive, preferably between 16% and 19%, and particularly preferably between 17% and 18%. In particular, the mode-shifting layer comprises or consists of AlInN and has an indium content between 16% and 19% inclusive. In particular, the semiconductor material of the mode-shifting layer is lattice-matched to the surrounding semiconductor material. This is achieved in particular with an indium content between 16% and 19% inclusive, and especially of about 18%.

[0025] According to another embodiment of the semiconductor laser, the mode-shifting layer has a thickness of at most 100 nanometers, or at most 200 nanometers, or at most 500 nanometers. It is advantageous to use a mode-shifting layer with a very small thickness, as this reduces the voltage drop across the epitaxial semiconductor layer sequence.

[0026] According to another embodiment of the semiconductor laser, the mode-shifting layer is a mode-shifting layer stack with two or more individual layers. In other words, the mode-shifting layer comprises two or more individual layers that differ in their material composition. For example, one individual layer of the mode-shifting layer stack comprises AlInN and another individual layer of the mode-shifting layer stack comprises (Al)GaN. In other words, one individual layer of the mode-shifting layer stack comprises a nitride semiconductor compound material with indium, while the other individual layer of the mode-shifting layer stack is free of indium.

[0027] According to another embodiment of the semiconductor laser, the n-doped region further comprises a first n-(Al)GaN layer located between the mode-shifting layer and the substrate of the semiconductor laser. In particular, the substrate of the semiconductor laser is the growth substrate of the epitaxial semiconductor layer sequence and comprises or consists of GaN. For example, the first n-(Al)GaN layer is deposited directly onto the substrate. More specifically, the first n-(Al)GaN layer is grown epitaxially on a growth area of ​​the growth substrate. If the first n-(Al)GaN layer is provided within the epitaxial semiconductor layer sequence, the thickness of the mode-shifting layer can be advantageously reduced.

[0028] According to one embodiment of the semiconductor laser, the n-doped region further comprises a second n-(Al)GaN layer, and the mode-shifting layer is arranged between the first n-(Al)GaN layer and the second n-(Al)GaN layer. In other words, the mode-shifting layer is located between the two n-(Al)GaN layers. This arrangement leads, in particular, to an improved shift of the electromagnetic laser modes.

[0029] According to a further embodiment of the semiconductor laser, a current distribution layer is arranged between the active zone and the mode-shifting layer. In particular, the current distribution layer is configured to distribute an electric current within the epitaxial semiconductor layer sequence, and especially within the active zone. Preferably, the current distribution layer extends continuously within the epitaxial semiconductor layer sequence along its main extension plane. For example, the current distribution layer comprises or consists of InGaN, AlGaN, or GaN. For example, the current distribution layer comprises or consists of a superlattice of alternating layers. For example, the superlattice comprises or consists of alternating (Al)GaN layers and GaN layers, or of alternating InGaN layers and GaN layers.

[0030] According to another embodiment of the semiconductor laser, facets delimit the epitaxial semiconductor layer sequence on oppositely arranged side surfaces, wherein the facets are arranged perpendicular to the propagation direction of the electromagnetic laser radiation within the epitaxial semiconductor layer sequence.

[0031] In particular, the facets form the optical resonator of the semiconductor laser. The active region is located within the optical resonator as the laser-active medium, and during operation of the semiconductor laser, a population inversion is achieved in the portion of the active region encompassed by the gain region. The electromagnetic laser radiation generated within the gain region by stimulated emission propagates in the direction of propagation between the facets of the semiconductor laser.

[0032] In particular, one of the facets is provided with a highly reflective layer that is highly reflective to the electromagnetic laser radiation, while the other facet is provided with a partially transparent layer that is partially transparent to the electromagnetic laser radiation, so that electromagnetic laser radiation is coupled out of this facet during operation. In this embodiment, the semiconductor laser is, in other words, an edge-emitting semiconductor laser.

[0033] According to a further embodiment, the semiconductor laser comprises a photonic crystal layer that amplifies and / or selects modes of the electromagnetic laser radiation. In particular, the photonic crystal layer comprises or consists of a two-dimensional photonic crystal. In this embodiment, the semiconductor laser specifically does not include facets that form the optical resonator for mode amplification and / or mode selection, but rather a photonic crystal layer with a photonic crystal for mode amplification and / or mode selection. The photonic crystal layer specifically amplifies and / or selects modes of the electromagnetic laser radiation that propagate along the direction of propagation perpendicular to a growth direction of the epitaxial semiconductor layer sequence.In particular, the propagation direction of the electromagnetic laser radiation is perpendicular to the side surfaces of the epitaxial semiconductor layer sequence, as in the case of the edge-emitting semiconductor laser.

[0034] Furthermore, the photonic crystal deflects in particular a portion of the electromagnetic laser radiation propagating within the amplification region onto a radiation output surface of the semiconductor laser, which is in particular part of a first principal surface or a second principal surface of the semiconductor laser.

[0035] The semiconductor laser with the photonic crystal layer for amplifying and / or selecting modes of the electromagnetic laser radiation is in particular a photonic surface-emitting semiconductor laser (PCSEL for short).

[0036] In particular, the photonic crystal layer is part of the p-doped region of the epitaxial semiconductor layer sequence. The mode-shifting layer positions the modes of the electromagnetic laser radiation so that they overlap not only with the gain region of the epitaxial semiconductor layer sequence, but also with the photonic crystal layer of the PCSEL.

[0037] The photonic crystal layer is oriented parallel to the main extension plane of the epitaxial semiconductor layer sequence. For example, the photonic crystal layer is part of the epitaxial semiconductor layer sequence, and parts of the photonic crystal layer are grown epitaxially. For example, the photonic crystal layer is fabricated from an epitaxially grown semiconductor layer that, after epitaxial growth, is equipped with periodically arranged structural elements, such as holes. For example, the holes extend along the growth direction of the epitaxial semiconductor layer sequence and are arranged at periodic intervals within the p-region. The holes can be filled with another material, such as a dielectric material.The holes and / or the material within the holes exhibit, in particular, a high refractive index difference compared to the surrounding semiconductor material of the p-doped region.

[0038] According to one embodiment of the semiconductor laser, the photonic crystal layer comprises periodically arranged structural elements and a plurality of vias within the mode-shifting layer, which are also periodically arranged. In particular, the periodicity of the vias is at least 10 times greater than the periodicity of the structural elements of the photonic crystal layer.

[0039] In particular, the substrate is provided with an n-contact layer, which, for example, comprises or consists of a metal. If the semiconductor laser is an edge-emitting semiconductor laser, a further p-contact is arranged on or above the p-doped region, establishing an electrical contact with the p-doped region. In this way, during operation, an electric current flows along the growth direction through the epitaxial semiconductor layer sequence.

[0040] According to one embodiment, the semiconductor laser, configured as an edge-emitting semiconductor laser, comprises a bridge waveguide etched into the epitaxial semiconductor layer sequence, particularly into the p-doped region of the epitaxial semiconductor layer sequence. The amplification region, viewed from above, overlaps the bridge waveguide, preferably completely. In particular, the p-contact layer is arranged on the bridge waveguide.

[0041] According to one embodiment, the p-contact layer is arranged, for example, on or above the photonic crystal layer and, in particular, completely covers the photonic crystal layer. For example, the p-contact layer is configured as a mirror for the electromagnetic laser radiation. The p-contact layer can comprise or consist of a metal.

[0042] In the case that the semiconductor laser is configured as a PCSEL and includes a photonic crystal layer for mode selection and / or mode amplification, the n-contact layer is, for example, located in an outer region of the substrate surrounding a centrally located radiation exit surface. It is also possible that the photonic crystal layer includes a mesa that penetrates the p-doped region and the active zone, thus providing access to the n-doped region of the epitaxial semiconductor layer sequence. In this case, the n-contact layer is specifically located within the vias on the n-doped region for electrical contact.

[0043] Semiconductor lasers are used, for example, in augmented reality (AR) / virtual reality (VR) devices such as AR / VR glasses. Furthermore, semiconductor lasers can be used as high-power lasers for projections and material processing.

[0044] The semiconductor laser described here can be manufactured using the method disclosed below. Therefore, features and embodiments disclosed in connection with the semiconductor laser can also be implemented in the method, and vice versa.

[0045] According to one embodiment of the method for fabricating a semiconductor laser, a substrate is provided. In particular, the substrate is a growth substrate and is configured for the epitaxial growth of an epitaxial semiconductor layer sequence. Specifically, the epitaxial semiconductor layer sequence to be epitaxially grown on the growth substrate is based on a nitride compound semiconductor material. For example, the growth substrate comprises or consists of GaN, sapphire, and / or silicon carbide. The growth substrate particularly has a growth area configured for the epitaxial growth of the epitaxial semiconductor layer sequence. For example, the growth area is a c-plane of the growth substrate.

[0046] According to a further embodiment of the method, an epitaxial semiconductor layer sequence based on a nitride compound semiconductor material is epitaxially grown on the growth substrate. In particular, the epitaxial semiconductor layer sequence comprises a p-doped region and an n-doped region, as well as an active zone located between the p-doped region and the n-doped region. The active zone is specifically configured to generate electromagnetic radiation by spontaneous emission.

[0047] According to a further embodiment of the method, a mode-shifting layer is arranged within or adjacent to the n-doped region. In particular, the mode-shifting layer is part of the epitaxial semiconductor layer sequence and is therefore also grown epitaxially on the growth substrate.

[0048] According to a further embodiment of the method, the mode-shifting layer positions a mode of the electromagnetic laser radiation such that it overlaps with an amplification region of the epitaxial semiconductor layer sequence during operation. In particular, the mode-shifting layer has at least one via.

[0049] According to a preferred embodiment, the method for manufacturing the semiconductor laser comprises the following steps: - Providing the substrate, - epitaxial growth of the epitaxial semiconductor layer sequence based on the nitride compound semiconductor material on the growth substrate, wherein the epitaxial semiconductor layer sequence comprises the p-doped region and the n-doped region as well as the active zone arranged between the p-doped region and the n-doped region, wherein - the mode-shifting layer is located within or adjacent to the n-doped region, - the mode-shifting layer positions the mode of the electromagnetic laser radiation so that it overlaps with the gain region of the epitaxial semiconductor layer sequence during operation, - the mode-shifting layer which has at least one via, in particular for the passage of electric current.

[0050] In particular, these steps are carried out in the specified order.

[0051] According to a further embodiment of the method, the at least one via is etched into the mode-shifting layer after its epitaxial growth. In other words, the mode-shifting layer is first grown epitaxially, in particular completely covering the growth substrate, and then the at least one via is etched after the epitaxial growth of the mode-shifting layer. The etching of the mode-shifting layer to create the vias is carried out, for example, by chemical dry etching.

[0052] According to a further embodiment of the method, an (Al)GaN layer is epitaxially grown on the mode-shifting layer with the at least one via. In other words, after the vias are placed within the mode-shifting layer, the (Al)GaN layer is epitaxially grown on the mode-shifting layer. During the growth of the (Al)GaN layer on the mode-shifting layer, the material of the (Al)GaN layer fills the vias, preferably completely. For example, the (Al)GaN layer above the mode-shifting layer has a thickness between 50 nanometers and 250 nanometers inclusive, and further, for example, between 50 nanometers and 150 nanometers inclusive.

[0053] According to a further embodiment of the method, the (Al)GaN layer is epitaxially regrowthed using a low-temperature process. In particular, the epitaxial regrowth of the (Al)GaN layer takes place during an epitaxial process at a temperature of no more than 950 °C, preferably no more than 900 °C.

[0054] Further advantageous embodiments and developments of the semiconductor laser and the method for manufacturing a semiconductor laser result from the exemplary embodiment described below in conjunction with the figures. The Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. Figure 7 shows schematic representations of a semiconductor laser according to several exemplary embodiments. The Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12 to Fig. Figure 13 shows schematic sectional views of steps in a process for manufacturing a semiconductor laser according to an exemplary embodiment.

[0055] Identical or similar elements, as well as elements with the same function, are marked with the same reference symbols in the figures. The figures and the proportions of the elements shown in the figures are not to be considered as being to scale. Rather, individual elements, especially layers, may be exaggerated in size for better illustration and / or understanding.

[0056] The semiconductor laser according to the embodiment of the Fig. 1 and Fig. 2 has a substrate 1 which, for example, comprises or consists of GaN. Furthermore, the semiconductor laser comprises an epitaxial semiconductor layer sequence 2 which is epitaxially oriented in a growth direction D. G grew on substrate 1.

[0057] The Fig. Figure 1 shows a top view of a facet 3 as well as details of the epitaxial semiconductor layer sequence 2 of the semiconductor laser, while the Fig. Figure 2 shows a simplified perspective view of the semiconductor laser. In particular, the Fig. 2 no bridge waveguide 4 and no details of the layers of the epitaxial semiconductor layer sequence 2 of the semiconductor laser.

[0058] The epitaxial semiconductor layer sequence 2 comprises a p-doped region 5, an n-doped region 6, and an active zone 7 located between the p-doped region 5 and the n-doped region 6. The active zone 7 includes quantum wells, particularly with pn junctions, for generating electromagnetic radiation during operation. Furthermore, the p-doped region 5 includes a waveguide 4 for guiding electromagnetic laser radiation 20 within an amplification region 8.

[0059] The amplification region 8 comprises a portion of the active zone 7. Within the amplification region 8, modes of the electromagnetic laser radiation 20 are amplified. In particular, the electromagnetic laser radiation 20 includes a fundamental mode that is to be amplified within the amplification region 8. The electromagnetic laser radiation 20 propagates within the amplification region 8 in a propagation direction D. P out, perpendicular to the growth direction D G is arranged.

[0060] The n-doped region 6 of the epitaxial semiconductor layer sequence 2 comprises an n-doped layer 9 that directly adjoins the active zone 7. The n-doped layer 9 of the epitaxial semiconductor layer sequence 2 has, for example, a thickness between 50 nanometers and 200 nanometers inclusive, and in particular a thickness between 50 nanometers and 100 nanometers inclusive.

[0061] Furthermore, an n-doped cladding layer 10 of the epitaxial semiconductor layer sequence 2 is arranged in direct contact with the n-doped layer 9. The n-doped cladding layer 10 comprises an n-(Al)GaN layer 11 and an n-GaN layer 12, wherein the n-GaN layer 12 is epitaxially grown by a low-temperature process.

[0062] The n-doped cladding layer 10 further comprises a mode-shifting layer 13, which shifts a mode of the electromagnetic laser radiation 20 such that it overlaps with the amplification region 8. In this case, the mode-shifting layer 13 is a mode-shifting layer stack 14, which comprises or consists of a single layer 15 comprising or consisting of AlInN and another single layer 15' comprising or consisting of (Al)GaN.

[0063] The mode-shifting layer 13, for example, has a thickness of at most 100 nanometers and includes vias 16 that completely penetrate the mode-shifting layer 13. In this case, the vias 16 are arranged laterally to the enhancement region 8, so that the mode-shifting layer 13 is continuous in a top view of the epitaxial semiconductor layer sequence 2 below the enhancement region 8. In other words, the mode-shifting layer 13 extends continuously along the enhancement region 8. The side faces 17 of the vias 16 are oriented with respect to the growth direction D. G inclined to the epitaxial semiconductor layer sequence 2.

[0064] It is also possible that the mode-shifting layer 13 is a superlattice made up of individual AlInN layers with different material compositions. In this case, the mode-shifting layer 13 has a thickness of no more than 50 nanometers, for example.

[0065] The n-doped region 6 further comprises a first n-(Al)GaN layer 18, which is deposited directly onto the substrate 1. The first n-(Al)GaN layer 18 acts as a cladding layer, leading to a thinner mode-shifting layer 13. The first n-(Al)GaN layer 18 has, for example, a thickness of no more than 3000 nanometers and preferably between 200 nanometers and 2000 nanometers.

[0066] The semiconductor laser of Fig. 1 and Fig. 2 is an edge-emitting semiconductor laser, in particular an edge-emitting semiconductor laser diode. In particular, the semiconductor laser comprises the Fig. 1 and Fig. 2 two oppositely arranged facets 3. The facets 3 limit the epitaxial semiconductor layer sequence 2 on their side surfaces and form an optical resonator 19 of the semiconductor laser. Fig. Figure 1 shows a top view of one of the facets.

[0067] In particular, electromagnetic laser radiation 20, which is generated within the amplification region 9, is emitted from the facet 3, especially from the amplification region 9 at the facet 3 (see Fig. 2).

[0068] The n-doped cladding layer 10 comprises, for example, the n-(Al)GaN layer 11 and has a thickness of at most 100 nanometers. Another semiconductor layer, deposited on the mode-shifting layer 13 and filling the vias 16 of the mode-shifting layer 13, is epitaxially grown by a low-temperature process and comprises, for example, n-GaN or consists of n-GaN. This n-GaN layer 12 has, for example, a thickness between 50 nanometers and 250 nanometers inclusive, and in particular between 50 nanometers and 150 nanometers. It is also possible that the n-GaN layer 12 additionally contains Al. The n-doped cladding layer 10 has, for example, a thickness between 50 nanometers and 500 nanometers inclusive.

[0069] An n-contact layer 21, which may, for example, comprise or consist of a metal, is deposited on an outer main surface of the substrate 1. The n-contact layer 21 completely covers the outer main surface of the substrate 1. It is also possible that the n-contact layer is structured. Furthermore, a p-contact layer 22, which may, for example, comprise or consist of a metal, is deposited on a front face of the waveguide 4. The p-contact layer 22 completely covers the front face of the waveguide 4.

[0070] During operation of the semiconductor laser, an electric current I flows between the n-contact layer 21 and the p-contact layer 22 through the active zone 7. Within the active zone 7, photons are generated from the electric charge carriers of the electric current I and amplified by stimulated emission within the optical resonator 19, so that electromagnetic laser radiation 20 is generated within the amplification region 8.

[0071] Since the vias 16 within the mode-shifting layer 13 are filled with a semiconductor material whose electrical resistance is lower than the electrical resistance of the mode-shifting layer 13, the electric current I flows particularly through the vias 15, thus improving the efficiency of the semiconductor laser.

[0072] Compared to the semiconductor laser of the Fig. 1 and Fig. 2 The semiconductor laser according to the exemplary embodiment of the Fig. 3 a second n-(Al)GaN layer 23 within the n-doped cladding layer 10 of the n-doped region 6. The mode-shifting layer 13 is arranged between the first n-(Al)GaN layer 18 and the second n-(Al)GaN layer 23. In particular, the first n-(Al)GaN layer 18 and the second n-(Al)GaN layer 23 extend completely along the facet 3 of the semiconductor laser and, in particular, cover the vias 16 within the mode-shifting layer 13, which can be seen in a top view on a first principal surface of the epitaxial semiconductor layer sequence 2.

[0073] In the present embodiment, the vias 16 of the mode-shifting layer 13 are connected to a surface of the epitaxial semiconductor layer sequence 2. In other words, the vias 16 do not have closed side faces 17. In particular, the mode-shifting layer 13 is arranged only below the gain region 8, while regions located laterally to the gain region 8 and, in particular, to the waveguide 4, are completely free of the mode-shifting layer 13. Specifically, an electric current I flows away from the mode-shifting layer 13 through the vias 16.

[0074] It is also possible that the mode-shifting layer 13 comprises a plurality of vias 16 within a region that, in a top view of the epitaxial semiconductor layer sequence 2, does not overlap with the gain region 8. For example, the vias 16 are arranged periodically.

[0075] Compared to the semiconductor laser of the Fig. 1 and Fig. 2 The semiconductor laser according to the exemplary embodiment of the Fig. 4 a photonic crystal layer 24 as a mode enhancement / mode selection element.

[0076] The photonic crystal layer 24 is formed by the p-doped region of the epitaxial semiconductor layer sequence. The p-doped region comprising the photonic crystal layer has, for example, a thickness of at least 100 nanometers, and in particular at least 300 nanometers.

[0077] The photonic crystal layer 24 selects modes of the electromagnetic laser radiation 20 that are generated within a gain range 8 during the operation of the semiconductor laser. In particular, the modes 25 of the electromagnetic laser radiation 20 propagate within the gain range 8 along a propagation direction D. P in the epitaxial semiconductor layer sequence 2.

[0078] The photonic crystal layer 24 comprises a multitude of structural elements, in this case holes 26, which are oriented along a growth direction D Gthe epitaxial semiconductor layer sequence 2. The holes 26 are arranged periodically within the photonic crystal layer 24. For example, the holes 26 are arranged at equal intervals from each other, or the distance between two directly adjacent holes 26 increases from a central region to an outer region of the epitaxial semiconductor layer sequence 2. Furthermore, the photonic crystal layer 24 deflects a portion of the electromagnetic laser radiation 20 to a radiation exit surface 27, which is part of an outer main surface of the substrate 2.

[0079] In particular, the p-doped region 5 of the epitaxial semiconductor layer sequence 2 is completely covered by a p-contact layer 22, which is in direct contact with the p-doped region 5. The radiation emission surface 27 of the substrate 1 opposite the p-contact layer 22 is, in particular, surrounded by an n-contact layer 21. The p-contact layer 22 and the n-contact layer 21 are, for example, formed from a metal.

[0080] In comparison to the semiconductor laser of the Fig. 4 The semiconductor laser according to the exemplary embodiment of the Fig. 5 a multitude of vias 16 within the mode-shifting layer 13. As shown in the top view of the p-doped region 5 of the epitaxial semiconductor layer sequence 2 in the upper part of Fig. As can be seen in Figure 5, the vias 16 are arranged periodically in a hexagonal lattice. Preferably, the arrangement of the vias 16 improves the functionality of the photonic crystal layer 24. It is also possible for the vias 16 to be arranged irregularly in order to suppress a systematic influence on the functionality of the photonic crystal layer 24.

[0081] In comparison to the semiconductor laser according to the embodiment of the Fig. 4. The semiconductor laser exhibits, according to the embodiment of the Fig. 6 a current distribution layer 28, which is arranged between the active zone 7 and the mode-shifting layer 13. In particular, the current distribution layer 28 is arranged directly adjacent to the n-doped cladding layer 10 and further directly adjacent to the n-doped layer 9 of the epitaxial semiconductor layer sequence 2. In particular, the current distribution layer 28 is configured to distribute a current flow homogeneously within the active zone 7. For example, the current distribution layer 28 is a superlattice of alternating (Al)GaN layers and GaN layers or alternating InGaN layers and GaN layers.

[0082] The semiconductor laser according to the embodiment of the Fig. 7 differs from the semiconductor laser of the Fig. 4 especially in the arrangement of the n-contact layer 21.

[0083] The semiconductor laser comprises a mesa 29 that exposes the n-doped region 5 of the epitaxial semiconductor layer sequence 2 below the mode-shifting layer 13 and surrounds a central region of the epitaxial semiconductor layer sequence 2. The mesa 29 is, for example, ring-shaped in a top view of the epitaxial semiconductor layer sequence 2. The n-contact layer 21 is arranged on the surface of the n-doped region 5 exposed by the mesa 29.

[0084] During the process for manufacturing a semiconductor laser according to the embodiment of the Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12 to Fig. 13 a growth substrate 1 is provided ( Fig. 8) The growth substrate 1 comprises or consists, for example, of gallium nitride. In particular, the growth substrate 1 has a growth surface 30, for example, a c-plane of the gallium nitride. The c-plane of the gallium nitride has, in particular, a lattice constant of 5.185.

[0085] An epitaxial semiconductor layer sequence 2 is, as in connection with the Fig. 9, Fig. 10, Fig. 11 to Fig. 12 described, grown epitaxially on the growth substrate 1.

[0086] On the growth area 30 of the growth substrate 1, a first n-(Al)GaN layer 18 is grown. As for example in Fig. As shown in Figure 9, an n-doped cladding layer 10 is epitaxially grown on the first n-(Al)GaN layer 18. The n-doped cladding layer 10 comprises a mode-shifting layer 13, which contains or consists of AlInN and has a thickness of at most 100 nanometers. The mode-shifting layer 13 can be doped or undoped. The material of the n-doped cladding layer 10, in which the mode-shifting layer 13 is embedded, is, for example, GaN.

[0087] It is also possible to deposit the n-doped mantle layer 10 directly epitaxially onto the growth surface 30 of the growth substrate 1 and to omit the first n-(Al)GaN layer 18.

[0088] For example, in Fig. As shown in Figure 10, a multitude of vias 16 are etched into the mode-shifting layer 13. The etching of the vias 16 ends within the GaN material of the n-cladding layer 10 between the mode-shifting layer 13 and the first n-(Al)GaN layer 18.

[0089] In particular, the mode-shifting layer 13 is lattice-matched to the lattice constant of the growth substrate 1 of approximately 5.185. Specifically, all materials of the epitaxial semiconductor layer sequence 2 are lattice-matched to at least reduce the stresses within the epitaxial semiconductor layer sequence 2.

[0090] In the next step, as for example in Fig. Figure 11 shows that an n-GaN layer 12, which is part of the n-doped cladding layer 10, is regrowth on the mode-shifting layer 13 using a low-temperature process. In particular, the n-GaN layer 12 completely fills the vias 16 and planarizes the surface of the mode-shifting layer 13. After the regrowth of the n-GaN layer 12 and before the deposition of an active zone 7, high-temperature defect healing and surface planarization can occur through enhanced ad atom diffusion at the surface.

[0091] In the next step, an n-doped layer 9 is grown epitaxially, followed by an active zone 7 and a p-doped region 5 ( Fig. 12).

[0092] Subsequently, a photonic crystal layer 24 is formed within the p-doped region 5, for example by creating holes 26 within the p-doped region 5. Furthermore, a p-contact layer 22 is applied to the p-doped region 5 and an n-contact layer 21 is applied to the growth substrate 1 ( Fig. 13) A semiconductor laser, such as those already used in connection with Fig. As explained in section 4, this is how it is achieved.

[0093] The present application claims priority over German application DE 102024101145.9, the disclosure of which is hereby incorporated by reference.

[0094] The invention is not limited to the description of exemplary embodiments. Rather, the invention encompasses any new feature as well as any combination of features, in particular any combination of features of the claims, even if the feature or combination of features itself is not expressly stated in the claims or the exemplary embodiments. Reference sign 1 substrate 2 epitaxial semiconductor layer sequence 3 facets 4 waveguides 5 p-doped area 6 n-doped area 7 active zones 8 Amplification range 9 n-doped layer 10 n-doped mantle layer 11 n-(Al)GaN layer 12 n-GaN layer 13 Mode shift layer 14 mode shift layer stacks 15 single shifts 15' further single shift 16 Through-hole plating 17 Side surface of the via 18 first n-(Al)GaN layer 19 optical resonator 20 electromagnetic laser radiation 21 n-contact layer 22 p-contact layer 23 second n-(Al)GaN layer 24 photonic crystal layers 25 Fashion 26 holes 27 Radiation emission surface 28 Power distribution layer 29 Mesa 30 growth area D G direction of growth D P Direction of spread I electric current QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102024101145.9

[0093]

Claims

Semiconductor laser comprising: - an epitaxial semiconductor layer sequence (2) based on a nitride compound semiconductor material, comprising a p-doped region (5) and an n-doped region (6) as well as an active zone (7) located between the p-doped region (5) and the n-doped region (6), and - a mode-shifting layer (13) located within or adjacent to the n-doped region (6), wherein - the mode-shifting layer (13) positions a mode (25) of the electromagnetic laser radiation (20) such that it overlaps with a gain region (8) of the epitaxial semiconductor layer sequence (2) during operation, the gain region (8) being configured to generate electromagnetic laser radiation (20) during operation, - the mode-shifting layer (13) has at least one via (16). Semiconductor laser according to the preceding claim, wherein- the n-doped region (6) comprises an n-doped cladding layer (10), and- the mode-shifting layer (13) is arranged within the n-doped cladding layer (10) or adjacent to the n-doped cladding layer (10). Semiconductor laser according to one of the preceding claims, wherein the mode-shifting layer (13) extends continuously along the gain region (9). Semiconductor laser according to one of the preceding claims, wherein the mode-shifting layer (13) comprises AlInN and / or AlGaN and / or AlInGaN. Semiconductor laser according to one of the preceding claims, wherein the mode-shifting layer (13) has an indium content between 16% inclusive and 19% inclusive. Semiconductor laser according to one of the preceding claims, wherein the mode-shifting layer (13) has a thickness of at most 200 nanometers. Semiconductor laser according to one of the preceding claims, wherein- the mode-shifting layer (13) is a mode-shifting layer stack (14) with two or more single layers (15, 15'), and- a single layer (15) of the mode-shifting layer stack (14) comprises AlInN and a single layer (15') of the mode-shifting layer stack (14) comprises (Al)GaN. Semiconductor laser according to one of the preceding claims, wherein the n-doped region (6) further comprises a first n-(Al)GaN layer (18) arranged between the mode-shifting layer (13) and a substrate (1) of the semiconductor laser. Semiconductor laser according to the preceding claim, wherein the n-doped region (6) further comprises a second n-(Al)GaN layer (23), and the mode-shifting layer (13) is arranged between the first n-(Al)GaN layer (18) and the second n-(Al)GaN layer (23). Semiconductor laser according to the preceding claim, wherein a current distribution layer (28) is arranged between the active zone (7) and the mode shifting layer (13). Semiconductor laser according to one of the preceding claims, wherein facets (3) delimit the epitaxial semiconductor layer sequence (2) on opposite side surfaces, wherein the facets (3) are arranged perpendicular to a propagation direction (DP) of the electromagnetic laser radiation (20) within the epitaxial semiconductor layer sequence (2). Semiconductor laser according to one of claims 1 to 10, further comprising a photonic crystal layer (24) which enhances and / or selects the modes of the electromagnetic laser radiation (20). Semiconductor laser according to the preceding claim, wherein - the photonic crystal layer (24) comprises periodically arranged structural elements, - the mode-shifting layer (13) comprises a plurality of periodically arranged vias (16), and - the periodicity of the vias (16) is at least a factor of 10 greater than the periodicity of the structural elements of the photonic crystal layer (24). A method for fabricating a semiconductor laser, comprising the following steps: - providing a substrate (1), - epitaxial growth of an epitaxial semiconductor layer sequence (2) based on a nitride compound semiconductor material on the growth substrate (1), wherein the epitaxial semiconductor layer sequence (2) comprises a p-doped region (5) and an n-doped region (6) as well as an active zone (7) located between the p-doped region (5) and the n-doped region (6), wherein - a mode-shifting layer (13) is located within or adjacent to the n-doped region (6), - the mode-shifting layer (13) positions a mode (25) of the electromagnetic laser radiation (20) such that, during operation, it overlaps with a gain region (8) of the epitaxial semiconductor layer sequence (2), wherein the gain region (8) is configured to generate electromagnetic laser radiation (20) during operation.- the mode-shifting layer (13) has at least one via (16). Method according to the preceding claim, wherein the at least one through-hole (16) is etched into the mode-shifting layer (13) after the epitaxial growth of the mode-shifting layer (13). Method according to one of claims 7 or 8, wherein an (Al)GaN layer (11) is epitaxially grown on the mode-shifting layer (13) with the at least one via (16). Method according to the preceding claim, wherein the (Al)GaN layer (11) is epitaxially regrown by a low-temperature process.

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