Semiconductor laser and method for manufacturing a semiconductor laser

Abstract

A semiconductor laser with the following features is provided: - an epitaxial semiconductor layer sequence (2) based on a nitride compound semiconductor material comprising a p-doped region (5) and a n-doped region (6) and an active zone (7) arranged between the p-doped region (5) and the n-doped region (6), and - a mode pusher layer (13) arranged within the n-doped region (6) or adjacent to the n-doped region (6), wherein - the mode pusher layer (13) locates a mode (25) of the electromagnetic laser radiation (20) to overlap with a gain region (8) of the epitaxial semiconductor layer sequence (2) during operation, the gain region (8) being configured for generation of electromagnetic laser radiation (20) during operation, - the mode pusher layer (13) has at least one via (16). Further, a method for manufacturing a semiconductor laser is provided.

Description

[0001] Description

[0002] SEMICONDUCTOR LASER AND METHOD FOR MANUFACTURING A SEMICONDUCTOR LASER

[0003] A semiconductor laser and a method for manufacturing a semiconductor laser are provided .

[0004] It is an obj ect of the present application to provide an improved semiconductor laser, particularly an improved edge emitting semiconductor laser and an improved photonic crystal surface emitting laser . Furthermore , an improved method for manufacturing a semiconductor laser is to be provided .

[0005] These obj ects are achieved with a semiconductor laser having the features of claim 1 and a method having the steps of claim 14 .

[0006] Improved embodiments and developments of the semiconductor laser and the method for manufacturing a semiconductor laser are given in the dependent claims . Particularly, the semiconductor laser is a semiconductor laser diode .

[0007] According to an embodiment , the semiconductor laser comprises an epitaxial semiconductor layer sequence based on a nitride compound semiconductor material . Nitride compound semiconductor materials are compound semiconductor materials containing nitrogen, such as the materials from the system InxAlyGai-x-yN with 0 < x < 1 , 0 < y < 1 and x+y < 1 . Particularly, AlGaN with x=0 , InGaN with y=0 and GaN with x=y=0 are nitride compound semiconductor materials . Further, (Al ) GaN indicates x=0 and 0 < y < 1 . In other words , in the nitride compound semiconductor material indicated with (Al ) GaN, no indium is contained and aluminum is optionally as a component . Particularly, the epitaxial semiconductor layer sequence comprises a plurality of epitaxially grown semiconductor layers stacked above each other in a growth direction . The growth direction is perpendicular to a main extension plane of the epitaxial semiconductor layer sequence . Particularly, the epitaxial semiconductor layer sequence has a first main surface and an opposite arranged second main surface , the first main surface and the second main surface running parallel to each other and to the main extension plane . Particularly, the first main surface and the second main surface are perpendicular to the growth direction .

[0008] According to an embodiment of the semiconductor laser, the epitaxial semiconductor layer sequence comprises a p-doped region and an n-doped region and an active zone arranged between the p-doped region and the n-doped region .

[0009] Particularly, the active zone is configured for generation of electromagnetic radiation during operation . The active zone comprises , for example , a pn-transition, a double hetero structure , a single quantum well structure or a multi quantum well structure for the generation of the electromagnetic radiation .

[0010] According to a further embodiment of the semiconductor laser, the semiconductor laser comprises a mode pusher layer arranged within the n-doped region or adj acent to the n-doped region . Particularly, the mode pusher layer is part of the epitaxial semiconductor layer sequence and epitaxially grown as the other epitaxial semiconductor layers of the epitaxial semiconductor layer sequence . Particularly, the mode pusher layer comprises or consists of a nitride compound semiconductor material .

[0011] According to a further embodiment of the semiconductor laser, the mode pusher layer locates a mode of the electromagnetic laser radiation to overlap with a gain region of the epitaxial semiconductor layer sequence during operation, the gain region being configured to generate electromagnetic laser radiation . Particularly, the gain region comprises at least a part of the active zone . Particularly, the mode of the electromagnetic laser radiation located by the mode pusher layer is a predetermined mode of the electromagnetic laser radiation .

[0012] The active zone is , particularly, configured to generate electromagnetic radiation from electrical current running through the active zone . Within the semiconductor laser, the active zone is at least partially configured as a laser active medium . Within the laser active medium, electromagnetic laser radiation is generated during operation due to enhancement and / or selection of predetermined modes of the electromagnetic laser radiation . Particularly, a propagation direction of the electromagnetic laser radiation within the epitaxial semiconductor layer sequence is perpendicular to the growth direction of the epitaxial semiconductor layer sequence .

[0013] For example , the semiconductor laser comprises an optical resonator for the enhancement and / or the selection of modes of the electromagnetic laser radiation, wherein the laser active medium, such as the active zone , is arranged . The active zone alone is configured to generate electromagnetic radiation by spontaneous emission . I f the active zone is arranged within the optical resonator, population inversion is achieved within the part of the active zone comprised by the gain region and electromagnetic laser radiation is generated by stimulated emission . Particularly, electromagnetic laser radiation generated by stimulated emission has a high coherence length, a small emission spectrum and a high polari zation degree compared to electromagnetic radiation generated by spontaneous emission .

[0014] A plurality of optical modes of the electromagnetic laser radiation being eigensolutions of the optical resonator is formed within the optical resonator during operation of the semiconductor laser . Particularly, a basic mode of electromagnetic laser radiation is formed within the optical resonator . Particularly, the semiconductor laser emits electromagnetic laser radiation of one single mode , particularly of the basic mode . For example , the electromagnetic laser radiation is blue and / or green electromagnetic laser radiation .

[0015] Further, it is possible that the semiconductor laser comprises a photonic crystal layer with a photonic crystal for the enhancement and / or the selections of modes of the electromagnetic laser radiation . Photonic crystals have a photonic band gap for photons equivalent to the electronic band gap of semiconductors for charge carriers . Photons with energies within the photonic band gap cannot propagate in the photonic crystal and are reflected by it . The photonic bandgap is formed, completely or partially, due to periodic structures of at least two materials of the photonic crystal . At present , the photonic crystal of the photonic crystal layer is , particularly, a two-dimensional photonic crystal , wherein the periodic structures are periodic in two spatial directions . The photonic crystal layer is arranged close to the active zone and particularly to the part of the active zone comprised by the gain region and leads to stimulated emission of electromagnetic laser radiation within the part of the active zone comprised by the gain region .

[0016] In particular, the mode pusher layer is configured to push a mode of the electromagnetic laser radiation, particularly the basic mode of the electromagnetic laser radiation, to overlap with the gain region . In other words , the mode of the electromagnetic laser radiation within the epitaxial semiconductor layer sequence without the mode pusher layer has a smaller overlap with the gain region than within an epitaxial semiconductor layer sequence having the mode pusher layer . The mode pusher layer particularly leads to a higher ef ficiency of the semiconductor laser . Particularly, the mode pusher layer has a lower refractive index than the surrounding semiconductor material , resulting in the mode of the electromagnetic laser radiation being pushed back to overlap with the gain region . Particularly, the mode pusher layer is intentionally undoped or n-doped .

[0017] According to a further embodiment of the semiconductor laser, the mode pusher layer has at least one via . Particularly, the via is configured for the passage of electrical current through the mode pusher layer . Particularly, the at least one via penetrates the mode pusher layer completely . For example , the via is filled with semiconductor material of the epitaxial semiconductor layer sequence . For example , a diameter of the at least one via does not exceed 10 micrometer or does not exceed 2 micrometer . Particularly, it is not mandatory that a side face of the via is completely closed . For example , a volume of the via closes up is freely accessible at a side surface of the epitaxial semiconductor layer sequence .

[0018] According to a further embodiment of the semiconductor laser, the mode pusher layer comprises a plurality of vias . For example , the vias are embodied equally or di f ferently from each other . For example , the vias are randomly distributed within the mode pusher layer or in an ordered manner . For example , two directly adj acent vias have the same distances to each other or the distance between two directly adj acent vias varies over the mode pusher layer . For example , the distance between two directly adj acent vias is larger in an outer region of the mode pusher layer and becomes continuously smaller from the outer region to a central region of the mode pusher layer . For example , the at least one via has a side face tilted or perpendicular with respect to the growth direction of the epitaxial semiconductor layer sequence .

[0019] According to a further embodiment , the semiconductor laser comprises :

[0020] - 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 arranged between the p-doped region and the n-doped region, and

[0021] - the mode pusher layer arranged within the n-doped region or adj acent to the n-doped region, wherein

[0022] - the mode pusher layer locates the mode of the electromagnetic laser radiation to overlap with the gain region of the epitaxial semiconductor layer sequence during operation, and the mode pusher layer has the at least one via .

[0023] At present , the epitaxial semiconductor layer sequence is provided with the mode pusher layer for relocation of the predetermined mode of the electromagnetic laser radiation to overlap with the gain region to improve ef ficiency of the semiconductor laser .

[0024] Often, a material of the mode pusher layer, which is suitable for relocating the mode of the electromagnetic laser radiation in the desired manner, leads simulteously to an enhanced voltage drop accros the epitaxial semicondcutor layer sequence . The semiconductor laser is inter alia based on the idea to provide the mode pusher layer with the at least one via allowing an enhanced flow of electrical current through the via for reducing the voltage drop . Particularly, the via is filled with a semiconductor material having an enhanced electrical conductivity compared to the material of the mode pusher layer . For example , the material of the mode pusher layer is undoped, while the material filled in the via is doped, particularly n-doped . The mode pusher layer with the via particularly provide a reduced electrical resistance of the semiconductor laser .

[0025] According to an embodiment of the semiconductor laser, the n- doped region comprises an n-doped cladding layer and the mode pusher layer is arranged within the n-doped cladding layer or adj acent , particularly directly adj acent , to the n-doped cladding layer . For example , the mode pusher layer is in direct contact with the n-doped cladding layer and has a common interface with the n-doped cladding layer . For example , the n-doped cladding layer comprises or consists of n-doped GaN or n-doped AlGaN . Particularly, the n-doped cladding layer has a refractive index larger than the refractive index of the mode pusher layer and smaller than the refractive index of the active zone . For example , the n- doped cladding layer has a thickness between and including 500 nanometer to 3 micrometer . Particularly, the n-doped cladding layer suppresses propagation of modes of the electromagnetic laser radiation in a substrate of the semiconductor laser, particularly in a growth substrate of the epitaxial semiconductor layer sequence . The mode pusher layer allows a thickness of the n-doped cladding layer to be reduced such that the epitaxial semiconductor layer sequence has reduced stress , in particular .

[0026] According to a further embodiment of the semiconductor laser, the mode pusher layer extends continuously along the gain region . In other words , seen in plan view on the epitaxial semiconductor layer sequence the one or more vias within the mode pusher layer are arranged laterally to the gain region . A region of the mode pusher layer along the gain region is free of vias . Particularly, the region of the mode pusher layer arranged below the gain region seen in plan view on the gain region is free of vias . In the case of an edge emitting laser having a ridge wave guide , the region below the ridge wave guide seen in plan view on the ridge wave guide is free of vias , for example . This has the advantage that the mode of the electromagnetic laser radiation is particularly ef ficiently relocated to overlap with the gain region, while flow of electrical current through the active zone is enhanced simultaneously .

[0027] According to a further embodiment of the semiconductor laser, the mode pusher layer comprises or consists of Al lnN and / or AlGaN and / or Al InGaN . Particularly preferably, the mode pusher layer comprises or consists of Al lnN . For example , the mode pusher layer is not intentionally doped or n-doped . For example , the mode pusher layer has a refractive index of at most 2 . 35 or at most 2 . 30 . It is also possible that the refractive index is slightly higher .

[0028] According to a further embodiment of the semiconductor laser, the mode pusher layer has an indium content between and including 15% and 20% , preferred between 16% and 19% , especially preferred between 17 % and 18 % . Particularly, the mode pusher layer comprises or consists of Al lnN and has an indium content between and including 16% and 19% . Particularly, the semiconductor material of the mode pusher layer is lattice-matched to the surrounding semiconductor material . This is particularly achieved with an indium content between and including 16% and 19% and particularly of about 18 % .

[0029] According to a further embodiment of the semiconductor laser, the mode pusher layer has a thickness of at most 100 nanometer or of at most 200 nanometer or of at most 500 nanometer . It is advantageous to use a mode pusher layer having a very small thickness , since then the voltage drop across the epitaxial semiconductor layer sequence is reduced .

[0030] According to a further embodiment of the semiconductor laser, the mode pusher layer is a mode pusher layer stack with two or more single layers . In other words , the mode pusher layer comprises two or more single layers being di f ferent in their material composition . For example , a single layer of the mode pusher layer stack comprises Al lnN and a further single layer of the mode pusher layer stack comprises (Al ) GaN . In other words , one single layer of the mode pusher layer stack comprises a nitride semiconductor compound material with indium, while the further single layer of the mode pusher layer stack is free of indium .

[0031] According to a further embodiment of the semiconductor laser, the n-doped region further comprises a first n- (Al ) GaN layer arranged between the mode pusher layer and the substrate of the semiconductor laser . Particularly, 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 directly applied to the substrate . Particularly, the first n- (Al ) GaN layer is epitaxially grown on a growth surface of the growth substrate . I f the first n- (Al ) GaN layer is provided within the epitaxial semiconductor layer sequence , the mode pusher layer can be reduced in thickness advantageously .

[0032] According to an embodiment of the semiconductor laser, the n- doped region further comprises a second n- (Al ) GaN layer and the mode pusher layer is arranged between the first n- (A1 ) GaN-layer and the second n- (Al ) GaN-layer . In other words , the mode pusher layer is sandwiched between both n- (Al ) GaN- layers . This arrangement particularly leads to an improved relocation of the mode of the electromagnetic laser radiation .

[0033] According to a further embodiment of the semiconductor laser, a current spreading layer is arranged between the active zone and the mode pusher layer . Particularly, the current spreading layer is configured to spread an electrical current within the epitaxial semiconductor layer sequence and particularly within the active zone . Preferably, the current spreading layer extends continuously within the epitaxial semiconductor layer sequence along their main extension plane . For example , the current spreading layer comprises or consists of InGaN, AlGaN or GaN . For example , the current spreading layer comprises or consists of a superlattice of alternatingly arranged layers . For example , the superlattice comprises or consists of alternatingly arranged (Al ) GaN- layers and GaN layers or of alternatingly arranged InGaN layers and GaN layers .

[0034] According to a further embodiment of the semiconductor laser, facets limit the epitaxial semiconductor layer sequence at opposite arranged side faces , the facets being arranged perpendicular to the propagation direction of the electromagnetic laser radiation within the epitaxial semiconductor layer sequence .

[0035] Particularly, the facets form the optical resonator of the semiconductor laser . The active zone is arranged within the optical resonator as a laser active medium and population inversion is achieved within the part of the active region comprised by the gain region during operation of the semiconductor laser . The electromagnetic laser radiation generated within the gain region by stimulated emission propagates between the facets of the semiconductor laser in the propagation direction .

[0036] Particularly, one of the facets is provided with a high reflective layer being highly reflective for the electromagnetic laser radiation, while the other facet is provided with a partially transparent layer being partially transparent for the electromagnetic laser radiation such that electromagnetic laser radiation is coupled out from that facet during operation . In this embodiment the semiconductor laser is , in other words , an edge emitting semiconductor laser .

[0037] According to a further embodiment , the semiconductor laser comprises a photonic crystal layer enhancing and / or selecting modes of the electromagnetic laser radiation . Particularly, the photonic crystal layer comprises or consists of a two- dimensional photonic crystal . In this embodiment , the semiconductor laser particularly does not comprise facets forming the optical resonator for mode enhancement and / or mode selection, but a photonic crystal layer with a photonic crystal for mode enhancement and / or mode selection . The photonic crystal layer particularly enhances and / or selects modes of the electromagnetic laser radiation propagating along the propagation direction being perpendicular to a growth direction of the epitaxial semiconductor layer sequence . Particularly, the propagation direction of the electromagnetic laser radiation is perpendicular to side faces of the epitaxial semiconductor layer sequence as in the edge emitting semiconductor laser .

[0038] Further, the photonic crystal redirects particularly a part of the electromagnetic laser radiation propagating within the gain region to a radiation exit surface of the semiconductor laser being particularly part of a first main surface or a second main surface of the semiconductor laser .

[0039] The semiconductor laser with the photonic crystal layer for enhancing and / or selecting modes of the electromagnetic laser radiation is particularly a photonic cavity surface emitting semiconductor laser ( short : "PCSEL" ) . Particularly, the photonic crystal layer is part of the p- doped region of the epitaxial semiconductor layer sequence . The mode pusher layer particularly locates the mode of the electromagnetic laser radiation to overlap not only with the gain region of the epitaxial semiconductor layer sequence , but also with the photonic crystal layer of the PCSEL .

[0040] The photonic crystal layer particularly runs 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 epitaxially grown . For example , the photonic crystal layer is manufactured from an epitaxially grown semiconductor layer which is provided with periodically arranged structure elements , such as holes , after epitaxial growth . For example , the holes extend along the growth direction of the epitaxial semiconductor layer sequence and being arranged within the p-region at a periodic distance . The holes might be filled with a further material , for example a dielectric material . The holes and / or the material within the holes particularly have a high di f ference in refractive index compared to the surrounding semiconductor material of the p-doped region .

[0041] According to an embodiment of the semiconductor laser, the photonic crystal layer comprises periodically arranged structure elements and a plurality of vias within the mode pusher layer being also periodically arranged . Particularly, a periodicity of the vias is larger by at least a factor 10 than a periodicity of the structure elements of the photonic crystal layer . Particularly, the substrate is provided with an n-contact layer, for example comprising or consisting of a metal . I f the semiconductor laser is an edge emitting semiconductor laser, a further p-contact is particularly arranged on or over the p-doped region, making electrical contact to the p- doped region . In such a way, electrical current flows along the growth direction through the epitaxial semiconductor layer sequence during operation .

[0042] According to an embodiment , the semiconductor laser embodied as an edge emitting semiconductor laser comprises a ridge waveguide etched within the epitaxial semiconductor layer sequence , particularly within the p-doped region of the epitaxial semiconductor layer sequence . The gain region particularly overlaps with the ridge waveguide seen in plan view on the epitaxial semiconductor layer sequence , preferably completely . Particularly, the p-contact layer is arranged on the ridge waveguide .

[0043] According to an embodiment , the p-contact layer is , for example , arranged on or over the photonic crystal layer, and covers the photonic crystal layer particularly completely . For example , the p-contact layer is embodied as a mirror for the electromagnetic laser radiation . The p-contact layer may comprise or consist of a metal .

[0044] In the case that the semiconductor laser is embodied as a PCSEL and comprises a photonic crystal layer for mode selection and / or mode enhancement , the n-contact layer is , for example , arranged in an outer region of the substrate surrounding a centrally arranged radiation exit surface of the substrate . It is also possible that the photonic crystal layer comprises a mesa penetrating the p-doped region and the active zone such that access is provided to the n-doped region of the epitaxial semiconductor layer sequence . In that case , the n-contact layer is arranged within the vias on the n-doped region for electrical contact , particularly .

[0045] For example , the semiconductor laser finds application in augmented reality (AR) / virtual reality (VR) devices such as AR / VR glasses . Further, the semiconductor laser can be used as a high power laser for proj ection and material processing .

[0046] The semiconductor laser described herein can be manufactured with the method disclosed in the following . Therefore , features and embodiments disclosed in connection with the semiconductor laser can also be embodied within the method and vice versa .

[0047] According to an embodiment of the method for manufacturing a semiconductor laser, a substrate is provided . Particularly, the substrate is a growth substrate and configured for epitaxial growth of an epitaxial semiconductor layer sequence . Particularly, 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 surface configured for epitaxial growth of the epitaxial semiconductor layer sequence . For example , the growth surface is a c-plane of the growth substrate .

[0048] 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 . Particularly, the epitaxial semiconductor layer sequence comprises a p-doped region and an n-doped region and an active zone arranged between the p-doped region and the n- doped region . Particularly, the active zone is configured for generation of electromagnetic radiation by spontaneous emission .

[0049] According to a further embodiment of the method, a mode pusher layer is arranged within the n-doped region or adj acent to the n-doped region . Particularly, the mode pusher layer is part of the epitaxial semiconductor layer sequence and therefore also epitaxially grown on the growth substrate .

[0050] According to a further embodiment of the method, the mode pusher layer locates a mode of the electromagnetic laser radiation to overlap with a gain region of the epitaxial semiconductor layer sequence during operation . Particularly, the mode pusher layer has at least one via .

[0051] According to a preferred embodiment , the method for manufacturing the semiconductor laser comprises the steps :

[0052] - providing the substrate

[0053] - epitaxially growing the epitaxial semiconductor layer sequence based on the nitride compound semiconductor material on the growth substrate , the epitaxial semiconductor layer sequence comprising the p-doped region and the n-doped region and the active zone arranged between the p-doped region and the n-doped region, wherein

[0054] - the mode pusher layer is arranged within the n-doped region or adj acent to the n-doped region,

[0055] - the mode pusher layer locates the mode of the electromagnetic laser radiation to overlap with the gain region of the epitaxial semiconductor layer sequence during operation,

[0056] - the mode pusher layer has the at least one via, particularly for passage of the electrical current .

[0057] Particularly, these steps are carried out in the given order .

[0058] According to a further embodiment of the method, the at least one via is etched in the mode pusher layer after epitaxial growth of the mode pusher layer . In other words , the mode pusher layer is first epitaxially grown and particularly covers the growth substrate completely and then the at least one via is etched after the epitaxial growth of the mode pusher layer . Etching of the mode pusher layer in order to achieve the vias is , for example , carried out by dry chemical etching .

[0059] According to a further embodiment of the method, an (Al ) GaN- layer is epitaxially regrown on the mode pusher layer with the at least one via . In other words , after arranging the vias within the mode pusher layer, the (Al ) GaN-layer is epitaxially regrown on the mode pusher layer . During regrowth of the (Al ) GaN-layer on the mode pusher layer, the material of the (Al ) GaN-layer fills the vias , preferably completely . For example , the (Al ) GaN-layer has a thickness above the mode pusher layer between and including 50 nanometer to 250 nanometer and further, for example , between 50 nanometer and 150 nanometer .

[0060] According to a further embodiment of the method, the (Al ) GaN- layer is epitaxially regrown by a low temperature process . Particularly, the epitaxial regrowth of the (Al ) GaN-layer is performed during an epitaxial process having a temperature not exceeding 950 ° C, preferred not exceeding 900 ° C .

[0061] 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 connection with the Figures .

[0062] Figures 1 to 7 show schematic views of a semiconductor laser according to several exemplary embodiments .

[0063] Figures 8 to 13 show schematically sectional views of stages of a method for manufacturing a semiconductor laser according to an exemplary embodiment .

[0064] Equal or similar elements as well as elements of equal function are designated with the same reference signs in the Figures . The Figures and the proportions of the elements shown in the Figures are not regarded as being shown to scale . Rather, single elements , in particular layers , can be shown exaggerated in magnitude for the sake of better presentation and / or better understanding .

[0065] The semiconductor laser according to the exemplary embodiment of Figures 1 and 2 has a substrate 1 , for example comprising or consisting of a GaN . Further, the semiconductor laser comprises an epitaxial semiconductor layer sequence 2 epitaxially grown in a growth direction DGon the substrate 1 .

[0066] Figure 1 shows a plan view on one facet 3 as well as details of the epitaxial semiconductor layer sequence 2 of the semiconductor laser, while Figure 2 shows a simpli fied perspective view of the semiconductor laser . Particularly, Figure 2 does not show a ridge waveguide 4 and details of the layers of the epitaxial semiconductor layer sequence 2 of the semiconductor laser .

[0067] The epitaxial semiconductor layer sequence 2 comprises a p- doped region 5 and an n-doped region 6 and an active zone 7 arranged between the p-doped region 5 and the n-doped region 6 . The active zone 7 comprises quantum wells , particularly with pn j unctions , for the generation of electromagnetic radiation during operation . Further, the p-doped region 5 comprises a ridge waveguide 4 for guiding electromagnetic laser radiation 20 within a gain region 8 .

[0068] The gain region 8 comprises a part of the active zone 7 . Within the gain region 8 , ampli fication of modes of the electromagnetic laser radiation 20 takes place . Particularly, the electromagnetic laser radiation 20 comprises a basic mode which is to be ampli fied within the gain region 8 . The electromagnetic laser radiation 20 propagates within the gain region 8 in a propagation direction DPbeing arranged perpendicular to the growth direction DG.

[0069] The n-doped region 6 of the epitaxial semiconductor layer sequence 2 comprises at present an n-doped layer 9 directly adj acent to the active zone 7 . The n-doped layer 9 of the epitaxial semiconductor layer sequence 2 has , for example , a thickness between and including 50 nanometer to 200 nanometer and, particularly, a thickness between and including 50 nanometer and 100 nanometer .

[0070] Further, 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 a n- (Al ) GaN-layer 11 and an n-GaN layer 12 , the n- GaN layer 12 being epitaxially grown by a low temperature process .

[0071] The n-doped cladding layer 10 further comprises a mode pusher layer 13 relocating a mode of the electromagnetic laser radiation 20 to overlap with the gain region 8 . At present , the mode pusher layer 13 is a mode pusher layer stack 14 comprising a single layer 15 comprising or consisting of Al lnN and a further single layer 15 ' comprising or consisting of (Al ) GaN .

[0072] The mode pusher layer 13 has , for example , a thickness of at most 100 nanometer and comprises vias 16 completely penetrating the mode pusher layer 13 . At present , the vias 16 are arranged laterally to the gain region 8 so that the mode pusher layer 13 is continuously formed below the gain region 8 in plan view on the epitaxial semiconductor layer sequence 2 . In other words , the mode pusher layer 13 extends completely along the gain region 8 . Side faces 17 of the vias 16 are at present tilted with respect to the growth direction DGof the epitaxial semiconductor layer sequence 2 .

[0073] It is also possible , that the mode pusher layer 13 is a superlattice of individual Al lnN layers having di f ferent material compositions . In this case , the mode pusher layer 13 has , for example , a thickness not exceeding 50 nanometer .

[0074] The n-doped region 6 further comprises a first n- (Al ) GaN- layer 18 directly applied to the substrate 1 . The first n- (A1 ) GaN-layer 18 acts as a cladding layer leading to a thinner mode pusher layer 13 . The first n- (Al ) GaN-layer 18 has , for example , a thickness not exceeding 3000 nanometer and, preferably, between and including 200 nanometer and 2000 nanometer .

[0075] The semiconductor laser of Figures 1 and 2 is an edge emitting semiconductor laser, particularly an edge emitting semiconductor laser diode . Particularly, the semiconductor laser of Figures 1 and 2 comprises two facets 3 oppositely arranged to each other . The facets 3 limit the epitaxial semiconductor layer sequence 2 at their side faces and form an optical resonator 19 of the semiconductor laser . Figure 1 shows a plan view on one of the facets .

[0076] Particularly, electromagnetic laser radiation 20 generated within the gain region 9 is emitted from the facet 3 , particularly from the gain region 9 at the facet 3 ( see Figure 2 ) .

[0077] The n-doped cladding layer 10 particularly comprises the n- (Al ) GaN layer 11 for example , and having a thickness not exceeding 100 nanometer . A further semiconductor layer applied to the mode pusher layer 13 and filling the vias 16 of the mode pusher layer 13 is epitaxially regrown by a low temperature process and comprises n-GaN or consists of n-GaN, for example . This n-GaN layer 12 has , for example , a thickness between and including 50 nanometer to 250 nanometer, particularly 50 nanometer to 150 nanometer . It is also possible that the n-GaN layer 12 comprises additionally Al . The n-doped cladding layer 10 has , for example , a thickness between and including 50 nanometer and 500 nanometer . On an outer main surface of the substrate 1 , an n-contact layer 21 is applied, for example comprising or consisting of a metal . The n-contact layer 21 covers the outer main surface of the substrate 1 completely, for example . It is also possible that the n-contact layer is structured . Further, on a front face of the ridge waveguide 4 , a p-contact layer 22 is applied, for example comprising or consisting of a metal . The p-contact layer 22 covers the front face of the ridge waveguide 4 completely .

[0078] During operation of the semiconductor laser, an electrical 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 electrical charge carriers of the electrical current I and ampli fied by stimulated emission within the optical resonator 19 such that electromagnetic laser radiation 20 is generated within the gain region 8 .

[0079] Due to the vias 16 within the mode pusher layer 13 being filled with a semiconductor material with a lower electrical resistance than the electrical resistance of the mode pusher layer 13 , the electrical current I flows particularly through the vias 15 such that the ef ficiency of the semiconductor laser is enhanced .

[0080] Compared to the semiconductor laser of Figures 1 and 2 , the semiconductor laser according to the exemplary embodiment of Figure 3 comprises a second n- (Al ) GaN-layer 23 within the n- doped cladding layer 10 of the n-doped region 6 . The mode pusher layer 13 is sandwiched between the first n- (Al ) GaN- layer 18 and the second n- (Al ) GaN-layer 23 . Particularly, the first n- (Al ) GaN-layer 18 and the second n- (Al ) GaN-layer 23 completely extend along the facet 3 of the semiconductor laser and particularly cover the vias 16 within the mode pusher layer 13 seen in plan view on a first main surface of the epitaxial semiconductor layer sequence 2 .

[0081] In the present exemplary embodiment , the vias 16 of the mode pusher layer 13 close up with a surface of the epitaxial semiconductor layer sequence 2 . In other words , the vias 16 do not have closed side faces 17 . Particularly, the mode pusher layer 13 is only arranged below the gain region 8 while regions laterally arranged to the gain region 8 , and particularly to the ridge waveguide 4 , are completely free of the mode pusher layer 13 . Particularly, an electrical current I flows aside from the mode pusher layer 13 through the vias 16 .

[0082] It is also possible that the mode pusher layer 13 comprises a plurality of vias 16 within a region not overlapping with the gain region 8 seen in plan view on the epitaxial semiconductor layer sequence 2 . For example , the vias 16 are arranged periodically .

[0083] Compared to the semiconductor laser of Figures 1 and 2 , the semiconductor laser according to the exemplary embodiment of Figure 4 comprises a photonic crystal layer 24 as mode enhancing / mode selecting element .

[0084] The photonic crystal layer 24 is comprised by the p-doped region of the epitaxial semiconductor layer sequence . The p- doped region including the photonic crystal layer has , for example , a thickness of at least 100 nanometer, particularly of at least 300 nanometer . The photonic crystal layer 24 selects modes of the electromagnetic laser radiation 20 generated within a gain region 8 during operation of the semiconductor laser . Particularly, the modes 25 of the electromagnetic laser radiation 20 propagate within the gain region 8 along a propagation direction DPin the epitaxial semiconductor layer sequence 2 .

[0085] The photonic crystal layer 24 comprises a plurality of structure elements , at present holes 26 , extending along a growth direction DGof the epitaxial semiconductor layer sequence 2 . The holes 26 are arranged periodically within the photonic crystal layer 24 . For example , the holes 26 are equidistantly arranged from each other or the distance between two directly adj acent holes 26 becomes larger from a central region to an outer region of the epitaxial semiconductor layer sequence 2 . Further, the photonic crystal layer 24 redirects a part of the electromagnetic laser radiation 20 to a radiation exit surface 27 being part of an outer main surface of the substrate 2 .

[0086] Particularly, the p-doped region 5 of the epitaxial semiconductor layer sequence 2 is completely covered by a p- contact layer 22 being in direct contact with the p-doped region 5 . The radiation exit surface 27 of the substrate 1 opposite to the p-contact layer 22 is particularly surrounded by an n-contact layer 21 . The p-contact layer 22 as well as the n-contact layer 21 are , for example , formed by a metal .

[0087] Compared to the semiconductor laser of Figure 4 , the semiconductor laser according to the exemplary embodiment of Figure 5 comprises a plurality of vias 16 within the mode pusher layer 13 . As can be seen in the plan view on the p- doped region 5 of the epitaxial semiconductor layer sequence 2 shown in the upper part of Figure 5 , the vias 16 are arranged periodically in a hexagonal grid . Preferably, the arrangement of the vias 16 enhances the functionality of the photonic crystal layer 24 . It is also possible that the vias 16 are arranged in an irregular fashion in order to suppress a systematic impact on the functionality of the photonic crystal layer 24 .

[0088] Compared to the semiconductor laser according to the exemplary embodiment of Figure 4 , the semiconductor laser according to the exemplary embodiment of Figure 6 comprises a current spreading layer 28 arranged between the active zone 7 and the mode pusher layer 13 . Particularly, the current spreading layer 28 is arranged directly adj acent to the n- doped cladding layer 10 and further directly adj acent to the n-doped layer 9 of the epitaxial semiconductor layer sequence 2 . Particularly, the current spreading layer 28 is configured to distribute a current flow homogeneously within the active zone 7 . For example , the current spreading layer 28 is a superlattice of alternating (Al ) GaN-layers and GaN layers or of alternating InGaN layers and GaN layers .

[0089] The semiconductor laser according to the exemplary embodiment of Figure 7 di f fers from the semiconductor laser of Figure 4 particularly in the arrangement of the n-contact layer 21 .

[0090] The semiconductor laser comprises a mesa 29 exposing the n- doped region 5 of the epitaxial semiconductor layer sequence 2 below the mode pusher layer 13 and surrounding a central region of the epitaxial semiconductor layer sequence 2 . The mesa 29 is , for example , ring-shaped seen in plan view on the epitaxial semiconductor layer sequence 2 . On the surface of the n-doped region 5 exposed by the mesa 29 , the n-contact layer 21 is arranged .

[0091] During the method for manufacturing a semiconductor laser according to the exemplary embodiment of Figures 8 to 13 a growth substrate 1 is provided ( Figure 8 ) . For example , the growth substrate 1 comprises or consists of gallium nitride . Particularly, 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 , particularly, a lattice constant of 5 . 185 .

[0092] An epitaxial semiconductor layer sequence 2 is epitaxially grown on the growth substrate 1 as described in connection with Figures 9 to 12 .

[0093] On the growth surface 30 of the growth substrate 1 a first n- (A1 ) GaN-layer 18 is grown at present . As for example 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 pusher layer 13 comprising or consisting of Al lnN and having a thickness of at most 100 nanometer . The mode pusher layer 13 can be doped or undoped . The material of the n-doped cladding layer 10 embedding the mode pusher layer 13 is , for example , GaN .

[0094] It is also possible to directly epitaxially grow the n-doped cladding layer 10 on the growth surface 30 of the growth substrate 1 and to omit the first n- (Al ) GaN-layer 18 .

[0095] As for example shown in Figure 10 , a plurality of vias 16 is etched within the mode pusher layer 13 . The etching of the vias 16 stops within the GaN material of the n-cladding layer 10 between the mode pusher layer 13 and the first n- (Al ) GaN- layer 18 .

[0096] Particularly, the mode pusher layer 13 is lattice-matched with the lattice constant of the growth substrate 1 of about 5 . 185 . Particularly, all materials of the epitaxial semiconductor layer sequence 2 are lattice-matched for at least reducing stress within the epitaxial semiconductor layer sequence 2 .

[0097] In a next step, as for example shown in Figure 11 , an n-GaN layer 12 being part of the n-doped cladding layer 10 is regrown on the mode pusher layer 13 using a low temperature process . Particularly, the n-GaN layer 12 fills the vias 16 completely and planari zes the surface of the mode pusher layer 13 . After the regrowth of the n-GaN layer 12 and before application of an active zone 7 , high temperature defect healing and surface planari zation might take place by enhanced ad-atom di f fusion on the surface .

[0098] In a next step, an n-doped layer 9 is epitaxially grown, followed by an active zone 7 and a p-doped region 5 ( Figure

[0099] 12 ) .

[0100] Then 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 . Further, a p-contact layer 22 is applied on the p- doped region 5 as well as an n-contact layer 21 on the growth substrate 1 ( Figure 13 ) . A semiconductor laser is achieved as for example already explained in connection with Figure 4 . The present application claims priority of the German application DE 102024101145 . 9 , the disclosure content of which is incorporated herein by references . The invention is not limited to the description of the exemplary embodiments . Rather, the invention comprises each new feature as well as each combination of features , particularly each combination of features of the claims , even i f the feature or the combination of features itsel f is not explicitly given in the claims or the exemplary embodiments .

[0101] References

[0102] 1 substrate

[0103] 2 epitaxial semiconductor layer sequence

[0104] 3 facet

[0105] 4 ridge waveguide

[0106] 5 p-doped region

[0107] 6 n-doped region

[0108] 7 active zone

[0109] 8 gain region

[0110] 9 n-doped layer

[0111] 10 n-doped cladding layer

[0112] 11 n- (Al ) GaN-layer

[0113] 12 n-GaN layer

[0114] 13 mode pusher layer

[0115] 14 mode pusher layer stack

[0116] 15 single layer

[0117] 15 ' further single layer

[0118] 16 via

[0119] 17 side face of the via

[0120] 18 first n- (Al ) GaN-layer

[0121] 19 optical resonator

[0122] 20 electromagnetic laser radiation

[0123] 21 n-contact layer

[0124] 22 p-contact layer

[0125] 23 second n- (Al ) GaN-layer

[0126] 24 photonic crystal layer

[0127] 25 mode

[0128] 26 hole

[0129] 27 radiation exit surface

[0130] 28 current spreading layer

[0131] 29 mesa

[0132] 30 growth surface

[0133] DGgrowth direction

[0134] DPpropagation direction

[0135] I electrical current

Claims

Claims :

1. Semiconductor laser comprising:- an epitaxial semiconductor layer sequence (2) based on a nitride compound semiconductor material comprising a p-doped region (5) and a n-doped region (6) and an active zone (7) arranged between the p-doped region (5) and the n-doped region ( 6 ) , and- a mode pusher layer (13) arranged within the n-doped region (6) or adjacent to the n-doped region (6) , wherein- the mode pusher layer (13) locates a mode (25) of the electromagnetic laser radiation (20) to overlap with a gain region (8) of the epitaxial semiconductor layer sequence (2) during operation, the gain region (8) being configured for generation of electromagnetic laser radiation (20) during operation,- the mode pusher layer (13) has at least one via (16) .

2. Semiconductor laser according to the previous claim, wherein- the n-doped region (6) comprises a n-doped cladding layer (10) , and- the mode pusher layer (13) is arranged within the n-doped cladding layer (10) or adjacent to the n-doped cladding layer (10) .

3. Semiconductor laser according to any of the previous claims, wherein the mode pusher layer (13) extends continuously along the gain region ( 9 ) .

4. Semiconductor laser according to any of the previous claims, wherein the mode pusher layer (13) comprises AllnN and / or AlGaN and / or AlInGaN.

5. Semiconductor laser according to any of the previous claims, wherein the mode pusher layer (13) has an Indium content between and including 16% and 19%.

6. Semiconductor laser according to any of the previous claims, wherein the mode pusher layer (13) has a thickness of at most 200 nanometers .

7. Semiconductor laser according to any of the previous claims, wherein- the mode pusher layer (13) is a mode pusher layer stack(14) with two or more single layers (15, 15' ) , and- a single layer (15) of the mode pusher layer stack (14) comprises AllnN and a single layer (15' ) of the mode pusher layer stack (14) comprises (Al)GaN.

8. Semiconductor laser according to any of the previous claims, wherein the n-doped region (6) further comprises a first n- (Al)GaN layer (18) arranged between the mode pusher layer (13) and a substrate (1) of the semiconductor laser.

9. Semiconductor laser according to the previous claim, wherein- the n-doped region (6) further comprises a second n- (Al)GaN layer (23) , and- the mode pusher layer (13) is arranged between the first n- (Al)GaN layer (18) and the second n- (Al)GaN layer (23) .

10. Semiconductor laser according to the previous claim, wherein a current spreading layer (28) is arranged between the active zone (7) and the mode pusher layer (13) .

11. Semiconductor laser according to any of the previous claims, wherein facets (3) limit the epitaxial semiconductor layer sequence (2) at opposite arranged side faces, the facets (3) being arranged perpendicular to a propagation direction (DP) of the electromagnetic laser radiation (20) within the epitaxial semiconductor layer sequence (2) .

12. Semiconductor laser according to any of claims 1 to 10, further comprising a photonic crystal layer (24) enhancing and / or selecting modes of the electromagnetic laser radiation (20) .

13. Semiconductor laser according to the previous claim, wherein- the photonic crystal layer (24) comprises periodically arranged structure elements,- the mode pusher layer (13) comprises a plurality of periodically arranged vias (16) , and- a periodicity of the vias (16) is larger by at least a factor 10 than a periodicity of the structure elements of the photonic crystal layer (24) .

14. Method for manufacturing a semiconductor laser comprising the steps:-providing a substrate (1) ,- epitaxially growing an epitaxial semiconductor layer sequence (2) based on a nitride compound semiconductor material on the growth substrate (1) , the epitaxial semiconductor layer sequence (2) comprising a p-doped region (5) and a n-doped region (6) and an active zone (7) arranged between the p-doped region (5) and the n-doped region (6) , wherein- a mode pusher layer (13) is arranged within the n-doped region (6) or adjacent to the n-doped region (6) ,- the mode pusher layer (13) locates a mode (25) of the electromagnetic laser radiation (20) to overlap with a gain region (8) of the epitaxial semiconductor layer sequence (2) during operation, the gain region (8) being configured for generation of electromagnetic laser radiation (20) during operation,- the mode pusher layer (13) has at least one via (16) .

15. Method according to the previous claim, wherein the at least one via (16) is etched in the mode pusher layer (13) after epitaxial growth of the mode pusher layer (13) .

16. Method according to any of claims 7 or 8, wherein a (Al ) GaN-layer (11) is epitaxially regrown on the mode pusher layer (13) with the at least one via (16) .

17. Method according to the previous claim, wherein the (Al ) GaN-layer (11) is epitaxially regrown by a low temperature process.

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