Semiconductor laser and method for manufacturing a semiconductor laser comprising a feedback element

Description

[0001] The present invention relates to a semiconductor laser according to the preamble of claim 1 and to a method for producing a semiconductor laser according to claim 9.

[0002] In known semiconductor lasers and their manufacturing processes, multilayer structures made of semiconductor materials, insulating materials, and optionally metals are generally formed using appropriate deposition and layer growth processes, and structured using generally known methods such as lithography or etching. All semiconductor lasers have at least one active region in which stimulated emission occurs, enabling the function of a laser.

[0003] There are essentially two differences in the formation of the active region in known semiconductor lasers with regard to the spatial extent of the active region. In semiconductor laser diodes, for example, the active region is generally present over the entire area of ​​the multilayer structure, and localization of the laser radiation is achieved by elements arranged above and / or below the active region, such as waveguides and / or a ridge, which have a corresponding spatial structure. In such semiconductor lasers, it is also known to arrange optical feedback elements above and / or below the active region, which enable mode selection of the laser radiation and thus, in the best case, limit the laser radiation emitted by the semiconductor laser to a single laser mode.

[0004] Apart from such semiconductor lasers, structures are also known in which a spatial limitation of the active region is necessary or at least sensible. This necessity for spatial limitation is generally caused by the problem of current spreading, which refers to the spreading of a pump current within the active region, as a result of which only a spatially less localized and thus inefficient generation of laser radiation can occur. In order to prevent such current spreading within the active region, in such semiconductor lasers, material is usually removed during the structuring of the multilayer structure. This material removal takes place in a material removal direction that is usually perpendicular to a surface of a substrate of the semiconductor laser, and in which at least as much material orso many layers are removed that the active region is also completely removed, at least in part, along the material removal direction and is thus spatially limited in one dimension perpendicular to the layer propagation plane.

[0005] Structuring attempts have already been made for such semiconductor lasers with the aim of arranging an optical feedback element as close as possible to the active region, thus enabling optical feedback and the resulting mode selection of the laser radiation in the active region. For example, the provision of a so-called vertical grating structure is known from US 2006 / 0056472 A1 and the publication "High-power CW performance of 7-stage interband cascade lasers", Canedy CL et al., Proc. of SPIE Vol. 9002, pages 90021C-1 to 90021C-7. However, such structures have proven disadvantageous in several respects. Firstly, their manufacture and the corresponding manufacturing processes are complex. In addition, or precisely for this reason, the percentage yield of lasers that meet the desired specification of spectral single-mode or multi-mode is also very limited.Monomode is very low.

[0006] Furthermore, US 2005 / 0276298 A1 discloses the arrangement of a large number of laser cavities in series for unipolar lasers to achieve mode selection by superimposing the individual spectra. Different arrangements of grating structures can also be used for this purpose.

[0007] US Pat. No. 5,982,804 A also discloses a DFB semiconductor laser having a grating structure formed from a semiconductor material. The upper edge of the semiconductor grating structure can be arranged at the level of the upper edge of the laser's active zone.

[0008] DFB lasers are also known from the documents US 2001 / 0036213 A1 and JP S62-295 480 A, in which a grating structure layer is arranged in the region of the waveguide ridge and the adjacent material removal regions.

[0009] The document US 2012 / 093187 A1 describes a special structure of the waveguide layer for an increased output power of a laser diode, wherein metal gratings laterally to a ridge waveguide define a mode structure of the laser.

[0010] Accordingly, it is an object of the present invention to propose a semiconductor laser with an active region having a layer structure for forming an interband cascade laser and a method for its production, in which or by which an interband cascade laser is provided which does not exhibit current spreading due to a corresponding spatial limitation of the active region and allows effective mode selection of the laser or the laser radiation by means of a corresponding optical feedback element and also realizes the highest possible percentage yield of spectrally monomode lasers.

[0011] This object is achieved by a semiconductor laser according to claim 1 and by a corresponding manufacturing method according to claim 9. Advantageous embodiments of the present invention are the subject of the dependent claims.

[0012] The generic semiconductor laser has a multilayer structure comprising a ridge and, in addition, a material removal region laterally adjacent to the ridge. The multilayer structure is arranged on a substrate, and a layer propagation plane is defined by a surface of the substrate. The ridge comprises at least one active region having a layer structure for forming an interband cascade laser, the at least one active region being spatially delimited by a transition between the ridge and the material removal region in one dimension of the layer propagation plane. According to the generic method, an insulation layer and a grating structure layer arranged thereabove are provided at least in the material removal regions.The semiconductor laser is characterized in that the insulation layer and the grating structure layer are arranged in the material removal areas such that the grating structure layer is located below, but not more than 100 nm below, a lower edge of the active region. The distance should be measured perpendicular to the layer propagation plane or in the growth direction or ablation direction and represent the smallest distance between the lower edge of the active region and the grating structure layer.

[0013] The optical coupling between the grating structure layer and the laser light of the active region is particularly effective because, according to the invention, the grating structure layer comprises metal, in particular chromium. Furthermore, the invention provides that the grating structure layer comprises separate, mutually parallel webs made of metal, in particular chromium, wherein the webs of the grating structure layer are arranged perpendicular to the orientation of the web of the multilayer structure, thus generating optical feedback with the laser radiation in the active region.

[0014] The arrangement of the grating structure layer according to the invention makes it possible for at least an evanescent portion of the wave of the laser radiation, which also extends into the areas outside the active region, to experience optical coupling with the grating structure layer designed as a feedback element, whereby both the requirements for avoiding current spreading due to the spatial limitation of the active region and the requirements for effective mode selection for providing a monomode semiconductor laser are taken into account in a particularly advantageous manner.

[0015] For clarity, the following definition shall be used in this description. With regard to the proposed semiconductor lasers and the described method, the term "bottom" shall refer to a side or a direction that, with respect to the substrate of the semiconductor laser, faces this substrate or points in the direction of the substrate. In other words, this means that the lower edge of the active region is to be understood as the boundary of the active region that faces the substrate. Accordingly, it should also be assumed that the material removal areas are created by material removal that occurs downwards along a direction or along a material removal direction that runs essentially perpendicular to a layer propagation plane formed by a surface of the substrate.The material removal direction therefore runs parallel to the growth direction of the multilayer structure. Accordingly, the term "top" should be understood as a side or direction facing away from the substrate.

[0016] According to an advantageous embodiment, the transitions can be formed just deep enough, or just enough material can be removed in the material removal areas, to remove the active region in its thickness or layer thickness just enough to form the thinnest possible insulation layer, at least in the material removal areas, and a grid structure layer above it. Instead of applying an insulation layer, an insulation layer naturally formed by oxidation beneath the grid structure layer is also suitable for insulation from the grid structure layer. With an ideal etching depth or material removal in the material removal areas, the use of such a natural or self-forming insulation layer can be advantageous.

[0017] It is particularly advantageous for the propagation of the laser light in the active region if the multilayer structure comprises at least one waveguide layer. It can be particularly advantageous if a first and a second waveguide layer are provided, with one waveguide layer being arranged above and one below the active region. If a waveguide layer is arranged above the active region, it is only located in the ridge of the semiconductor laser. This is because the transition between the ridge and the material removal areas to the side of the ridge inevitably limits all layers above the active region spatially in one dimension of the layer propagation plane due to the material removal or the transition. This applies at least to all those layers that were applied above the active region during the manufacturing process before the material removal.

[0018] In other words, this means that a waveguide layer arranged above the active region is spatially confined to the ridge of the semiconductor laser. The same may, but need not, be true for a waveguide layer arranged below the active region, since the transition between the ridge and the material removal areas extends at least far enough to spatially confine the active region. The layers of the multilayer structure arranged below the active region may or may not be affected by such a spatial confinement to the ridge, depending on the amount of material removal.

[0019] In the embodiment already mentioned above, in which the transitions are just deep enough to remove the active region, there is no spatial limitation of a layer or waveguide layer that may be arranged below the active region.

[0020] Furthermore, it is particularly advantageous if the multilayer structure has at least one cladding layer. This cladding layer can also be arranged above or below the active region, in particular above or below a waveguide layer, each facing away from the active region, within the multilayer structure. With regard to the spatial limitation of the cladding layer to the region of the ridge or to the transition and the material removal regions, the relationship stated above for the waveguide layer applies depending on the arrangement of the cladding layer above or below the active region. It can be particularly advantageous for the operation of the semiconductor laser if both a cladding layer is arranged above the active region and a cladding layer is arranged below the active region.

[0021] For both the operation of the semiconductor laser and its manufacture, it has proven particularly desirable if the multilayer structure is constructed mirror-symmetrically with respect to the active region in the layer sequence.

[0022] However, it can also be provided that the multilayer structure has a highly doped upper contact layer or cap layer as the topmost layer, which facilitates electrical contacting of the semiconductor laser. Preferably, the cap layer adjoins a cladding layer perpendicular to the layer propagation plane.

[0023] Furthermore, the semiconductor laser can also be designed such that the transitions have a tail in a section or end section facing the substrate, wherein the tail is designed such that the angle between the transition and the layer propagation plane becomes substantially continuously smaller towards the material removal regions adjacent to the transition.

[0024] It is further advantageous if the extensions are arranged in the lower area of ​​the active region or the lower edge of the active region lies in the area of ​​the extensions of the junctions. In accordance with the generally advantageous arrangement of the lattice structure layer, the insulation layer and the lattice structure layer can also be arranged in the area of ​​the extensions of the junctions. The arrangement of the lattice structure layer and the insulation layer is to be understood as referring to a direction in the layer deposition plane. In other words, it is advantageous if the lattice structure layer is arranged at least in the material removal areas and projects into the transitions, there in particular into the areas of the extensions. Perpendicular to the layer propagation plane, however, the lattice structure layer and the insulation layer can be designed as already described above. The lattice structure layer can therefore be at most 100 nm below the active region ortheir lower edge. In addition, it is particularly desirable if the transitions between the web and the material removal areas are formed at least in sections by a flank each. The flank is created by the material removal. Nevertheless, the flanks should be viewed as a special design of the transition and not assigned to the material removal areas. In other words, the material removal areas should be defined by the fact that they are created by uniform material removal, in the removal direction, in particular perpendicular to the layer propagation plane. Accordingly, the above-mentioned extensions are also to be understood as parts of the transitions or as sections of the flanks, which are also created by material removal, but only border on the material removal areas within the meaning of this description.

[0025] It is particularly advantageous for the manufacture and operation of semiconductor lasers if the flanks are formed as oblique flanks that, at least in sections, enclose an angle of 10° to 90°, in particular 70° to 90°, with the layer propagation plane. The angle of the flank can be selected, in particular, depending on the active region used in order to achieve a particularly good effect or a particularly good coupling of the laser light to the feedback element.

[0026] Furthermore, it is particularly desirable if the insulation layer and / or the grating structure layer are arranged at least partially in the region of the transitions and / or in the region of the flanks and, in particular in the region of the flanks, run essentially parallel to the flanks. If the insulation layer is also arranged in the region of the flanks, this can be achieved, for example, by choosing a method for applying the insulation layer that is non-directional or has no preferred direction during application or deposition. This then creates an insulation layer in the region of the flanks that runs essentially parallel to the flanks. An insulation layer in the region of the flanks serves, for example, to passivate the semiconductor laser in these regions.

[0027] By simultaneously arranging the grid structure layer, at least partially in the region of the flanks and in particular substantially parallel to the flanks, it is particularly advantageous to electrically separate the grid structure layer from the active region by the insulation layer, thereby preventing unwanted current from flowing through the grid structure layer. Furthermore, applying the grid structure layer in the region of the flanks also allows the initial level of the material removal areas on which the insulation layer and the grid structure layer are applied, orthe exact depth of material removal in the material removal direction can be largely neglected and at the same time the condition is met that both along the layer propagation plane and along the material removal direction the grating structure layer can be arranged so close to the active region that an optical feedback between the grating structure layer and the laser radiation in the active region is enabled.

[0028] For an interband cascade laser, the angle between the layer propagation plane and the flank should be as small as possible. Angles of approximately 70° have proven to be practical and reliably producible. However, it is also conceivable and desirable to further reduce this angle. In principle, a reduction of the angle to approximately 10° is both technically feasible and desirable.

[0029] However, if the active region comprises a layer structure used to form a quantum cascade laser, a transition between the ridge and the transitions or flanks that is as right-angled as possible is desirable. In other words, this means that for such an active region, the flank preferably forms an angle of approximately 90° with the layer propagation plane. However, even here, somewhat smaller angles are still more advantageous and significantly easier to manufacture and achieve. Accordingly, angles between 80° and 90° can also be provided for active regions to form a quantum cascade laser.

[0030] The method according to the invention for producing a semiconductor laser comprises the method steps of claim 9, which, however, expressly do not represent the entirety of all method steps.

[0031] Rather, the essential process steps that serve to achieve the effect according to the invention are described or claimed. A multitude of further processing steps, such as those known from manufacturing processes for generic semiconductor lasers and generic grating structure layers, can, purely numerically, represent the majority of the total process steps for manufacturing the semiconductor laser.

[0032] However, it is generally essential that a multilayer structure is first applied to a substrate, wherein the layers of the multilayer structure run parallel to a layer propagation plane defined by a surface of the substrate, and wherein the application of the multilayer structure comprises at least the creation of an active region comprising a layer structure for forming an interband cascade laser.

[0033] In a further generic method step, the removal of material from the multi-layer structure is provided in at least two material removal regions separated from one another, whereby the material removal takes place essentially perpendicular to the layer propagation plane or in the material removal direction and thereby in a region in which no material removal takes place, namely between the material removal regions, a web is formed which is separated from the material removal regions by a transition in each case such that at least the active region is spatially delimited by the transitions in one dimension of the layer propagation plane.

[0034] This is followed, at least indirectly, by the application of an insulation layer to at least the material removal areas and the subsequent application of a grid structure layer at least in the area of ​​the material removal areas.

[0035] The basic idea of ​​the invention is realized in the present method, inter alia, in that the method step of material removal and the method steps of applying the insulation layer and / or the lattice structure layer are coordinated with one another in such a way that the lattice structure layer is arranged below, but not more than 100 nm below, a lower edge of the active region.

[0036] Furthermore, the invention provides that a metal, in particular chromium, is at least deposited and structured to produce the lattice structure layer.

[0037] According to the invention, this is done within the framework of a sub-process which provides for an electron beam lithography process. In this process, a resist which has initially been applied is exposed and developed, then the metal or chromium is deposited, and finally the areas in which the resist was not exposed are lifted off. In this way, separate webs of the feedback element are created in at least the areas of the grating structure layer which contribute to the coupling with the laser light. According to the invention, these webs are arranged perpendicular to the extension of the web of the multilayer structure. Furthermore, according to the invention, the webs have a periodicity in the separate areas, at least in sections. The proposed method for manufacturing a semiconductor laser ensures that, on the one hand, current spreading is prevented in the active region, which is achieved by material removal which also encompasses or covers at least the full height of the active region.The active region is limited to the ridge. Furthermore, the method according to the invention achieves mode selection of the laser radiation using a grating structure layer, for example, designed as a DFB structure, in such a way that a higher process tolerance regarding the arrangement of the grating structure layer is enabled during the process. This, in turn, leads to a higher percentage yield of single-mode semiconductor lasers and consequently to lower manufacturing costs.

[0038] In other words, this means that the three process steps of material removal, application of the insulation layer, and application of the grid structure layer can be coordinated with each other with regard to the removal depth and the layer thicknesses of the applied insulation layer and grid structure layer, so that the grid structure layer is ultimately located no more than 100 nm below the lower edge of the active region. Overall, the accuracy or uncertainty in one of the aforementioned process steps can be compensated for by the other two process steps, so that the relative arrangement of the grid structure layer with respect to the lower edge of the active region can ultimately be achieved.

[0039] It is particularly advantageous for the semiconductor laser to be manufactured if it has at least one waveguide layer and / or a cladding layer above or below the active region. Accordingly, an advantageous embodiment of the proposed method provides that the production of the multilayer structure or the application of the multilayer structure comprises the application of at least one waveguide layer and / or the application of at least one cladding layer.

[0040] For example, it can be provided that a waveguide layer is arranged directly above and below the active region, and that a cladding layer is arranged above the upper waveguide layer and below the lower waveguide layer. In a preferred embodiment of the method, the material removal forms extensions in a section or end section of the transitions facing the substrate, wherein the extensions are configured such that the angle between the transition and the layer propagation plane becomes substantially continuously smaller toward the material removal regions adjacent to the transition.

[0041] In addition, the proposed method can be designed such that the transitions between the ridge and the material removal regions are formed, at least in sections, in the form of a flank each as a result of the material removal, and that the material removal takes place, in particular, such that the flanks are formed, at least in sections, as oblique flanks and enclose an angle of 10° to 90°, in particular between 70° and 90°, with the layer propagation plane of the substrate. As already explained with reference to the disclosed device or the disclosed semiconductor laser, the choice of the angle between a flank for forming a transition between the ridge and a material removal region can depend on the shape or mode of operation of the active region, wherein, in particular in the case of an active region for forming an interband cascade laser, the smallest possible angles, in particular angles between 10° and 70°, are provided orare desirable and in an active region having such a layer system that enables the formation of a quantum cascade laser, flanks are produced at a right angle to the layer propagation plane, namely flanks with an angle between approximately 80° and 90° with respect to the layer propagation plane of the substrate.

[0042] In a further particularly advantageous embodiment of the proposed method, the insulation layer and / or the grid structure layer are arranged during application or the application of the layers is controlled such that the insulation layer and / or the grid structure layer are arranged at least partially in the region of the transitions and / or in the region of the flanks and run essentially parallel to the flanks in the region of the flanks.

[0043] This achieves passivation by means of the insulation layer and electrical insulation of the transitions or flanks.

[0044] In addition, a particularly good and effective coupling between the laser radiation in the active region and the grating structure layer can be achieved.

[0045] In the following, individual advantageous embodiments of the semiconductor laser according to the invention and of the method according to the invention are explained by way of example with reference to the merely schematic drawings.

[0046] They show: Fig. 1A to 1C show exemplary stations of the manufacturing method of a semiconductor laser according to the invention, as well as a substantially completed semiconductor laser according to the invention; Fig. 2 shows a section through a semiconductor laser according to the invention in a first alternative embodiment; Fig. 3 shows a section through a semiconductor laser according to the invention in a second alternative embodiment; Fig. 4 shows a section through a semiconductor laser according to the invention in a third alternative embodiment; Fig. 5 shows a section detail through a semiconductor laser according to the invention in a fourth alternative embodiment; Fig. 6 shows a section through a semiconductor laser according to the invention in a fifth alternative embodiment; Fig. 7 shows a section through an example of a semiconductor laser for a better understanding of the invention.

[0047] Fig. 1A shows a process or method stage during the method according to the invention for producing a semiconductor laser 01 according to the invention. In Fig. 1A A multilayer structure 04 has already been applied to a substrate 02 by generally known process steps or epitaxial steps. The multilayer structure 04 comprises, in the order of the applied layers or from bottom to top, a first cladding layer 06 or a lower cladding layer 06, a first or lower waveguide layer 08, an active region 10 and a second or upper waveguide layer 12, and finally a second or upper cladding layer 14. The active region 10 can itself consist of a plurality of individual layers, which can include, for example, injector layers.

[0048] Fig. 1B shows a process or method stage which represents an intermediate product for the production of the semiconductor according to the invention after the material removal. As in Fig. 1B can be seen, compared to the Fig. 1A In the material removal areas 16, 18, the previously applied layers are completely removed except for the lower cladding layer 06, and the lower cladding layer 06 is also partially removed. As a result, the web 20 is formed between the material removal areas 16 and 18, which is separated from the material removal areas by the transitions 22 and 24 such that the active region 10 is spatially limited in a spatial direction of the layer propagation plane 26, thereby overcoming the current spreading within the active region 10.

[0049] In the Fig. 1B The present invention is described below in such a way that, during the material removal, not all layers of the multi-layer structure are completely removed, but rather the bottommost layer or layer bordering the substrate is partially retained. This is done, however, only for illustrative purposes. To implement the invention, however, it can equally be provided that all layers of the multi-layer structure are completely removed by the material removal and thus, after the material removal, the substrate or a substrate surface is or is exposed in the material removal areas 16 and 18. On the other hand, it can also be provided that the material removal only takes place until at least the active region 10 is spatially delimited and a layer or layers arranged below the active region remains or remain unaffected by the material removal or is or are only partially removed.Likewise, all figures show a symmetrical structure of the multilayer structure 04 with respect to the active region 10 in terms of the layer sequence. This is an advantageous embodiment, although other, deviating layer sequences can also be advantageously provided.

[0050] The Fig. 1C shows a schematic perspective view of a semiconductor laser 01 after completion of the method according to the invention. Compared to the process or process state of the Fig. 1B are in the Fig. 1C At least in the material removal areas 16 and 18, an insulation layer 28 and a grid structure layer 30 have been applied or produced. As can be seen from the Fig. 1C As can be seen, the upper edge of the grating structure layer 30 is essentially at the same height as the lower edge of the active region 10. This enables a particularly effective optical coupling between the laser radiation in the active region 10 and the grating structure layer 30, which accordingly leads to a very precise mode selection of the semiconductor laser 01.

[0051] However, as will be seen from the further description, especially regarding the Fig. 2 and the Fig. 6 This arrangement of the lattice structure layer 30 with respect to the active region 10 of the Fig. 1C not the only possible or sensible configuration. In general, the lattice structure layer can be arranged such that its position relative to the active region perpendicular to the layer propagation plane either allows an overlap of the lattice structure layer 30 and the active region 10, or the lattice structure layer 30 is arranged at least no more than 100 nm below the active region 10 or its lower edge.

[0052] As from Fig. 1C As is easily apparent, the corresponding arrangement of the lattice structure layer with respect to the active region can be achieved or adjusted in a relatively simple manner, since this can be adjusted through the successive process steps of material removal, the application of the insulation layer 28, and the subsequent application of the lattice structure layer 30. In other words, this means that the layer thickness of the insulation layer 28 or the lattice structure layer 30 can be adjusted depending on how much material was removed by the material removal, and thus the corresponding or claimed arrangement of the lattice structure layer can be easily achieved, at least at the level of the lower edge of the active region 10. Instead of an additionally applied insulation layer 28, the insulation layer can also be produced by oxidation of the surfaces exposed by the material removal.Rather, "generated" means that the insulating layer 28 forms itself or naturally upon exposure to oxygen. Fig. 2 shows a section through a semiconductor laser according to the invention. In addition to the material removal areas 16 and 18 and the web 20, the Fig. 2 a transition 22 or 24 between the web and the respective material removal areas 16 and 18, wherein the transition 22 and 24 is formed by the flanks 32 and 34, wherein the flanks 32, 34 each enclose an angle of approximately 80° with the layer spreading plane 26, as in Fig. 2 indicated by the sketch of the angle α.

[0053] As from Fig. 2 It can also be seen that in the embodiment of the semiconductor laser 01 shown there, the insulation layer 28 and the structural layer 30 are not exclusively arranged in the region of the material removal regions 16 and 18, but also in the region of the transitions 22 and 24, whereby, however, in the region of the transitions 22 and 24, the grating structure layer 30 still runs essentially parallel to the layer propagation plane 26. Also in Fig. 2 The advantageous embodiment is shown, according to which the grating structure layer 30 or its upper edge does not end flush with the lower edge of the active region 10, but also extends or is arranged above the lower edge of the active region. As a result, the coupling between the laser radiation of the active region 10 and the grating structure layer 30 can be increased compared to the illustration of the Fig. 1C be further improved.

[0054] Fig. 3 shows a modification of the semiconductor laser 01 compared to the Fig. 2 , which arises because the insulation layer 28 is arranged not only in the area of ​​the material removal areas 16 and 18, but also in the entire area of ​​the transitions 22 and 24 and in the area of ​​the web 20. In this case, it can be provided that the method for producing the semiconductor laser 01, before applying the insulation layer 28, first provides a method step by means of which a further removal of a naturally forming or naturally formed passivation layer or oxide layer takes place on the entire exposed surface after the material removal and then the insulation layer 28 is applied over all areas. As in the Fig. 3 As shown, the lattice structure layer 30 is also provided or arranged in the entire area of ​​the transitions 22 and 24 and also substantially parallel to the flanks 32 and 34. Even if the lattice structure layer is thereby separated from the active region 10 by the insulation layer 28, the Fig. 3 However, the illustrated embodiment of the semiconductor laser 01 means that the grating structure layer 30, which lies with its lower edge 31 below the lower edge of the active region 10, extends in the direction of the material removal direction over the full height of the active region and thus a particularly effective optical coupling between the laser radiation in the active region 10 and the grating structure layer can be achieved.

[0055] From the presentation of the Fig. 3 Another significant advantage of the present embodiment becomes clear. By arranging the lattice structure layer in the region of the flanks 32, 34, the relative arrangement according to the invention between the lattice structure layer 30 and the active region 10 is automatically achieved starting at a certain material removal depth.In other words, this means that even with a correspondingly greater material removal in the material removal regions 16 and 18 and correspondingly deeper material removal regions 16, 18, the desired arrangement of the lattice structure layer 30 with respect to the active region 10 is inevitably achieved by the arrangement of the insulation layer and the lattice structure layer in the region of the flanks 32, 34, since the parts of the lattice structure layer 30 in the region of the flanks 32, 34 always achieve the arrangement of the lattice structure layer 30 of no more than 100 nm below the active region, optionally at the level of the lower edge of the active region 10 or above, as soon as the depth of the material removal plus the thickness of the insulation layer 28 amounts to at least 100 nm below the lower edge of the active region.However, this means that when the grating structure layer 30 is arranged in the region of the transitions 22, 24 or flanks 32, 34, the removal depth of the material removal regions can be neglected, which enables a significantly simplified production of the semiconductor lasers.

[0056] The Fig. 4 shows a modification compared to the Fig. 3 , in which the application of the insulation layer 28 and the grid structure layer 30 in the area of ​​the upper cladding layer 14 or across the width of the web 20 was removed again. This removal can be carried out in order to create a Fig. 4 to expose the highly doped upper contact layer or cap layer (not shown).

[0057] Fig. 5 shows a section of a semiconductor laser 01 according to the invention. The transition 22 is designed as a flank 32 in the upper section. In the section of the transition 22 facing the substrate 02, this has a tail 23. As indicated by the angles α 1 and α 2, the angle between the transition and the layer spreading plane 26 becomes continuously smaller laterally towards the material removal region 16 adjacent to the transition. However, "continuous" is not to be understood in the strictly mathematical sense. In other words, the tail 23 is designed such that the transition transitions into the material removal region 16 via a rounded region. The material removal in the Fig. 5 just deep enough so that the material removal area 16 is located minimally below the lower edge of the active region. The insulation layer 28 is correspondingly formed such that the lower edge 31 of the lattice structure layer and the lower edge of the active region 10 are at the same level, as indicated by the horizontal dotted line 25.

[0058] In Fig. 5 It can be seen that the insulation layer 28 and the lattice structure layer 30 are arranged in the material removal region 16, in the region of the extension 23 of the transition 22 and in the region of the flank 32 of the transition 22.

[0059] The Fig. 6 shows a modification of the Fig. 5 . Also in the Fig. 6 the transition 22 is formed by a flank 32 in the upper region of the transition 22 and by a tail 23 in a section of the transition 22 facing the substrate 02. In contrast to the Fig. 5 is, however, in the Fig. 6 More material has been removed in the material removal region 16. The grating structure layer 30 is applied to the insulation layer 28. However, the insulation layer 28 is only thick enough to position the grating structure layer 30 below the lower edge of the active region 10. The distance between the lower edge of the active region 10 and the grating structure layer 30 perpendicular to the layer propagation plane 26 is indicated by the distance d. For coupling between the laser radiation in the active region 10 and the grating structure layer 30, it is necessary that the distance d is not greater than 100 nm.

[0060] In Fig. 7 An example is further shown for a better understanding of the invention, in which, in comparison to the Fig. 6 a smaller or less deep material removal has occurred in the material removal area 16. Accordingly, the insulation layer 28 and the lattice structure layer 30 are arranged higher perpendicular to the layer propagation plane 26 than in Fig. 6 As indicated by the dotted horizontal lines in Fig. 7 As indicated, there is an overlap 35 between the lower edge of the active region 10 and the grating structure layer 30. In other words, this means that the grating structure layer is arranged at the level of the lower edge of the active region 10 and above in the area of ​​the extension 23. This arrangement also allows for effective coupling of the laser light in the active region 10 to the grating structure layer 30, resulting in effective mode selection.

Claims

1. A semiconductor laser (01) having a multilayer structure (04) comprising a ridge (20) and two material removal areas (16, 18) adjacent to the ridge (20) on either side, the multilayer structure (04) being arranged on a substrate (02) and a layer expansion plane (26) being defined by a surface of the substrate (02), the ridge (20) having at least one active region (10) and at least the active region (10) being spatially limited by passages (22, 24) between the ridge (20) and the material removal areas (16, 18) in one dimension of the layer expansion plane (26), the active region (10) having a layer structure for forming an interband cascade laser, wherein, at least in the material removal areas (16, 18), an insulation layer (28) and a superimposed grating structure layer (30) are provided, the insulation layer (28) and the grating structure layer (30) being arranged in the material removal areas (16, 18) in such a manner that the grating structure layer (30) is arranged below, but not more than 100 nm below, a bottom edge of the active region (10), the grating structure layer (30) comprising a metal and being formed by grating webs that are periodic at least in sections, the grating structure layer (30) having separate parallel webs made of the metal, said grating webs of the grating structure layer (30) being arranged perpendicularly to the orientation of the ridge (20) of the multilayer structure (04) so that an optical feedback with a laser radiation in the active region (10) is produced.

2. The semiconductor laser (01) according to claim 1, characterized in that the multilayer structure (04) has at least one waveguide layer (08, 12).

3. The semiconductor laser (01) according to any one of claims 1 or 2, characterized in that the multilayer structure (04) has at least one cladding layer (06, 14).

4. The semiconductor laser (01) according to claim 3, characterized in that perpendicularly to the layer expansion plane (26), a highly doped upper contact layer is adjacent to a cladding layer (14).

5. The semiconductor laser (01) according to any one of claims 1 to 4, characterized in that the passages (22, 24) each have an extension (23) in a section that faces the substrate (02), the angle between the passage (22) and the layer expansion plane (26) becoming continuously smaller toward the material removal area (16) adjacent to the passage (22) by way of the extension (23).

6. The semiconductor laser (01) according to any one of claims 1 to 5, characterized in that at least in sections, the passages (22, 24) between the ridge (20) and the material removal areas (16, 18) are each formed by a flank (32, 34).

7. The semiconductor laser (01) according to claim 6, characterized in that at least in sections, the flanks (32, 34) are formed by an inclined flank and form an angle of 10° - 90°, in particular of 70° - 90°, with the layer expansion plane (26).

8. The semiconductor laser (01) according to any one of claims 1 to 7, characterized in that the insulation layer (28) and / or the grating structure layer (30) are arranged at least in part in the area of the passages (22, 24) and / or in the area of the flanks (32, 34).

9. A method for producing a semiconductor laser (01) comprising the method steps of: - applying a multilayer structure (04) onto a substrate (02), the layers of the multilayer structure (04) running parallel to a layer expansion plane (26) defined by a surface of the substrate (02) and the application of the multilayer structure (04) comprising at least the production of an active region (10) having a layer structure for forming an interband cascade laser; - removing material of the multilayer structure (04) in two separate material removal areas (16, 18), the material being removed substantially perpendicularly to the layer expansion plane (26) and a ridge (20) thus being formed that is separated from the material removal areas (16, 18) by passages (22, 24) in such a manner that at least the active region (10) is spatially limited by the passages (22, 24) in one dimension of the layer expansion plane (26); - producing an insulation layer (28) at least on the material removal areas (16, 18); - applying a grating structure layer (30) at least in the area of the material removal areas (16, 18), the removal of material and the application of the insulation layer (28) and / or of the grating structure layer (30) being coordinated in such a manner that the grating structure layer (30) is arranged below, but not more than 100 nm below, a bottom edge of the active region (10), wherein a metal is at least deposited and structured so as to produce the grating structure layer, such that, at least in the areas of the grating structure layer (30) that aid coupling with the laser light, separate grating webs made of metal are formed, said grating webs being arranged perpendicularly to the expansion of the ridge (20) of the multilayer structure (04) and, at least in sections, exhibiting periodicity in separate areas.

10. The method according to claim 9, characterized in that the application of the multilayer structure (04) comprises the application of at least one waveguide layer (08, 12) and / or the application of at least one cladding layer (06, 14).

11. The method according to any one of claims 9 or 10, characterized in that by removing the material, an extension is formed in a section of the passages (22, 24) that faces the substrate, the extension being formed in such a manner that the angle between the passage (22) and the layer expansion plane (26) becomes continuously smaller toward the material removal area (16) adjacent to the passage.

12. The method according to any one of claims 9 to 11, characterized in that by removing the material, the passages (22, 24) between the ridge (20) and the material removal areas (16, 18) are each formed, at least in sections, in the shape of a flank (32, 34) and, in particular, that the material is removed in such a manner that the flanks (32, 34) are formed, at least in sections, as inclined flanks and form an angle of 10° - 90°, in particular of 70° - 90°, with the layer expansion plane (26) of the substrate (02).

13. The method according to any one of claims 9 to 12, characterized in that the insulation layer (28) and / or the grating structure layer (30) are arranged at least in part in the area of the passages (22,24) and / or in the area of the flanks (32, 34).