Patent Publication Number: US-2018048114-A1

Title: Edge-emitting semiconductor laser and method for the production thereof

Description:
TECHNICAL FIELD 
     This disclosure relates to an edge-emitting semiconductor laser and a method of producing an edge-emitting semiconductor laser. 
     BACKGROUND 
     It is known that the mirror facets in edge-emitting semiconductor lasers are exposed to high electrical, optical and thermal stresses. Absorption losses at the mirror facets may lead to heating of the mirror facets and ultimately to their thermal destruction. 
     It could therefore be helpful to provide an edge-emitting semiconductor laser, the mirror facets of which are less susceptible to thermal destruction. 
     SUMMARY 
     We provide an edge-emitting semiconductor laser including a semiconductor structure having a substrate and a layer sequence arranged over an upper side of the substrate and having layers lying above one another along a growth direction, wherein a lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer and an upper cladding layer follow one another in the layer sequence, the semiconductor structure is laterally bounded by a first facet and a second facet, the semiconductor structure has a central section and a first edge section adjacent to the first facet, the layer sequence is offset relative to the central section in the growth direction in the first edge section such that, in the first edge section, one of the cladding layers or one of the waveguide layers is arranged in the growth direction at a height of the active layer in the central section, the layer sequence includes an epitaxially grown additional layer arranged between the upper side of the substrate and the lower cladding layer at least in the first edge section, the additional layer is not arranged between the upper side of the substrate and the lower cladding layer in the central section, and the additional layer is electrically insulating or has doping with the opposite sign to the lower cladding layer. 
     We also provide a method of producing an edge-emitting semiconductor laser including providing a substrate having an upper side; arranging an additional layer on the upper side of the substrate by epitaxial growth; removing a part of the additional layer in a central section to form, on an upper side of the substrate, a surface having a different height in the central section than in a first edge section; depositing a layer sequence over the surface, wherein deposition of the layer sequence includes deposition of a lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer and an upper cladding layer, the additional layer is electrically insulating or has doping with the opposite sign to the lower cladding layer, a height difference of the surface between the central section and the first edge section is dimensioned such that, in the first edge section, one of the cladding layers or one of the waveguide layers is arranged at the height of the active layer in the central section; and fracturing the substrate and the layer sequence such that a first facet, to which the first edge section is adjacent, is formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic sectional side view of a semiconductor structure of an edge-emitting semiconductor laser according to a first example. 
         FIG. 2  shows a schematic sectional side view of a semiconductor structure of an edge-emitting semiconductor laser according to a second example. 
         FIG. 3  shows a schematic sectional side view of a semiconductor structure of an edge-emitting semiconductor laser according to a third example. 
         FIG. 4  shows a schematic sectional side view of a semiconductor structure of an edge-emitting semiconductor laser according to a fourth example. 
         FIG. 5  shows a schematic sectional side view of a semiconductor structure of an edge-emitting semiconductor laser according to a fifth example. 
         FIG. 6  shows a schematic sectional side view of a semiconductor structure of an edge-emitting semiconductor laser according to a sixth example. 
         FIG. 7  shows a schematic sectional side view of a semiconductor structure of an edge-emitting semiconductor laser according to a seventh example. 
         FIG. 8  shows a schematic sectional side view of a semiconductor structure of an edge-emitting semiconductor laser according to an eighth example. 
     
    
    
     LIST OF REFERENCES 
     
         
         
           
               10  edge-emitting semiconductor laser 
               11  edge-emitting semiconductor laser 
               12  edge-emitting semiconductor laser 
               13  edge-emitting semiconductor laser 
               14  edge-emitting semiconductor laser 
               15  edge-emitting semiconductor laser 
               16  edge-emitting semiconductor laser 
               17  edge-emitting semiconductor laser 
               20  semiconductor structure 
               100  substrate 
               101  upper side 
               110  upper metallization 
               120  step 
               200  layer sequence 
               201  growth direction 
               210  lower cladding layer 
               220  lower waveguide layer 
               230  active layer 
               240  upper waveguide layer 
               250  upper cladding layer 
               260  additional layer 
               270  step 
               280  ramp 
               300  central section 
               400  first facet 
               410  first edge section 
               420  first transition section 
               430  first offset 
               440  width 
               500  second facet 
               510  second edge section 
               520  second transition section 
               530  second offset 
           
         
       
    
     DETAILED DESCRIPTION 
     Our edge-emitting semiconductor laser comprises a semiconductor structure having a layer sequence that has layers lying above one another along a growth direction. The semiconductor structure is laterally bounded by a first facet and a second facet. The semiconductor structure has a central section and a first edge section adjacent to the first facet. The layer sequence is offset relative to the central section in the growth direction in the first edge section. 
     Because the layer sequence of the semiconductor structure of this edge-emitting semiconductor laser is offset relative to the central section in the first edge section, light excited in the semiconductor structure is guided in different layers of the layer sequence in the first edge section than in the central section. These other layers have a higher band gap so that absorption of light in the first edge section is impeded or entirely prevented. The first facet and the first edge section adjacent to the first facet, therefore, form a nonabsorbing mirror. This nonabsorbing mirror has only low mirror losses so that only minor heating of the first facet and the first edge section adjacent to the first facet occurs during operation of the edge-emitting semiconductor laser. In this edge-emitting semiconductor laser, there is therefore only a reduced risk of temperature-dependent ageing effects and thermal destruction. 
     A lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer and an upper cladding layer follow one another in the layer sequence. In this case, in the first edge section, one of the cladding layers or one of the waveguide layers is arranged in the growth direction at the height of the active layer in the central section. The effect advantageously achieved by this is that light guided in the waveguide layers in the central section of the semiconductor structure is guided at least partially in one of the cladding layers in the first edge section so that the first facet and the first edge section, adjacent to the first facet, of the semiconductor structure form a nonabsorbing mirror. 
     The semiconductor structure may have a second edge section adjacent to the second facet. In this case, the layer sequence is offset relative to the central section in the growth direction in the second edge section. Advantageously, the second facet and the second edge section adjacent to the second facet of the semiconductor structure then also form a nonabsorbing mirror. This also reduces the risk of thermal destruction in the edge-emitting semiconductor laser in the region of the second facet. 
     The offset of the layer sequence in the second edge section may correspond to the offset of the layer sequence in the first edge section. In this way, the semiconductor structure of the edge-emitting semiconductor laser has a symmetrical configuration that can advantageously be produced particularly simply and economically. 
     The layer sequence lies higher in the growth direction in the first edge section than in the central section. The effect achieved in this way is that in the first edge section, a layer which, in the central section, is arranged below the active layer is adjacent to the active layer in the central section. 
     The semiconductor structure comprises a substrate. The layer sequence is arranged over an upper side of the substrate. The layer sequence comprises an additional layer arranged between the upper side of the substrate and the lower cladding layer at least in sections. This additional layer has a different height in the growth direction in the central section than in the first edge section. The height variation of the additional layer advantageously continues in the rest of the layer sequence arranged over the additional layer so that there is an offset between the first edge section and the central section in the layer sequence. 
     The additional layer is electrically insulating or has doping with the opposite sign to the lower cladding layer. The additional layer is not arranged between the upper side of the substrate and the lower cladding layer in the central section. The insulating additional layer may be configured as an undoped epitaxial layer, as a CVD diamond layer or as a dielectric layer, for example. Advantageously, this additional layer blocks a current path through the layer sequence in the first edge section of the semiconductor structure. No laser light is therefore excited in the first edge section of the semiconductor structure. In this way, possible absorption losses at the first facet and in the first edge section, adjacent to the first facet, of the semiconductor structure are advantageously reduced further. 
     The semiconductor structure may have a first transition section between the central section and the first edge section. In this case, the layer sequence continues continuously between the central section, the first transition section and the first edge section. Advantageously, the semiconductor structure can therefore be produced particularly simply. 
     The central section may lie at a distance of 0.1 μm to 100 μm from the first facet, preferably at a distance of 1 μm to 20 μm. Advantageously, we found such a distance to be particularly effective for the formation of a nonabsorbing mirror in the region of the first facet and the first edge section adjacent to the first facet. 
     A contact layer and an upper metallization may be arranged over the layer sequence. In this case, the upper metallization is arranged only over the central section and not over the first edge section. The effect advantageously achieved by this is that the semiconductor structure of the edge-emitting semiconductor laser is supplied with current during operation of the edge-emitting semiconductor laser only in the central section, but not in the first edge section. No laser light is therefore excited in the first edge section of the semiconductor structure so that possible absorption losses at the first facet and in the first edge section adjacent to the first facet are reduced further. 
     A method of producing an edge-emitting semiconductor laser comprises steps of providing a substrate having an upper side, applying, on the upper side of the substrate, a surface having a different height in a central section than in a first edge section, depositing a layer sequence over the surface, and fracturing the substrate and the layer sequence such that a first facet to which the first edge section is adjacent is formed. 
     The edge-emitting semiconductor laser that may be obtained by this method has a semiconductor structure, the layer sequence of which is offset in the growth direction in a first edge section, which is adjacent to the first facet, relative to the central section. In this way, the first facet, and the first edge section, adjacent to the first facet, of the semiconductor structure of this edge-emitting semiconductor laser act as a nonabsorbing mirror. This nonabsorbing mirror offers the advantages that no absorption losses, or only minor absorption losses, occur in the region of the nonabsorbing mirror so that no heating, or only minor heating, of the first facet and the first edge section adjacent to the first facet occur. In this way, furthermore, only minor ageing effects occur in the region of the first facet so that the risk of thermal destruction of the first facet of the semiconductor structure of the edge-emitting semiconductor laser which can be obtained by the method is reduced. 
     The method of producing the edge-emitting semiconductor laser advantageously makes do without diffusion processes or implantation processes so that it can be carried out simply and in a controlled way. This leads to good reproducibility, which can make a high yield possible during production. The method furthermore advantageously requires no processing operations at high temperature so that damage associated with high-temperature processes to an active layer of the semiconductor structure of the edge-emitting semiconductor laser which can be obtained by the method is avoided. Damage associated with high-temperature processes to electrical contacts of the edge-emitting semiconductor laser is also avoided so that an undesired increase in the operating voltage of the edge-emitting semiconductor laser which can be obtained by the method is also avoided. Other reductions caused by high-temperature processes and/or implantation processes or diffusion processes of the lifetime to be expected for the edge-emitting semiconductor laser are also advantageously avoided. 
     Application of the surface comprises steps of arranging an additional layer on the upper side of the substrate and of removing a part of the additional layer. In this method, a height, varying over the upper side of the substrate, of the additional layer is carried over into the layer sequence deposited over the additional layer so that there is an offset in the growth direction between the first edge section and the central section in the semiconductor structure of the edge-emitting semiconductor laser which can be obtained by the method. 
     Removal of the additional layer may be carried out by an etching method. The etching method may, for example, be a dry etching method. Since removal of the substrate or the additional layer is carried out before the growth of the layer sequence, such an etching method advantageously leads to no damage, or only minor damage, of an active layer of the layer sequence of the semiconductor laser which can be obtained by the method. 
     Deposition of the layer sequence comprises deposition of a lower cladding layer, a lower waveguide layer, an active layer, an upper waveguide layer and an upper cladding layer. In this case, the height difference of the surface between the central section and the first edge section is dimensioned such that, in the first edge section, one of the cladding layers or one of the waveguide layers is arranged at the height of the active layer in the central section. The effect advantageously achieved by this is that light guided in the waveguide layers in the central section of the semiconductor structure is guided at least partially in one of the cladding layers in the first edge section so that the first facet and the first edge section act as a nonabsorbing mirror. 
     The above-described properties, features and advantages, as well as the way in which they are achieved, will become more clearly and readily comprehensible in conjunction with the following description of the examples, which will be explained in more detail in connection with the drawings. 
       FIG. 1  shows a schematic sectional side view of a semiconductor structure  20  of an edge-emitting semiconductor laser  10 . The edge-emitting semiconductor laser  10  may also be referred to as a diode laser. The edge-emitting semiconductor laser  10  may, for example, be provided for emission of light in a wavelength in the UV spectral range, in the visible spectral range or in the infrared spectral range. The semiconductor structure  20  of the edge-emitting semiconductor laser  10  may, for example, be based on an AlInGaN, an AlGaAs or an InGaAlP material system. 
     The semiconductor structure  20  of the edge-emitting semiconductor laser  10  has a substrate  100  and a layer sequence  200  grown epitaxially over an upper side  101  of the substrate  100 . The layer sequence comprises a multiplicity of layers, which lie above one another along a growth direction  201 . The growth direction  201  is oriented perpendicularly to the upper side  101  of the substrate  100 . 
     The semiconductor structure  20  is laterally bounded by a first facet  400  and by a second facet  500 , lying opposite the first facet  400 . The first facet  400  and the second facet  500  are oriented substantially parallel to the growth direction  201 . The first facet  400  and the second facet  500  have been formed after epitaxial growth of the layer sequence  200  by fracturing the semiconductor structure  20 . 
     A resonator of the edge-emitting semiconductor laser  10  extends between the first facet  400  and the second facet  500 . The first facet  400  forms a light-emitting laser facet of the edge-emitting semiconductor laser  10 . During operation of the edge-emitting semiconductor laser  10 , laser light is emitted at the first facet  400  in a direction perpendicular to the first facet  400 . 
     The semiconductor structure  20  of the edge-emitting semiconductor laser  10  has a central section  300  and a first edge section  410  adjacent to the first facet  400 . The central section  300  and the first edge section  410  are arranged next to one another in a direction parallel to the upper side  101  of the substrate  100 , and are directly adjacent to one another in the semiconductor structure  20  of the edge-emitting semiconductor laser  10 . 
     The first edge section  410  has a width of  440 , measured from the first facet  400  and in a direction perpendicular to the first facet  400 . The width  440  may, for example, be 0.1 μm to 100 μm, in particular, for example, 1 μm to 20 μm. This means that, in the semiconductor structure  20  of the edge-emitting semiconductor laser  10 , the central section  300  lies at a distance from the first facet  400  which corresponds to the width  440  of the first edge section  410 . 
     In the first edge section  410 , the layer sequence  200  of the semiconductor structure  20  of the edge-emitting semiconductor laser  10  is offset in the growth direction  201  relative to the central section  300 . In this case, the layers of the layer sequence  200  lie higher in the growth direction  201  in the central section  300  of the semiconductor structure  20  than in the first edge section  410 . An essentially step-like first offset  430  in the layer sequence  200  is therefore formed between the central section  300  and the first edge section  410 . 
     A step  120  is configured on the upper side  101  of the substrate  100  of the semiconductor structure  20 . In this case, the upper side  101  of the substrate  100  lies lower in the growth direction  201  in the first edge section  410  than in the central section  300  so that the step  120  is formed at the boundary between the edge section  410  and the central section  300 . The different height in the growth direction  201  of the upper side  101  of the substrate  100  in the central section  300  and in the first edge section  410  has been carried over during epitaxial growth of the layer sequence  200  onto the upper side  101  of the substrate  100  into the layer sequence  200  so that the first offset  430  has been formed. 
     The step  120  on the upper side  101  of the substrate  100  may, for example, have been formed by a part of the substrate  100  having been removed in the first edge section  410  before the epitaxial growth of the layer sequence  200 . The removal of the part of the substrate  100  may, for example, have been carried out by etching, in particular, for example, by a dry etching method. 
     In the example of the semiconductor structure  20  of the edge-emitting semiconductor laser  10  as shown in  FIG. 1 , the layer sequence  200  comprises a lower cladding layer  210 , a lower waveguide layer  220 , an active layer  230 , an upper waveguide layer  240  and an upper cladding layer  250 , which follow one another in the growth direction  201  in the order stated. The lower cladding layer  210  lies closest to the substrate  100 , and may in particular be arranged directly on the upper side  101  of the substrate  100 . The layer sequence  200  could, however, also comprise even further layers. In particular, further layers could be arranged between the substrate  100  and the lower cladding layer  210  and above the upper cladding layer  250 . 
     The lower cladding layer  210  and the lower waveguide layer  220  of the layer sequence  200  have doping with a first sign, for example, n-doping. The upper waveguide layer  240  and the upper cladding layer  250  of the layer sequence  200  have doping with an opposite sign compared to the doping of the lower cladding layer  210  and the lower waveguide layer  220 , for example, p-doping. 
     The lower cladding layer  210  and the upper cladding layer  250  of the layer sequence  200  comprise a first material. The lower waveguide layer  220  and the upper waveguide layer  240  comprise a second material. The material of the lower cladding layer  210  and the upper cladding layer  250  has a lower refractive index than the material of the lower waveguide layer  220  and the upper waveguide layer  240 . The lower cladding layer  210  and the upper cladding layer  250  have an increased band gap compared to the waveguide layers  220 ,  240 . 
     The active layer  230  of the layer sequence  200  may, for example, be configured as a quantum well or quantum film, or as a two-dimensional arrangement of quantum dots. 
     The first offset  430  in the layer sequence  200 , between the first edge section  410  and the central section  300 , is dimensioned such that, in the first edge section  410 , the upper cladding layer  250  is arranged in the growth direction  201  at the height of the active layer  230  in the central section  300 . As an alternative, it is possible to configure the first offset  430  such that, in the first edge section  410  the upper waveguide layer  240  is arranged in the growth direction  201  at the height of the active layer  230  in the central section  300 . 
     Light generated in the active layer  230  in the central section  300  of the semiconductor structure  20  of the edge-emitting semiconductor laser  10  is guided in the central section  300  in the waveguide layers  220 ,  240  between the cladding layers  210 ,  250 . In the first edge section  410 , however, the light is guided at least partially in the upper cladding layer  250 . The latter has an increased band gap compared to the waveguide layers  220 ,  240  so that the light guided in the first edge section  410  in the upper cladding layer  250  cannot be absorbed, or can be absorbed only to a small extent, in the first edge section  410 . The first facet  400  and the first edge section  410 , adjacent to the first facet  400 , of the semiconductor structure  20  of the edge-emitting semiconductor laser  10  therefore form a nonabsorbing mirror. 
     The first facet  400  and/or the second facet  500  of the semiconductor structure  20  of the edge-emitting semiconductor laser  10  may have coatings (not represented in  FIG. 1 ), which may be used for passivation and/or antireflection or to increase reflectivity. These coatings may, for example, be applied by evaporation, sputtering or CVD coating, and may, for example, comprise Al 2 O 3 , SiO 2 , Si 3 N 4 , TiO 2 , ZrO 2 , Ta 2 O 5 , HfO 2 , Si or other materials and combinations of these materials. 
     The layer sequence  200  may additionally comprise a contact layer (not represented in  FIG. 1 ) above the upper cladding layer  250 . Furthermore, a metallization (not represented in  FIG. 1 ) used to electrically contact the semiconductor structure  20  of the edge-emitting semiconductor laser may be arranged on an upper side of the layer sequence  200 . This metallization may extend over the central section  300  and the first edge section  410 , although it may also be restricted to the central section  300 . 
     Further edge-emitting semiconductor lasers will be described below with the aid of  FIGS. 2 to 8 . The further edge-emitting semiconductor lasers respectively have major correspondences with the edge-emitting semiconductor laser  10  of  FIG. 1 . Only the differences of the further edge-emitting semiconductor lasers from the edge-emitting semiconductor laser  10  of  FIG. 1  will therefore respectively be explained below. Components of the further edge-emitting semiconductor lasers that correspond to the components existing in the edge-emitting semiconductor laser  10  of  FIG. 1  are provided with the same references in  FIGS. 2 to 8  as in  FIG. 1 . 
       FIG. 2  shows a schematic sectional side view of the semiconductor structure  20  of an edge-emitting semiconductor laser  11  according to a second example. In the edge-emitting semiconductor laser  11 , the semiconductor structure  20 , in addition to the central section  300  and the first edge section  410  adjacent to the first facet  400 , has a second edge section  510  adjacent to the second facet  500 . In this case, a second offset  530  in the growth direction  201  is formed in the layer sequence  200  between the second edge section  510  and the central section  300 . 
     The second offset  530  of the layer sequence  200  of the semiconductor structure  20  of the edge-emitting semiconductor laser  11 , between the second edge section  510  and the central section  300 , is configured such that the layers  210 ,  220 ,  230 ,  240 ,  250  of the layer sequence  200  lie lower in the growth direction  201  in the second edge section  510  than in the central section  300 . In the second edge section  510 , the upper cladding layer  250  is arranged in the growth direction  201  at the height of the active layer  230  in the central section  300 . Light excited in the central section  300  of the semiconductor structure  20  and guided in the waveguide layers  220 ,  240  is therefore guided at least partially in the upper cladding layer  250  in the second edge section  510 , and therefore cannot be absorbed in the second edge section  510 , or can be absorbed only to a small extent in the second edge section  510 . In the semiconductor structure  20  of the edge-emitting semiconductor laser  11 , therefore, the second facet  500  and the second edge section  510 , which is adjacent to the second facet  500 , also form a nonabsorbing mirror. 
     During the epitaxial growth of the layer sequence  200  of the semiconductor structure  20  of the edge-emitting semiconductor laser  11 , the second offset  530  has been produced by a step  120  formed between the second edge section  510  and the central section  300  on the upper side  101  of the substrate  100 . In the semiconductor structure  20  of the edge-emitting semiconductor laser  11 , the substrate  100  therefore respectively has a step  120  both at the boundary between the first edge section  410  and the central section  300  and at the boundary between the second edge section  510  and the central section  300 . 
     The second edge section  510 , adjacent to the second facet  500 , and the second offset  530  may be configured mirror-symmetrically with respect to the first edge section  410 , adjacent to the first facet  400 , and the first offset  430 . In this case, the width of the second edge section  510 , i.e. the distance of the central section  300  from the second facet  500 , corresponds to the width  440  of the first edge section  410 . Furthermore, in this case, the size of the second offset  530  of the layer sequence  200  in the growth direction  201  in the second edge section  510  corresponds to the size of the first offset  430  of the layer sequence  200  in the first edge section  410 . 
       FIG. 3  shows a schematic sectional side view of the semiconductor structure  20  of an edge-emitting semiconductor laser  12  according to a third example. The edge-emitting semiconductor laser  12  differs from the edge-emitting semiconductor laser  10  of  FIG. 1  in that the first offset  430  of the layer sequence  200  in the first edge section  410  is configured such that the layer sequence  200  lies higher in the growth direction  201  in the first edge section  410  than in the central section  300 . In the first edge section  410 , the lower cladding layer  210  of the layer sequence  200  therefore lies in the growth direction  201  at the height of the active layer  230  in the central section  300 . As an alternative, in the first edge section  410 , the lower waveguide layer  220  could also lie in the growth direction  201  at the height of the active layer  230  in the central section  300 . 
     In the edge-emitting semiconductor laser  12 , light excited in the active layer  230  in the central section  300  of the semiconductor structure  20  and guided in the waveguide layers  220 ,  240  is guided at least partially in the lower cladding layer  210  in the first edge section  410 . The latter has an increased band gap compared to the waveguide layers  220 ,  240  so that absorption of light cannot take place, or can take place only to a small extent, in the first edge section  410 . The first facet  400  and the first edge section  410 , adjacent to the first facet  400 , therefore also form a nonabsorbing mirror in the semiconductor structure  20  of the edge-emitting semiconductor laser  12 . 
     In the semiconductor structure  20  of the edge-emitting semiconductor laser  12 , the substrate  100  also has a step  120  on its upper side  101  between the central section  300  and the first edge section  410 , which step is continued in the layer sequence  200  grown over the upper side  101  of the substrate  100  and causes the first offset  430 . In the semiconductor structure  20  of the edge-emitting semiconductor laser  12 , however, the step  120  on the upper side  101  of the substrate  100  is configured such that the upper side  101  of the substrate  100  lies higher in the growth direction  201  in the first edge section  410  than in the central section  300 . This may have been achieved by a part of the substrate  100  having been removed before the epitaxial growth of the layer sequence  200  in the central section  300  of the substrate  100 , for example, by an etching process, in particular a dry etching process. 
     The semiconductor structure  20  of the edge-emitting semiconductor laser  12  may, in a similar way to the semiconductor structure  20  of the edge-emitting semiconductor laser  11  of  FIG. 2 , also be configured with a second offset  530  in the second edge section  510 , which is adjacent to the second facet  500  so that the second facet  500  and the second edge section  510 , which is adjacent to the second facet  500 , also form a nonabsorbing mirror. In this case, the second edge section  510  and the second offset  530  may, for example, be configured mirror-symmetrically with respect to the first edge section  410  and the first offset  430 . 
       FIG. 4  shows a schematic sectional side view of the semiconductor structure  20  of an edge-emitting semiconductor laser  13  according to a fourth example. The semiconductor structure  20  of the edge-emitting semiconductor laser  13  is configured like the semiconductor structure  20  of the edge-emitting semiconductor laser  12  of  FIG. 3 . 
     In the edge-emitting semiconductor laser  13 , an upper metallization  110  that electrically contacts the edge-emitting semiconductor laser  13  is arranged over the upper cladding layer  250  of the layer sequence  200 . A contact layer (not represented in  FIG. 4 ) could furthermore also be arranged between the upper cladding layer  250  and the upper metallization  110 . The upper metallization  110  extends over the central section  300 , but not over the first edge section  410  of the semiconductor structure  20 . During operation of the edge-emitting semiconductor laser  13 , therefore, electrical current is not conducted, or conducted only to a small extent, in the first edge section  410  through the layer sequence  200  of the semiconductor structure  20 . The effect achieved by this is that light is not excited, or excited only to a small extent, in the first edge section  410  of the semiconductor structure  20 . 
     If the semiconductor structure  20  of the edge-emitting semiconductor laser  13  is configured with a second offset  530  in the second edge section  510 , which is adjacent to the second facet  500 , then it is also possible, for example, for the upper metallization  110  not to extend over the second edge section  510 . 
       FIG. 5  shows a schematic sectional side view of the semiconductor structure  20  of an edge-emitting semiconductor laser  14  according to a fifth example. In the semiconductor structure  20  of the edge-emitting semiconductor laser  14 , the first offset  430  is configured in the layer sequence  200  between the first edge section  410  and the central section  300  such that the layer sequence  200  lies higher in the growth direction  201  in the central section  300  than in the first edge section  410 . 
     In the semiconductor structure  20  of the edge-emitting semiconductor laser  14 , however, the substrate  100  does not have a step on its upper side  101 , but is configured in a planar fashion. Instead, in the semiconductor structure  20  of the edge-emitting semiconductor laser  14 , the layer sequence  200  comprises an additional layer  260 , which is arranged in sections between the upper side  101  of the substrate  100  and the lower cladding layer  210 . In the example represented, this additional layer  260  is present only in the central section  300 , but not in the first edge section  410  so that the additional layer  260  forms a step  270  at the boundary between the central section  300  and the first edge section  410 . The step  270  continues in the layer sequence  200  grown epitaxially over the additional layer  260  and over the upper side  101  of the substrate  100  and, therefore, forms the first offset  430 . 
     The additional layer  260  may initially have been applied onto the entire area, i.e. both in the central section  300  and in the first edge section  410 , onto the upper side  101  of the substrate  100 , for example, likewise by epitaxial growth, before the epitaxial growth of the further layers  210 ,  220 ,  230 ,  240 ,  250 . The additional layer  260  may subsequently have been removed in the first edge section  410 , for example, by an etching process in particular, for example, by a dry etching process or a wet chemical etching process. The remaining layers  210 ,  220 ,  230 ,  240 ,  250  of the layer sequence  200  have subsequently been grown. 
     It is possible to remove the additional layer  260  after application onto the entire area on the upper side  101  of the substrate  100  in the first edge section  410  not fully, but only partially so that the additional layer  260  subsequently has a greater height in the growth direction  201  in the central section  300  than in the first edge section  410 . 
     It is also possible to configure the semiconductor structure  20  of the edge-emitting semiconductor laser  14  with a second offset  530  in the second edge section  510 , which is adjacent to the second facet  500 . To this end, the additional layer  260  is also fully or partially removed in the second edge section  510 , before the remaining layers  210 ,  220 ,  230 ,  240 ,  250  of the layer sequence  200  are grown. 
     The additional layer  260  has doping with the same sign as the doping of the lower cladding layer  210 , for example, n-doping. The additional layer  260  may comprise the same material as the lower cladding layer  210 . 
       FIG. 6  shows a schematic sectional side view of the semiconductor structure  20  of an edge-emitting semiconductor laser  15  according to a sixth example. In the semiconductor structure  20  of the edge-emitting semiconductor laser  15 , the upper side  101  of the substrate  100  is also configured in a planar fashion and without a step  120 . Instead, the additional layer  260 , which forms the step  270  that as the first offset  430  continues in the remaining layer sequence  200  of the semiconductor structure  20 , is also present in sections in the semiconductor structure  20  of the edge-emitting semiconductor laser  15  between the upper side  101  of the substrate  100  and the lower cladding layer  210 . 
     In the semiconductor structure  20  of the edge-emitting semiconductor laser  15 , however, the additional layer  260  is present only in the first edge section  410 , but not in the central section  300 . The first offset  430  is therefore configured in the semiconductor structure  20  of the edge-emitting semiconductor laser  15  such that the layer sequence  200  lies higher in the growth direction  201  in the first edge section  410  than in the central section  300 . If the semiconductor structure  20  of the edge-emitting semiconductor laser  15  is configured with a second offset  530  of the layer sequence  200  in the second edge section  510 , which is adjacent to the second facet  500 , then the additional layer  260  is also present in the second edge section  510 . 
     During production of the semiconductor structure  20  of the edge-emitting semiconductor laser  15 , the additional layer  260  may also initially be arranged over the entire area on the upper side  101  of the substrate  100  in the central section  300  and in the first edge section  410 . The additional layer  260  is subsequently fully or partially removed in the central section  300 . 
     In the semiconductor structure  20  of the edge-emitting semiconductor laser  15 , the additional layer  260  also has doping with the same sign as the doping of the lower cladding layer  210 , for example, n-doping. The additional layer  260  may, for example, comprise the same material as the lower cladding layer  210 . 
       FIG. 7  shows a schematic sectional side view of the semiconductor structure  20  of an edge-emitting semiconductor laser  16  according to a seventh example. The semiconductor structure  20  of the edge-emitting semiconductor laser  16  is configured like the semiconductor structure  20  of the edge-emitting semiconductor laser  15 . In the semiconductor structure  20  of the edge-emitting semiconductor laser  16 , however, the additional layer  260  has either doping with the opposite sign compared to the lower cladding layer  210 , i.e., for example, p-doping or comprises an insulating material. If the additional layer  260  comprises an insulating material, then the additional layer  260  may, for example, be configured as an undoped epitaxial layer, a CVD diamond layer or a dielectric layer. 
     In each case, it is expedient to apply the additional layer  260  by epitaxial growth and form it from the same material system as the remaining layer sequence  200 . The effect achieved by this is that the layer sequence  200  is formed with few defects and in a low-stress manner. In this way, it is possible to substantially avoid an increase in leakage currents at the facets  400 ,  500  and an increase in the absorption at the facets  400 ,  500  so that high facet loading limits can be obtained. Furthermore, a minimization of an undesired fracture rate may be achieved by a low-stress layer sequence  200 . Matching the crystal structure of the additional layer  260  to the crystal structure of the remaining layer sequence  200  may improve the fracture quality at the facets  400 ,  500  so that reduced facet losses and improved performance data can again be obtained. 
     During production of the semiconductor structure  20  of the edge-emitting semiconductor laser  16 , the additional layer  260  may also initially be arranged over the entire area on the upper side  101  of the substrate  100  in the central section  300  and in the first edge section  410 . The additional layer  260  is subsequently removed fully in the central section  300 . 
     The effect achieved as a result of the additional layer  260  having doping with the opposite sign compared to the doping of the lower cladding layer  210 , or comprising an insulating material, is that no current flow, or only a small current flow, takes place through the layer sequence  200  in the first edge section  410  during operation of the edge-emitting semiconductor laser  16 . No light is therefore excited in the first edge section  410  of the semiconductor structure  20  of the edge-emitting semiconductor laser  16  so that the first edge section  410  is heated only to a small extent. 
       FIG. 8  shows a schematic sectional side view of the semiconductor structure  20  of an edge-emitting semiconductor laser  17  according to an eighth example. In the semiconductor structure  20  of the edge-emitting semiconductor laser  17 , the layer sequence  200  has a first offset  430  in the first edge section  410 , which is adjacent to the first facet  400 , and a second offset  530  in the second edge section  510 , which is adjacent to the second facet  500 . The offsets  430 ,  530  are configured such that the layer sequence  200  is arranged lower in the growth direction  201  in the central section  300  than in the first edge section  410  and in the second edge section  510 . It would, however, be possible in the semiconductor structure  20  of the edge-emitting semiconductor laser  17  to provide only the first offset  430  in the first edge section  410  and to omit the second offset  530  in the second edge section  510 . 
     In the semiconductor structure  20  of the edge-emitting semiconductor laser  17 , a first transition section  420  is formed between the first edge section  410  and the central section  300 . Correspondingly, a second transition section  520  is also formed between the second edge section  510  and the central section  300 . The individual layers  210 ,  220 ,  230 ,  240 ,  250  of the layer sequence  200  of the semiconductor structure  20  of the edge-emitting semiconductor laser  17  respectively continue continuously from the central section  300  through the first transition section  420  as far as the first edge section  410 , and from the central section  300  through the second transition section  520  as far as the second edge section  510 . In the transition sections  420 ,  520 , the individual layers  210 ,  220 ,  230 ,  240 ,  250  of the layer sequence  200  are arranged not perpendicularly to the growth direction  201 , but at an angle not equal to 90° with respect to the growth direction  201 . 
     In the semiconductor structure  20  of the edge-emitting semiconductor laser  17 , the substrate  100  does not have a step  120 . Instead, the layer sequence  200  of the semiconductor structure  20  of the edge-emitting semiconductor laser  17  comprises an additional layer  260  arranged in the edge sections  410 ,  510  and in the transition sections  420 ,  520  between the upper side  101  of the substrate and the lower cladding layer  210 . In the central section  300 , the additional layer  260  is fully removed in the semiconductor structure  20  of the edge-emitting semiconductor laser  17 . If the additional layer  260  is configured with doping, the sign of which corresponds to the doping of the lower cladding layer  210 , then a part of the additional layer  260  can also be arranged in the central section  300  between the upper side  101  of the substrate  100  and the lower cladding layer  210 . In this case, the parts of the additional layer  260  arranged in the edge sections  410 ,  510  would have a greater thickness in the growth direction  201  than the part of the additional layer  260  arranged in the central section  300 . 
     In the transition sections  420 ,  520 , the thickness of the additional layer  260  measured in the growth direction  201  continuously increases. In the transition sections  420 ,  520 , the additional layer  260  therefore forms ramps  280  whose upper sides are not arranged parallel to the upper side  101  of the substrate  100 . The upper sides of the ramps  280  have an angle with respect to the upper side  101  of the substrate  100 , which may be 3° to 90°, in particular 10° to 88°, in particular 20° to 80°. In the semiconductor structure  20  of the edge-emitting semiconductor laser  17 , the additional layer  260  therefore does not have a step. Instead, in the semiconductor structure  20  of the edge-emitting semiconductor laser  17 , the additional layer  260  forms the ramp  280 , along which the thickness of the additional layer  260  in the growth direction  201  varies continuously. 
     Alternatively, it is possible to omit the additional layer  260 . Instead, the upper side  101  of the substrate  100  is lowered in the central section  300  so that the upper side  101  of the substrate  100  is arranged lower in the growth direction  201  in the central section  300  than in the edge sections  410 ,  510 . In the transition sections  420 ,  520 , the upper side  101  of the substrate  100  is chamfered such that the height of the upper side  101  of the substrate  100 , measured in the growth direction  201 , varies continuously between the central section  300  and the edge sections  410 ,  510 . The upper side  101  of the substrate  100  therefore forms the ramp  280  in the transition sections  420 ,  520 . 
     Alternatively, the additional layer  260  is configured such that it has a greater thickness in the growth direction  201  in the central section  300  than in the edge sections  410 ,  510 . In the transition sections  420 ,  520 , the thickness of the additional layer  260  varies continuously. In the layer sequence  200  subsequently grown epitaxially over the additional layer  260 , the layers  210 ,  220 ,  230 ,  240 ,  250  then lie higher in the growth direction  201  in the central section  300  than in the edge sections  410 ,  510 . 
     Alternatively, the additional layer  260  is omitted. Instead, the upper side  101  of the substrate  100  is structured such that the upper side  101  of the substrate  100  lies higher in the growth direction  201  in the central section  300  than in the edge sections  410 ,  510 . In the transition sections  420 ,  520 , the height of the upper side  101  of the substrate  100  again varies continuously. The layers  210 ,  220 ,  230 ,  240 ,  250  of the layer sequence  200  grown over the upper side  101  of the substrate  100  in this case also lie higher in the growth direction  201  in the central section  300  than in the edge sections  410 ,  510 . 
     Alternatively, the layer sequence  200  lies higher in the growth direction  201  in the first edge section  410  than in the central section  300 , while it lies lower in the growth direction  201  in the second edge section  510  than in the central section  300 . In yet another example, the situation is reversed. 
     Our lasers and methods have been illustrated and described in more detail by the preferred examples. This disclosure is nevertheless not restricted to the examples disclosed. Rather, other variants may be derived herefrom by those skilled in the art without departing from the protective scope of the disclosure. 
     This application claims priority of DE 10 2015 104 184.7, the subject matter of which is incorporated herein by reference.