Abstract
In an embodiment an edge-emitting semiconductor laser includes a semiconductor layer sequence having a waveguide region with an active layer disposed between a first waveguide layer and a second waveguide layer and a layer system arranged outside the waveguide region configured to reduce facet defects in the waveguide region, wherein the layer system includes one or more layers with the material composition Al.sub.xIn.sub.yGa.sub.1-x-yN with 0≤x≤1, 0≤y<1 and x+y≤1, wherein at least one layer of the layer system includes an aluminum portion x≤0.05 or an indium portion y≥0.02, wherein a layer strain is at least 2 GPa at least in some areas, and wherein the semiconductor layer sequence is based on a nitride compound semiconductor material.
Claims
1.-20. (canceled)
21. An edge-emitting semiconductor laser comprising: a semiconductor layer sequence comprising: a waveguide region with an active layer disposed between a first waveguide layer and a second waveguide layer; and a layer system arranged outside the waveguide region configured to reduce facet defects in the waveguide region, wherein the layer system comprises one or more layers with the material composition Al.sub.xIn.sub.yGa.sub.1-x-yN with 0≤x≤1, 0≤y<1 and x+y≤1, wherein at least one layer of the layer system comprises an aluminum portion x≥0.05 or an indium portion y≥0.02, wherein a layer strain is at least 2 GPa at least in some areas, and wherein the semiconductor layer sequence is based on a nitride compound semiconductor material.
22. The edge-emitting semiconductor laser according to claim 21, wherein the layer system comprises one or more layers having a thickness of at least 10 nm.
23. The edge-emitting semiconductor laser according to claim 21, wherein a distance between the layer system and the active layer is at least 500 nm.
24. The edge-emitting semiconductor laser according to claim 21, wherein a distance between the layer system and the active layer is at least 1 μm.
25. The edge-emitting semiconductor laser according to claim 21, wherein a laser radiation propagating in the waveguide region comprises a maximum intensity I.sub.max, and wherein an intensity of the laser radiation in the layer system is not more than 0.2* I.sub.max.
26. The edge-emitting semiconductor laser according to claim 21, wherein the waveguide region is arranged between an n-type cladding layer and a p-type cladding layer, and wherein the layer system is arranged between a substrate of the edge-emitting semiconductor laser and the n-type cladding layer.
27. The edge-emitting semiconductor laser according to claim 21, wherein the layer system comprises at least one Al.sub.xIn.sub.yGa.sub.1-x-yN layer having an indium content y≥0.03.
28. The edge-emitting semiconductor laser according to claim 21, wherein the layer system comprises at least one Al.sub.xIn.sub.yGa.sub.1-x-yN layer comprising an aluminum portion x≥0.1.
29. The edge-emitting semiconductor laser according to claim 21, wherein the layer system comprises at least one In.sub.yGa.sub.1-yN layer configured to generate a compressive strain and at least one Al.sub.xGa.sub.1-xN layer configured to generate a tensile strain.
30. The edge-emitting semiconductor laser according to claim 29, wherein the In.sub.yGa.sub.1-yN layer and the Al.sub.xGa.sub.1-xN layer are directly adjacent to each other.
31. The edge-emitting semiconductor laser according to claim 21, wherein the layer strain in the layer system is at least regionally larger than in the waveguide region.
32. The edge-emitting semiconductor laser according to claim 21, wherein the layer system comprises at least one interface at which the layer strain changes by more than 2 GPa.
33. The edge-emitting semiconductor laser according to claim 21, wherein the layer system comprises at least one interface at which the layer strain changes from compressive strain to tensile strain or from tensile strain to compressive strain.
34. The edge-emitting semiconductor laser according to claim 21, wherein the layer system comprises a plurality of alternating InGaN layers and AlGaN layers.
35. The edge-emitting semiconductor laser according to claim 21, wherein the layer system comprises at least 3 and at most 100 layers.
36. The edge-emitting semiconductor laser according to claim 21, further comprising a first laser facet and a second laser facet, wherein the first laser facet and the second laser facet do not comprise the facet defects in the waveguide region.
37. The edge-emitting semiconductor laser according to claim 21, further comprising a first laser facet and a second laser facet, wherein the first laser facet or the second laser facet comprises the facet defects in the layer system.
38. The edge-emitting semiconductor laser according to claim 21, wherein the edge-emitting semiconductor laser is a laser bar comprising a plurality of emitters arranged side by side.
39. The edge-emitting semiconductor laser according to claim 21, wherein the layer system is adjacent to a GaN layer, and wherein a bending induced by the entire layer system is zero.
40. An edge-emitting semiconductor laser comprising: a semiconductor layer sequence comprising: a waveguide region with an active layer disposed between a first waveguide layer and a second waveguide layer; and a layer system arranged outside the waveguide region configured to reduce facet defects in the waveguide region, wherein the layer system comprises one or more layers with the material composition Al.sub.xIn.sub.yGa.sub.1-x-yN with 0≤x≤1, 0≤y<1 and x+≤1, wherein at least one layer of the layer system comprises an aluminum portion x≥0.05 or an indium portion y≥0.02, wherein a layer strain is at least 2 GPa at least in some areas, wherein the layer system comprises at least one Al.sub.xIn.sub.yGa.sub.1-x-yN layer comprising a gradient of at least one of the indium portion or the aluminum portion, and wherein the semiconductor layer sequence is based on a nitride compound semiconductor material.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] The edge-emitting semiconductor laser is explained in more detail below by means of exemplary embodiments in connection with FIGS. 1 to 26.
[0035] FIG. 1 shows a schematic representation of a cross-section through an edge-emitting semiconductor laser according to an exemplary embodiment;
[0036] FIGS. 2 to 24 each show a schematic representation of the course of the strain (in each case the lower curve) and the bending B (in each case the upper curve) in the layer system in different exemplary embodiments of the edge-emitting semiconductor laser;
[0037] FIG. 25 shows the course of the intensity I of the laser radiation and the refractive index n in the semiconductor layer sequence in an exemplary embodiment of the edge-emitting semiconductor laser; and
[0038] FIG. 26 shows a schematic representation of a cross-section through an edge-emitting semiconductor laser according to a further exemplary embodiment.
[0039] Components that are the same or have the same effect are each given the same reference signs in the figures. The components shown as well as the proportions of the components among each other are not to be regarded as true to scale.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0040] FIG. 1 illustrates a cross-sectional view of an exemplary embodiment of the edge-emitting semiconductor laser 100. The edge-emitting semiconductor laser 100 comprises a semiconductor layer sequence 10 grown in a growth direction z on a substrate 1.
[0041] The semiconductor layer sequence 10 is based on a nitride compound semiconductor, that is, the semiconductor layers of the semiconductor layer sequence 10 comprise, in particular, Al.sub.xIn.sub.yGa.sub.1-x-yN, wherein 0≤x≤1, 0≤y≤1 and x+y≤1. The substrate 1 is a substrate suitable for growing nitride compound semiconductors, preferably a GaN substrate.
[0042] To generate laser radiation, the edge-emitting semiconductor laser 100 includes an active layer 4, which is preferably formed as a single or multiple quantum well structure. The active layer 4 may comprise several partial layers, in particular a sequence of barrier layers and one or more quantum well layers, which are not shown individually in FIG. 1 for simplicity. The edge-emitting semiconductor laser 100 emits laser radiation perpendicular to the growth direction z, i.e. parallel to the layer plane of the active layer 4.
[0043] The active layer 4 is arranged between a first waveguide layer 3A and a second waveguide layer 3B, wherein the first waveguide layer 3A is adjacent to the active layer 4 at the n-side and the second waveguide layer 3B is adjacent to the active layer 4 at the p-side. The waveguide layers 3A, 3B may each be a single layer or comprise a plurality of partial layers. The first waveguide layer 3A and the second waveguide layer 3B, which are directly adjacent to the active layer 4, each comprise GaN or preferably InGaN. An indium content in the waveguide layers 3A, 3B decreases the band gap and increases the refractive index. In particular, the first and second waveguide layers may comprise In.sub.yGa.sub.1-yN with 0.005≤y≤0.1, preferably In.sub.yGa.sub.1-yN with 0.02≤y≤0.07, and particularly preferably In.sub.yGa.sub.1-yN with 0.0≤y≤0.05.
[0044] The active layer 4 and the waveguide layers 3A, 3B form a waveguide region 3. The waveguide region 3 is arranged between an n-type cladding layer 2 and a p-type cladding layer 6.
[0045] To guide the laser radiation in the waveguide region 3, the n-type cladding layer 2 and the p-type cladding layer 6 comprise a lower refractive index than the waveguide layers 3A, 3B. This is realized, for example, by the cladding layers 2, 6 comprising a higher aluminum content and/or lower indium content than the waveguide layers 3A, 3B, at least in some areas, resulting in a larger electronic bandgap and a lower refractive index. The n-type cladding layer 2 and the p-type cladding layer 6 may each be a single layer or comprise a plurality of partial layers.
[0046] In the exemplary embodiment of FIG. 1, an optional electron barrier layer 5 is arranged between the second waveguide layer 3B of the p-type cladding layer 6. The electron barrier layer 5 preferably comprises a larger aluminum content and, accordingly, an even larger band gap than the p-type cladding layer 6. In particular, the electron barrier layer 5 may comprise Al.sub.zGa.sub.1-zN, wherein the aluminum content z is between 0.05 and 0.4, preferably between 0.1 and 0.3, and particularly preferably between 0.15 and 0.25. The electron barrier layer 5 comprises a larger band gap Eg than the adjacent second waveguide layer 3B. This prevents electrons from leaving the waveguide region 3. Furthermore, the large band gap results in a low refractive index, which is advantageously small compared to the waveguide layers 3A, 3B. This improves waveguiding in the waveguide region 3.
[0047] The p-type cladding layer 6 is followed by a p-contact layer 7 on the side facing away from the active layer 4. The p-contact layer 7 may in particular be a GaN layer or an InGaN layer. The p-contact layer 7 is a p-doped layer, which is advantageously highly doped. The dopant concentration in the p-type cladding layer 7 is advantageously at least 5*10.sup.19 cm.sup.−3, preferably at least 1*10.sup.2 cm.sup.−3. The p-type cladding layer 7 can differ from the p-type cladding layer 6 in particular in that it comprises a higher dopant concentration.
[0048] A p-type connection layer 8 is arranged above the p-contact layer 7. Furthermore, the edge-emitting semiconductor laser 100 comprises an n-type connection layer 9, for example on a back side of the substrate 1. The p-type connection layer 8 and the n-type connection layer 9 may comprise, for example, a metal or a metal alloy.
[0049] The semiconductor layer sequence 10 includes a layer system 20 which is intended to reduce or preferably completely avoid facet defects in the waveguide region 3. For this purpose, the layer system 20 is arranged outside the waveguide region 3. In the example of FIG. 1, the layer system 20 is arranged between the substrate 1, which is for example a GaN substrate, and the n-type cladding layer 2. Strains are generated in the layer system 20 by varying the material composition, which are suitable to prevent any facet defects that may occur from propagating into adjacent regions of the semiconductor layer sequence 10. The layer system 20 takes advantage of the knowledge that facet defects occur or propagate at interfaces that comprise high strains. In particular, a strain greater than 2 GPa is generated in the layer system 20 by means of the material composition.
[0050] Therefore, if a facet defect occurs during a mechanical strain on the semiconductor layer sequence 10, which may occur in particular during the formation of the laser facets by scribing and breaking, it will most likely occur at an interface with high strain in the layer system 20 and/or may be redirected at such an interface with high strain parallel to the interface. Therefore, selectively building up layer strains outside the waveguide region 3 in the layer system 20 can advantageously avoid facet defects in the waveguide region 3.
[0051] In the exemplary embodiment of FIG. 1, the layer system comprises an In.sub.yGa.sub.1-yN layer 21 following the GaN substrate 1 and an Al.sub.xG.sub.1-xN layer 22. The In.sub.yGa.sub.1-yN layer 21 and the Al.sub.xGa.sub.1-xN layer 22 are each formed as gradient layers, wherein the indium content y in the growth direction z in the In.sub.yGa.sub.1-yN layer 21 increases from y=0 to y=0.05, and wherein the aluminum content x in the growth direction in the Al.sub.xGa.sub.1-xN layer 22 decreases from x=0.18 to x=0.
[0052] The strain caused by the material composition in the layer system 20, as well as a bending B resulting from such strain, are shown in FIG. 2 as a function of a coordinate z extending in the growth direction. In the diagram of FIG. 2 as well as in the following diagrams, the first 100 nm and the last 100 nm of the diagram each relate to a region outside the layer system 20. In FIG. 2, therefore, the region between z=100 nm and z=500 nm represents the region of the layer system 20.
[0053] In the layer system 20 of FIG. 2, the In.sub.yGa.sub.1-yN gradient layer 21 is about 200 nm thick, wherein the indium content, which increases in the direction of growth, causes increasing compressive strain and increasing bending B. At the interface 23 to the Al.sub.xGa.sub.1-xN layer 22, which is also about 200 nm thick, the high aluminum content x=0.18 causes a change to a tensile strain. The strain and the bending B then decrease again in the growth direction with the falling aluminum content in such a way that after the Al.sub.xGa.sub.1-xN layer 22 has grown, a strain=0 and bending B=0 result.
[0054] In the layer system, doping of the semiconductor layers 21, 22 can take place in the region of the interface 23 between the adjacent layers 21, 22, for example with Si, Ge, C, O or Mg. A thin doped region at the interface 23, also called a doping spike, can avoid a possible electric voltage drop due to piezoelectric fields at the interface 23.
[0055] In general, an indium-containing layer 21 can be used to create a compressive layer strain, and an aluminum-containing layer 22 can be used to create a tensile layer strain. Furthermore, a doping can be used to generate or enhance a layer strain, for example a Si doping can generate a tensile layer strain.
[0056] FIG. 3 shows the variation of strain and bending B for another example of the layer system. The layer system comprises an In.sub.yGa.sub.1-yN gradient layer 21 following the GaN substrate 1, which is 200 nm thick, wherein the indium fraction increases from y=0 to y=0.05 in the growth direction. An Al.sub.xGa.sub.1-xN gradient layer 22 is arranged on top of the In.sub.yGa.sub.1-yN gradient layer 21, which is 730 nm thick, wherein the aluminum fraction decreases from x=0.05 to x=0 in the growth direction. The highest strain is present at the interface 23 of layers 21, 22, wherein the total strain is zero.
[0057] FIG. 4 shows the variation of strain and bending B for another example of the layer system. The layer system comprises an In.sub.yGa.sub.1-yN gradient layer 21 following the GaN substrate 1, which is 200 nm thick, wherein the indium fraction increases from y=0 to y=0.05 in the growth direction. An Al.sub.xGa.sub.1-xN layer 22 is arranged on the In.sub.yGa.sub.1-yN gradient layer 21, which is 72 nm thick, wherein the aluminum fraction is x=0.25. The highest strain is present at the interface 23 of layers 21, 22, wherein the total strain is zero.
[0058] FIG. 5 shows the variation of strain and bending B for another example of the layer system. The layer system comprises an In.sub.yGa.sub.1-yN gradient layer 21 following the GaN substrate 1, which is 200 nm thick, wherein the indium fraction drops from y=0.05 to y=0 in the growth direction. An Al.sub.xGa.sub.1-xN gradient layer 22 is arranged on top of the In.sub.yGa.sub.1-yN gradient layer 21, which is 200 nm thick, wherein the aluminum content increases from x=0 to x=0.18 in the growth direction. At the interface 23 between layers 21, 22, the sign of the layer strain changes, i.e., the layer strain changes from compressive to tensile. The total strain is zero.
[0059] FIG. 6 shows the variation of strain and bending B for another example of the layer system. The layer system comprises an Al.sub.xGa.sub.1-xN gradient layer 22 following the GaN substrate 1, which is 200 nm thick, wherein the aluminum fraction drops from x=0.18 to x=0 in the growth direction. The highest strain is present at the interface 23 between the substrate 1 and the Al.sub.xGa.sub.1-xN gradient layer 22. In contrast to the previous exemplary embodiments, the total strain of the layer system is not zero, rather the layer system as a whole is tensile strained. Such a tensile total strain can be advantageous when the laser facets are broken from the back side.
[0060] FIG. 7 shows the course of the strain and the bending B for another example of the layer system. The layer system comprises an Al.sub.xGa.sub.1-xN gradient layer 22 following the GaN substrate 1, which is 200 nm thick, wherein the aluminum fraction increases from x=0 to x=0.18 in the growth direction. The highest strain is present at an interface 23 of the Al.sub.xGa.sub.1-xN gradient layer 22 facing away from the substrate. As in the previous example, the layer system as a whole is tensile strained. Such an overall tensile strain can be advantageous when the laser facets are broken from the back side.
[0061] FIG. 8 shows the course of the strain and the bending B in another example of the layer system. The layer system comprises an Al.sub.xGa.sub.1-xN gradient layer 22 following the GaN substrate 1, which is 150 nm thick, wherein the aluminum fraction increases from x=0 to x=0.18 in the growth direction. An In.sub.yGa.sub.1-yN gradient layer 21 is arranged on the Al.sub.xGa.sub.1-xN gradient layer 22, which is 50 nm thick, wherein the indium fraction decreases from y=0.05 to y=0 in the growth direction. The highest strain is present at the interface 23 of layers 21, 22, wherein the layer system as a whole is tensile strained, as in the two previous examples.
[0062] FIG. 9 shows the course of the strain and the bending B for another example of the layer system. The layer system comprises an In.sub.yGa.sub.1-yN gradient layer 21 following the GaN substrate 1, which is 50 nm thick, wherein the indium fraction increases from y=0 to y=0.07 in the growth direction. An Al.sub.xGa.sub.1-xN gradient layer 22 is arranged on top of the In.sub.yGa.sub.1-yN gradient layer 21, which is 150 nm thick, wherein the aluminum fraction decreases from x=0.2 to x=0 in the growth direction. The highest strain is present at the interface 23 of layers 21, 22, wherein the layer system as a whole is tensile strained, as in the three previous examples.
[0063] FIG. 10 shows the course of the strain and the bending B for another example of the layer system. The layer system comprises an In.sub.yGa.sub.1-yN gradient layer 21A following the GaN substrate 1, which is 100 nm thick, wherein the indium fraction increases from y=0 to y=0.07 in the growth direction. On top of the In.sub.yGa.sub.1-yN gradient layer 21A, another one In.sub.yGa.sub.1-yN gradient layer 21B is arranged, which is 100 nm thick, wherein the indium content decreases from y=0.07 to y=0 in the growth direction. In contrast to the previous exemplary embodiments, the layer system is overall compressively strained. Such an overall compressive strain can be advantageous when the laser facets are broken from the front side.
[0064] FIG. 11 shows the course of the strain and the bending B in another example of the layer system. The layer system comprises an In.sub.yGa.sub.1-yN gradient layer 21A following the GaN substrate 1, which is 100 nm thick, wherein the indium fraction increases from y=0 to y=0.04 in the growth direction. This is followed by an In.sub.yGa.sub.1-yN layer 21B, which is 100 nm thick, with a constant indium fraction y=0.04. On top of the In.sub.yGa.sub.1-yN layer 21B, an In.sub.yGa.sub.1-yN gradient layer 21C is arranged, which is 100 nm thick, wherein the indium fraction decreases from y=0.04 to y=0 in the growth direction. As in the previous example, the layer system as a whole is compressively strained.
[0065] FIG. 12 shows the variation of strain and bending B for another example of the layer system. The layer system comprises an In.sub.yGa.sub.1-yN gradient layer 21 following the GaN substrate 1, which is 200 nm thick, wherein the indium fraction decreases from y=0.05 to 7=0 in the growth direction. The highest strain is present at the interface 23 between the substrate 1 and the In.sub.yGa.sub.1-yN gradient layer 21. As in the previous example, the layer system as a whole is compressively strained.
[0066] FIGS. 13, 14 and 15 show the variation of strain and bending B in other examples of the layer system, each comprising a superlattice structure of alternating In.sub.yGa.sub.1-yN layers 21 and Al.sub.xGa.sub.1-xN layers 22. In the example of FIG. 13, the layer system has alternating In.sub.yGa.sub.1-yN layers 21, which are 20 nm thick and comprise an indium portion y=0.05, and Al.sub.xGa.sub.1-xN layers 22, which are 20 nm thick and comprise an aluminum portion x=0.15. In the example of FIG. 14, the layer system alternately comprises In.sub.yGa.sub.1-yN gradient layers 21, which are 25 nm thick and comprise an indium fraction decreasing from y=0.08 to 7=0, and Al.sub.xGa.sub.1-xN gradient layers 22, which are 25 nm thick and comprise an aluminum fraction increasing from x=0 to x=0.2. In the example of FIG. 15, the layer system alternately comprises In.sub.yGa.sub.1-yN gradient layers 21, which are 25 nm thick and comprise an indium fraction decreasing from y=0.04 to y=0, and Al.sub.xGa.sub.1-xN gradient layers 22, which are 25 nm thick and comprise an aluminum fraction increasing from x=0 to x=0.22. Superlattice structures have the advantage of comprising a large number of interfaces that can prevent potential facet defects from propagating.
[0067] The following FIGS. 16, 17 and 18 show the course of the strain and the bending B in further examples of the layer system, in which in each case two interfaces with high strain are close to each other, so that facet defects in a defined area as small as possible are prevented from propagating.
[0068] In the example of FIG. 16, the layer system, starting from the GaN substrate 1, comprises a 50 nm thick In.sub.yGa.sub.1-yN gradient layer 21A with an indium fraction increasing in the growth direction from y=0 to y=0.05, a 30 nm thick In.sub.yGa.sub.1-yN gradient layer 21B having an indium content decreasing in the growth direction from y=0.05 to y=0, a 30 nm thick Al.sub.xGa.sub.1-xN gradient layer 22A having an aluminum content increasing in the growth direction from x=0 to x=0, 22 increasing aluminum content, a 30 nm thick Al.sub.xGa.sub.1-xN gradient layer 22B with aluminum content decreasing in the growth direction from x=0.22 to x=0, a 30 nm thick In.sub.yGa.sub.1-yN gradient layer 21C having an indium portion increasing in the growth direction from y=0 to y=0.05, and a 50 nm thick In.sub.yGa.sub.1-yN gradient layer 21D having an indium portion decreasing in the growth direction from y=0.05 to y=0.
[0069] In the example of FIG. 17, starting from the GaN substrate 1, the layer system comprises a 50 nm thick In.sub.yGa.sub.1-yN gradient layer 21A with an indium fraction increasing in the growth direction from y=0 to y=0.05, a 10 nm thick Al.sub.xGa.sub.1-xN layer 22 with an aluminum fraction x=0.25 and a 50 nm thick In.sub.yGa.sub.1-yN gradient layer 21B with an indium fraction decreasing in the growth direction from y=0.05 to y=0.
[0070] In the example of FIG. 18, starting from the GaN substrate 1, the layer system comprises a 100 nm thick Al.sub.xGa.sub.1-xN gradient layer 22A with an aluminum portion increasing in the growth direction from x=0 to x=0.12, a 30 nm thick In.sub.yGa.sub.1-yN layer 21 with an indium portion y=0.05, and a 100 nm thick Al.sub.xGa.sub.1-xN gradient layer 22B with an aluminum portion decreasing in the growth direction from x=0.12 to x=0.
[0071] The following FIGS. 19, 20 and 21 show the variation of strain and bending B for further examples of the layer system, each comprising alternating Al.sub.xGa.sub.1-xN layers 22 and In.sub.yGa.sub.1-yN layers 21. In the example of FIG. 19, the aluminum content of the Al.sub.xGa.sub.1-xN layers 22 decreases from layer to layer, while the In.sub.yGa.sub.1-yN layers 21 each comprise the same indium content. In the example of FIG. 20, the aluminum content of the Al.sub.xGa.sub.1-xN layers 22 decreases from layer to layer, and the indium content of the In.sub.yGa.sub.1-yN layers 21 increases from layer to layer. In the example of FIG. 21, both the aluminum content of the Al.sub.xGa.sub.1-xN layers 22 and the indium content of the In.sub.yGa.sub.1-yN layers 21 decrease from layer to layer.
[0072] FIGS. 22, 23 and 24 show the variation of strain and bending B in further examples of the layer system, each comprising alternating Al.sub.xGa.sub.1-xN layers 22 and In.sub.yGa.sub.1-yN layers 21. In these examples, the Al.sub.xGa.sub.1-xN layers 22 each comprise the same aluminum content and the In.sub.yGa.sub.1-yN layers 21 each comprise the same indium content. In the layer systems, however, the thickness of the Al.sub.xGa.sub.1-xN layers 22 and In.sub.yGa.sub.1-yN layers 21 varies.
[0073] FIG. 25 shows schematically the course of the intensity I of the laser radiation and the refractive index n (both in arbitrary units) in an exemplary embodiment of the edge-emitting semiconductor laser as a function of a depth t measured from the surface. The laser radiation comprises the maximum intensity in the active region 4. At the location of the layer system 20, the intensity is less than 20%, preferably less than 10% and particularly preferably only less than 5% of the maximum intensity. This can be achieved in particular by a sufficiently large distance between the layer system 20 and the active layer 4, wherein the distance is at least 500 nm, preferably at least 1 μm.
[0074] FIG. 26 schematically shows another exemplary embodiment of the edge-emitting semiconductor laser 100 in cross-section. The arranging of the layers of the semiconductor layer sequence lo corresponds to the example of FIG. 1 and is therefore not explained in detail again. The difference from the example of FIG. 1 is that the edge-emitting semiconductor laser 100 shown here is a laser bar which comprises a plurality of emitters arranged side by side. A plurality of side-by-side ridge waveguides 11 are formed on the surface of the laser bar, on each of which a p-type connection layer 8 is arranged. The p-type connection layers 8 each contact the upper side of the ridge waveguides ii and are otherwise electrically isolated from the semiconductor layer sequence lo by a passivation layer 12. The layer system 20 for reducing facet defects in the waveguide region 3 may be arranged between the substrate 1 and the n-type cladding layer 2, for example, as in the exemplary embodiment of FIG. 1. The layer system 20 for reducing facet defects is particularly advantageous in a laser bar, since facet defects of a single emitter may lead to failure of the entire laser bar.
[0075] The invention is not limited by the description based on the exemplary embodiments. Rather, the invention encompasses any new feature as well as any combination of features, which particularly includes any combination of features in the claims, even if that feature or combination itself is not explicitly specified in the claims or exemplary embodiments.
