EDGE-EMITTING SEMICONDUCTOR LASER DIODES AND METHOD FOR PRODUCING A PLURALITY OF EDGE-EMITTING SEMICONDUCTOR LASER DIODES

Abstract

The invention relates to an edge-emitting semiconductor laser diode, including the following features: an epitaxial semiconductor layer stack including an active one, in which during operation electromagnetic radiation is generated, wherein the epitaxial semiconductor layer stack has at least one facet which laterally delimits the epitaxial semiconductor layer stack, and the facet has at least one first partial surface and at least one second partial surface which have reflectivities differing from one another for the electromagnetic radiation generated in the active zone. The invention also relates to methods for producing a plurality of edge-emitting semiconductor laser diodes.

Claims

1. An edge emitting semiconductor laser diode comprising: an epitaxial semiconductor layer stack comprising an active zone, in which electromagnetic radiation is generated during operation, wherein the epitaxial semiconductor layer stack has at least one facet, which laterally delimits the epitaxial semiconductor layer stack, the facet has at least a first partial surface and at least a second partial surface, which have different reflectivities from one another for the electromagnetic radiation generated in the active zone, and the first partial surface amplifies a desired mode of the electromagnetic laser radiation, and the second partial surface at least attenuates undesired modes of the electromagnetic laser radiation.

2. The edge emitting semiconductor laser diode according to claim 1, wherein the electromagnetic radiation generated in the active zone is formed in a resonator into electromagnetic laser radiation comprising a plurality of modes.

3. The edge-emitting semiconductor laser diode according to claim 1, wherein the first partial surface and the second partial surface have different roughnesses.

4. The edge emitting semiconductor laser diode according to claim 1, wherein the first partial surface is formed tilted by a first vertical angle relative to a vertical main surface of the epitaxial semiconductor layer stack, wherein the vertical main surface is perpendicular to a longitudinal direction, and/or the second partial surface is tilted by a second vertical angle relative to the vertical main surface of the epitaxial semiconductor layer stack.

5. The edge emitting semiconductor laser diode according to claim 1, wherein the first partial surface is tilted by a first lateral angle relative to the vertical main surface of the epitaxial semiconductor layer stack, and/or the second partial surface is tilted by a second lateral angle relative to the vertical main surface of the epitaxial semiconductor layer stack.

6. The edge-emitting semiconductor laser diode according to claim 1, wherein the first partial surface covers a radiation exit region of the facet.

7. The edge emitting semiconductor laser diode according to claim 1, wherein the first partial surface covers a radiation exit region of the facet, and the first partial surface is arranged between two second partial surfaces, which have a lower reflectivity for the electromagnetic radiation of the active zone than the first partial surface.

8. The edge emitting semiconductor laser diode according to claim 1, which has a ridge waveguide.

9. The edge emitting semiconductor laser diode according to claim 1, wherein the facet has further partial surfaces with at least partially different reflectivities for the electromagnetic radiation generated in the active zone.

10. The edge-emitting semiconductor laser diode according to claim 1, wherein the facet has a plurality of partial surfaces each of which is tilted by a lateral angle relative to the vertical main surface of the epitaxial semiconductor layer stack and forms at least one cut-out and/or at least one protrusion in the facet.

11. An array comprising at least two edge-emitting semiconductor laser diodes according to claim 1.

12. A method of manufacturing a plurality of edge-emitting semiconductor laser diodes comprising: providing an epitaxial semiconductor layer sequence with an active region, which generates electromagnetic radiation during operation, generating one or more trenches in the epitaxial semiconductor layer sequence, and generating at least a first partial surface and at least a second partial surface on a side surface of the trench, wherein the first partial surface and the second partial surface have different reflectivities from one another for the electromagnetic radiation generated in the active region, and the first partial surface amplifies a desired mode of the electromagnetic laser radiation, and the second partial surface at least attenuates undesired modes of the electromagnetic laser radiation.

13. The method according to claim 12, wherein the trenches are generated by a dry etching process so that the side surfaces of the trenches have a vertical angle tilted to a vertical main surface of the epitaxial semiconductor layer sequence, the vertical main surface being perpendicular to a longitudinal direction, and the first partial surface or the second partial surface is generated by a wet chemical method using a mask, wherein the first partial surface and the second partial surface have different roughnesses.

14. The method according to claim 13, wherein the partial surface generated by the wet chemical method has a lower roughness than the other partial surface.

15. The method according to claim 12, wherein the trenches are generated with a dry etching process using a mask, so that the first partial surface encloses a first vertical angle with the vertical main surface and/or the second partial surface encloses a second vertical angle with the vertical main surface.

16. The method according to 12, in which the trenches are generated with a dry etching process using at least one mask, so that the first partial surface encloses a first lateral angle with the vertical main surface and/or the second partial surface encloses a second lateral angle with the vertical main surface.

17. The method according to claim 15, wherein the mask has at least two mask layers, which have different selectivities for the dry etching process.

18. A method of manufacturing a plurality of edge-emitting semiconductor laser diodes comprising: providing an epitaxial semiconductor layer sequence with an active region, which generates electromagnetic radiation during operation, generating a plurality of structural elements in the epitaxial semiconductor layer sequence, wherein a side surface of a structural element at least partially forms a first partial surface of a facet of a finished semiconductor laser diode, singulating the semiconductor layer sequence to form a plurality of edge-emitting semiconductor laser diodes, so that at least a second partial surface of the facet of the finished semiconductor laser diode is formed, wherein the first partial surface and the second partial surface have different reflectivities from one another for the electromagnetic radiation generated in the active region, and the first partial surface amplifies a desired mode of the electromagnetic laser radiation, and the second partial surface at least attenuates undesired modes of the electromagnetic laser radiation.

19. The method according to claim 18, wherein the first partial surface has a greater roughness than the second partial surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0080] The schematic sectional views of FIGS. 1 to 5 show different stages of a method of manufacturing a plurality of semiconductor laser diodes according to an exemplary embodiment.

[0081] FIG. 6 shows a schematic top view of a facet of an edge-emitting semiconductor laser diode according to an exemplary embodiment.

[0082] The schematic views of FIGS. 7 to 9 illustrate the directions in space and areas of the edge-emitting semiconductor laser diode in more detail.

[0083] The schematic sectional view of FIG. 10 shows a stage of a method of manufacturing a plurality of semiconductor laser diodes according to a further exemplary embodiment.

[0084] The schematic sectional view of FIG. 11 shows a stage of a method of manufacturing a plurality of semiconductor laser diodes according to a further exemplary embodiment.

[0085] The schematic top views of FIGS. 12 and 13 show different stages of a method of manufacturing a plurality of semiconductor laser diodes according to a further exemplary embodiment.

[0086] FIGS. 14 to 32 show schematic representations of edge-emitting semiconductor laser diodes according to various exemplary embodiments.

[0087] FIG. 33 shows an example of a scanning electron microscope image of a facet of a semiconductor laser diode.

[0088] FIGS. 34 to 36 show schematic views of edge-emitting semiconductor laser diodes according to further exemplary embodiments.

[0089] FIGS. 37 and 38 show schematic representations of an array with a plurality of edge-emitting semiconductor laser diodes according to an exemplary embodiment.

DETAILED DESCRIPTION

[0090] Elements that are identical, similar or have the same effect are marked with the same references in the figures. The figures and the proportions of the elements shown in the figures are not to be regarded as true to scale. Rather, individual elements, in particular layer thicknesses, may be shown in exaggerated size for better visualization and/or understanding.

[0091] In the method according to the exemplary embodiment of FIGS. 1 to 5, an epitaxial semiconductor layer sequence 1 is first provided, which has an active region 2 that is suitable for generating electromagnetic radiation during operation (not shown). The epitaxial semiconductor layer sequence 1 is provided in the present case in the form of a wafer and has a main surface 3.

[0092] A plurality of trenches 4 is provided in the epitaxial semiconductor layer sequence 1. For reasons of clarity, FIG. 1 only shows a section of the epitaxial semiconductor layer sequence 1 with a single trench 4.

[0093] The trenches 4 are preferably formed in the same way. The trenches 4 are particularly preferably arranged parallel to one another in the epitaxial semiconductor layer sequence 1.

[0094] The trench 4 does not completely penetrate the epitaxial semiconductor layer sequence 1 in the present case, but breaks through the active region 2. In other words, the wafer is still designed to be completely continuous in the epitaxial semiconductor layer sequence 1 after the trenches 4 have been generated.

[0095] The trench 4 has two opposite side surfaces 5. In the present case, the trenches 4 in the epitaxial semiconductor layer sequence 1 are generated by a plasma etching process. In this process, the side surfaces 5 of the trenches 4 are formed oblique to a vertical main surface 6 of the epitaxial semiconductor layer sequence 1. In addition, the side surfaces 5 of the trenches 4 have a comparatively high roughness due to the plasma etching process.

[0096] In a next step, a mask 7 is applied to the side surfaces 5 of the trenches 4 (FIGS. 2 and 3). As the top view of the side surface 5 of the trench 4 of FIG. 3 shows, the mask 7 is only applied in places to the side surface 5 of the trench 4, so that an region 8 of the side surface 5 is freely accessible.

[0097] In the present case, protrusions are already arranged in the main surface 3 of the epitaxial semiconductor layer sequence 1, which serve as the ridge waveguides 9 in the finished semiconductor laser diodes. In particular, regions 8 of the side surfaces 5 are not covered by the mask 7, which are arranged below the ridge waveguide 9 as seen from the main surface 3.

[0098] The mask 7 can, for example, be generated using a structured photoresist mask and a subsequent lift-off method. Here, the material of the mask is first applied over the entire surface of a structured photoresist mask on the side surface 5 of the trench 44. The photoresist mask is then removed so that the inverse structure of the photoresist mask is transferred to the material of the mask. Furthermore, it is also possible to apply a structured photoresist mask to a mask layer applied over the entire surface of the side surface 5 of the trench 4 and to actively structure the mask layer, for example by means of an etching process.

[0099] In a next step, the side surfaces 5 of the trenches 4 are smoothed with a wet chemical method, for example using KOH, TMAH, NH.sub.3, NaOH as the etching medium, whereby the regions 8 of the side surfaces 5 not covered by the mask 7 are simultaneously formed parallel to the vertical main surface 6 of the epitaxial semiconductor layer sequence 1 (FIG. 4). Thus, first partial surfaces 10 are formed on the side surfaces 5 of the trenches 4, which have a lower roughness than second partial surfaces 11. FIG. 5 shows a section through a partial surface with an increased roughness.

[0100] Finally, the semiconductor laser diodes are singulated along the trenches, for example by breaking, so that a plurality of edge-emitting semiconductor laser diodes are created.

[0101] FIG. 6 shows a schematic top view of a facet 12 of an edge-emitting semiconductor laser diode as it can be produced using the method according to the exemplary embodiment of FIGS. 1 to 5.

[0102] The edge-emitting semiconductor laser diode according to the exemplary embodiment of FIG. 6 has a facet 12 with a first partial surface 10 and two second partial surfaces 11, wherein the first partial surface 10 is arranged between the second partial surfaces 11. In the present case, the first partial surface 10 has a lower roughness than the two second partial surfaces 11, which have the same roughness in the present case.

[0103] In the present case, the first partial surface 10 covers a radiation exit region 13 of the facet, from which electromagnetic laser radiation generated during operation emerges from the semiconductor laser diode. In particular, the edge-emitting semiconductor laser diode according to the exemplary embodiment of FIG. 6 has a ridge waveguide 9, under which the radiation exit region 13 of the facet 12 is arranged.

[0104] The schematic diagrams in FIGS. 7 and 9 are used to explain the terms vertical main surface 6, longitudinal direction R.sub.L, stacking direction R.sub.S and vertical angle .sub.W and lateral angle .sub.L in more detail.

[0105] The semiconductor laser diode according to FIG. 7 has an epitaxial semiconductor layer stack 14 with an active zone 15. The epitaxial semiconductor layer stack 14 has a plurality of epitaxial semiconductor layers 16 which are stacked on top of each other in a stacking direction R.sub.S.

[0106] The epitaxial semiconductor layer stack 14 is delimited by two facets 12, which form a resonator 17. A longitudinal direction R.sub.L extends from one facet 12 to the opposite other facet 12 parallel to an optical axis 18 of the resonator 17.

[0107] The two facets 12 are further connected to each other by side surfaces 19 of the epitaxial semiconductor layer stack 16, which extend parallel to the longitudinal direction R.sub.L. Furthermore, a ridge waveguide 9 extends along the longitudinal direction R.sub.L between the two facets 12.

[0108] A vertical main surface 6 of the epitaxial semiconductor layer stack runs parallel to the stacking direction R.sub.S and is perpendicular to the longitudinal direction R.sub.L.

[0109] FIG. 8 shows a top view of a main surface 3 of the epitaxial semiconductor layer stack 14 with the ridge waveguide 9. A second partial surface 11 of the facet 12 encloses a lateral angle .sub.L with the vertical main surface 6, while a first partial surface 10 of the facet 12 runs parallel to the vertical main surface 6.

[0110] FIG. 9 shows a top view of a side surface 19 of the epitaxial semiconductor layer stack 14, with a second partial surface 11 of the facet 12 forming a vertical angle .sub.W with the vertical main surface 6.

[0111] In the method according to the exemplary embodiment of FIG. 10, a mask 7 is applied to a main surface 3 of the epitaxial semiconductor layer sequence 1. In the present case, the mask 7 comprises two different mask layers 7, 7, which are arranged laterally next to one another and cover different regions of the main surface 3 of the epitaxial semiconductor layer sequence 1. In other words, the mask is structured. The mask layers 7, 7 are formed, for example, from different materials. For example, metals, oxides, or photoresist are suitable materials for the mask layers 7, 7. The two mask layers 7, 7 of the mask 7 can have different selectivities for a subsequent dry etching process.

[0112] In a subsequent step, which is not shown here, a plurality of trenches 4 is generated in the epitaxial semiconductor layer sequence 3 using a dry etching process such as plasma etching. Due to the structuring of the mask 7, trenches 4 with side surfaces 5 with different lateral angles di are formed with a vertical main surface 6 in the dry etching process.

[0113] In a subsequent step, the areas of the side surfaces 5 that include different lateral angles .sub.L with the vertical main surface 6 are wet chemically etched so that regions that include a smaller lateral angle .sub.L with the vertical main surface 6 have a lower roughness, as they are smoothed more than regions that include a larger lateral angle .sub.L with the vertical main surface 6, especially if the epitaxial semiconductor layer sequence 1 is based on GaN. The reason for this is the deviation of the tilted plane from an m-plane of the GaN crystal.

[0114] For example, areas of the side surface 5 that are strongly smoothed have lateral angles .sub.L with the vertical main surface 6 not greater than +/6, while areas that are poorly smoothed include a lateral angle .sub.L of at least +/8, preferably of at least +/10 with the vertical main surface 6.

[0115] In the method according to the exemplary embodiment of FIG. 11, a mask 7 with two different mask layers 7, 7, which have different selectivities for a dry etching process, is used as in the method according to the exemplary embodiment of FIG. 10. However, in the present method, the two mask layers 7, 7 are not only arranged laterally next to each other, but also on top of each other in a stacking direction R.sub.S of the semiconductor layer sequence 1. Thus, in the dry etching process, trenches 4 are generated whose side surfaces 5 have partial surfaces 10, 11 that enclose different vertical angles W with a vertical main surface 6.

[0116] In this exemplary embodiment, the side surfaces 5 of the trenches 4 are also smoothed by a wet chemical method in which partial surfaces 10, 11, which include a vertical angle .sub.W not greater than +/6 with the vertical main surface 6, are smoothed strongly and partial surfaces 10, 11, which include a vertical angle .sub.W greater than +/8, preferably greater than +/10 with the vertical main surface 6, are smoothed weakly or not at all.

[0117] In the method according to the exemplary embodiment of FIGS. 12 and 13, a plurality of structural elements 20 are first introduced into a main surface 3 of the epitaxial semiconductor layer sequence 1, for example by plasma etching (FIG. 12). For reasons of clarity, FIGS. 12 and 13 show only a section of the epitaxial semiconductor layer sequence 1, which later forms two semiconductor laser diodes. Therefore, FIG. 12, in particular, shows a single structural element.

[0118] For example, the structural elements 20 are arranged along a straight line G, which is perpendicular to a stacking direction R.sub.S of the epitaxial semiconductor layer sequence 1 and to a longitudinal direction R.sub.L.

[0119] In a next step, the facets 12 are generated by singulating the edge-emitting semiconductor laser diodes along separation lines that run through the cut-outs 20 by scribing and breaking.

[0120] The semiconductor laser diode according to the exemplary embodiment of FIGS. 14 and 15 has a facet 12 with a first partial surface 10 and two second partial surfaces 12. The first partial surface 10 is arranged between the two second partial surfaces 12 and covers a radiation exit region 13 of the facet 12. In the present case, the first partial surface 10 has a smaller first vertical angle .sub.W1 with a vertical main surface 6 than the two second partial surfaces 12, which each include a larger second vertical angle .sub.W2 with the vertical main surface 6.

[0121] Furthermore, the first partial surface 10 has a lower roughness and thus a greater reflectivity for the electromagnetic radiation generated in an active zone 15 of the edge-emitting semiconductor laser diode. Therefore, modes 21 of an electromagnetic laser radiation generated within the active zone 15 in a resonator 17 of the semiconductor laser diode and impinging on the second partial surface 11 are attenuated, while modes 21 of the electromagnetic laser radiation impinging on the first partial surface 10 of the facet 12 are amplified.

[0122] Furthermore, the semiconductor laser diode according to the exemplary embodiment in FIGS. 14 and 15 has a ridge waveguide 9. The second partial surfaces 11 also partially cover the ridge waveguide 9 at the facet 12. The first partial surface 10 is arranged completely in the region of the ridge waveguide 9.

[0123] In contrast to the semiconductor laser diode according to the exemplary embodiment of FIGS. 16 and 17, the semiconductor laser diode according to the exemplary embodiment of FIGS. 14 and 15 has a facet 12 which has three first partial surfaces 10 and two second partial surfaces 11, the second partial surfaces 11 being arranged between the first partial surfaces 10. The first partial surfaces 10 have a lower roughness and thus a higher reflectivity for electromagnetic laser radiation generated in a resonator 17 than the second partial surfaces 11.

[0124] The two second partial surfaces 11 are in the present case strip-shaped and extend along a stacking direction R.sub.S of the epitaxial semiconductor layer stack 14. Furthermore, the two second partial surfaces 11 lie completely below a ridge waveguide 9.

[0125] The semiconductor laser diode according to the exemplary embodiment of FIGS. 18 and 19 has several partial surfaces 10, 11, 11, 11, 11, which have different vertical angles .sub.W1, .sub.W2, .sub.W3, .sub.W4 with a vertical main surface 6 of an epitaxial semiconductor layer stack 14. Furthermore, the different partial surfaces 10, 11, 11, 11, 11 have different roughnesses depending on the vertical angle .sub.W1, .sub.W2, .sub.W3, .sub.W4.

[0126] In contrast to the semiconductor laser diodes described so far, the semiconductor laser diode according to the exemplary embodiment of FIGS. 20 and 21 has a first partial surface 10 and two second partial surfaces 11, the second partial surfaces 11 each forming a second lateral angle .sub.L2 with a vertical main surface 6 of the epitaxial semiconductor layer stack 14. In contrast, the first partial surface 10 extends parallel to the vertical main surface 6. In addition, the first partial surface 10 is arranged between the second partial surfaces 11. Furthermore, the first partial surface 10 is smoothed with respect to the two second partial surfaces 11, so that the first partial surface 10 has a lower roughness than the two second partial surfaces 11.

[0127] In the semiconductor laser diode according to the exemplary embodiment of FIGS. 22 and 23, the second partial surfaces 11 are smoothed by a wet chemical method compared to the exemplary embodiment of FIGS. 20 and 21.

[0128] The semiconductor laser diode according to the exemplary embodiment of FIGS. 24 and 25 has a first partial surface 10 and a second partial surface 11, wherein the first partial surface 10 forms a first lateral angle du with a vertical main surface 6 and the second partial surface 11 forms a second lateral angle as. The first partial surface 10 and the second partial surface 11 are arranged directly adjacent to each other in a radiation exit region 13 of the facet 12 and form a cut-out 22 in the facet 12. The cut-out 22 has a triangular cross-sectional area in plan view of the semiconductor laser diode.

[0129] The semiconductor laser diode according to the exemplary embodiment of FIGS. 26 and 27, in contrast to the semiconductor laser diode according to the exemplary embodiment of FIGS. 24 and 25, has two cut-outs 22 in a radiation exit region 13 of the facet 12.

[0130] In contrast to the semiconductor laser diode of FIGS. 24 and 25, the semiconductor laser diode according to the exemplary embodiment of FIGS. 28 and 29 has a protrusion 23 on the facet 12 in the radiation exit region 13. The protrusion 23 is formed by a first partial surface and a second partial surface 11 on the facet 12, the first partial surface forming a first lateral angle and the second partial surface forming a second lateral angle with a vertical main surface.

[0131] In contrast to the semiconductor laser diode according to the exemplary embodiment of FIGS. 30 and 31, the semiconductor laser diode according to the exemplary embodiment of FIGS. 28 and 29 has a protrusion 23 which has a semicircular cross-sectional area in plan view.

[0132] In contrast to the semiconductor laser diode according to the exemplary embodiment of FIGS. 30 and 31, the semiconductor laser diode according to the exemplary embodiment of FIG. 32 has two protrusions 23 arranged next to each other, each of which has a semicircular cross-sectional area in plan view. The two protrusions 23 are arranged in a radiation exit region 13 of the facet 12.

[0133] FIG. 33 shows an exemplary scanning electron microscope image of an outer surface of a round protrusion 23, as shown schematically in FIGS. 31 and 32, for example. The depicted epitaxial semiconductor layer stack 14 is based on a nitride compound semiconductor material. In particular, the epitaxial semiconductor layer stack 14 is formed of gallium nitride.

[0134] Rounded protrusions 23 or cut-outs 22 in a facet 12 of the epitaxial semiconductor layer stack 14 can be generated by circular structuring (concave or convex) during plasma etching. In particular, a smooth and vertical first partial surface 10 is generated at an apex of the circular arc during a subsequent wet chemical etching when the circular arc coincides with the m-face of the gallium nitride crystal. In addition, a very rough second partial surface 12 is generated at the facet.

[0135] In contrast to the semiconductor laser diode according to the exemplary embodiment of FIGS. 34 and 35, the semiconductor laser diode according to the exemplary embodiment of FIGS. 30 and 31 has a facet 12 with a cut-out 22, which has a semicircular base area in plan view. Second partial surfaces 11, which have a comparatively high roughness, are arranged at the side of the cut-out 22.

[0136] The semiconductor laser diode according to the exemplary embodiment of FIG. 36 has a facet 12 with three cut-outs 22, each of which has a semicircular base area when viewed from above. The cut-outs 22 are arranged next to each other in a radiation exit region 13.

[0137] The array according to the exemplary embodiment of FIGS. 37 and 38 comprises several edge-emitting semiconductor laser diodes, as already described. In particular, each semiconductor laser diode has two cut-outs 22 with a base area that is triangular in plan view in a radiation exit region 13, which are arranged next to each other.

[0138] The invention is not limited to the description based on the embodiments. Rather, the invention includes any new feature as well as any combination of features, which includes in particular any combination of features in the patent claims, even if this feature or combination itself is not explicitly stated in the patent claims or embodiments.