SEMICONDUCTOR LASER AND PRODUCTION METHOD FOR A SEMICONDUCTOR LASER

Abstract

In one embodiment, the invention relates to a semiconductor laser comprising a semiconductor layer sequence for generating laser radiation. According to the invention, the semiconductor layer sequence has a geometric structuring on a top side. A resonator is located in the semiconductor layer sequence and is delimited by opposing facets, wherein the facets contain optically active resonator end faces. The structuring ends spaced apart from the facets. The resonator end faces are spaced apart from material removals from the semiconductor layer sequence.

Claims

1. A semiconductor laser with a semiconductor layer sequence for generating laser radiation, wherein the semiconductor layer sequence comprises at least one geometric structuring on a top side a resonator in the semiconductor layer sequence is bounded by two opposing facets of the semiconductor layer sequence, so that the facets comprise optically effective resonator end faces, the structuring ends at a distance from at least one of the facets, and at least one of the resonator end faces is spaced apart from material removals from the semiconductor layer sequence.

2. The semiconductor laser according to claim 1, wherein the facets are smooth planar surfaces produced by means of breaking, wherein the facets are rectangular in a plan view on the facets.

3. The semiconductor laser according to claim 1, in which the structuring comprises a ridge waveguide which comprises a broadening towards each of the facets, so that the semiconductor laser is a refractive index guided laser, wherein the broadenings at the facets extend over an entire width of the semiconductor layer sequence at the top side.

4. The semiconductor laser according to claim 3, in which the broadenings are trapezoidal and/or funnel-shaped as seen in a plan view of the top side.

5. The semiconductor laser according to claim 3, in which each broadening is limited to a region directly at the facets, and the ridge waveguide outside the broadening comprises a constant, uniform width, wherein a length of each broadening is at most 10% of a length of the resonator.

6. The semiconductor laser according to claim 1, wherein the semiconductor laser is a gain-guided laser without refractive index guidance.

7. The semiconductor laser according to claim 6, in which the patterning comprises at least two trenches for reflecting away parasitic laser modes, wherein the trenches extend along the resonator.

8. The semiconductor laser according to claim 1, wherein the structuring comprises at least one H-shaped protrusion as seen in a plan view of the top side, wherein a center bar of said H extends along the resonator.

9. The semiconductor laser according to the preceding claim 8, wherein the H is asymmetrically shaped as seen in a plan view, such that the center bar and the resonator are eccentrically located in the top side.

10. The semiconductor laser according to claim 1, in which the structuring comprises a frame which bounds the semiconductor layer sequence on the top side all around, wherein a maximum thickness of the semiconductor layer sequence is present at the frame.

11. The semiconductor laser according to claim 1, wherein an acoustic layer is provided on at least one of the facets on the top side of the semiconductor layer sequence, wherein the acoustic layer has a lower sound velocity than the semiconductor layer sequence, wherein the acoustic layer is arranged at a distance from electrical contact pads of the semiconductor laser and is limited to a strip at the associated facet.

12. The semiconductor tor laser according to claim 1, in which, at the facets and as seen in a plan view of the facets, a distance of the optically effective resonator end faces, which are configured for reflection and/or for coupling out the laser radiation generated in operation, towards a material removal out of the semiconductor layer sequence is at least 40 μm and/or at least one fivefold of a mean diameter of the resonator end faces.

13. The semiconductor laser according to claim 1, wherein an initiator region is generated at at least one of the facets and spaced apart from the associated resonator end face, which initiator region is configured as an initial region for breaking the semiconductor layer sequence, wherein the said facet comprises a greater roughness at the initiator region than at the associated resonator end face.

14. The semiconductor laser according to claim 1, which comprises a plurality of resonators, so that the semiconductor laser is a laser bar with a plurality of laser units.

15. The semiconductor laser according to claim 1, further comprising a carrier with a carrier structure, wherein the semiconductor layer sequence is attached to the carrier at the top side, wherein the carrier structure corresponds to the structuring of the semiconductor layer sequence, so that the carrier and the semiconductor layer sequence can be adjusted to each other with a lateral tolerance of at most 5 μm.

16. A production method for semiconductor lasers according to claim 1 comprising the steps: growing the semiconductor layer sequence, structuring the semiconductor layer sequence by material removal, so that the at least one geometric structuring is formed, and generating the facets by breaking, wherein the breaking takes place only in those regions of the semiconductor layer sequence from which no material of the semiconductor layer sequence was previously removed.

17. The method according to claim 16, by which a semiconductor laser comprising an initiator region is produced, wherein the initiator regions are generated by means of laser irradiation, such that the top side and a bottom side of a growth substrate for the semiconductor layer sequence are planar at the facets.

18. A semiconductor laser with a semiconductor layer sequence for generating laser radiation, wherein the semiconductor layer sequence comprises at least one geometric structuring on a top side a resonator in the semiconductor layer sequence is bounded by two opposing facets of the semiconductor layer sequence, so that the facets comprise optically effective resonator end faces, the at least on geometric structuring ends at a distance from at least one of the facets, at least one of the resonator end faces is spaced apart from material removals from the semiconductor layer sequence, and an acoustic layer is provided on at least one of the facets on the top side of the semiconductor layer sequence, wherein the acoustic layer has a lower sound velocity than the semiconductor layer sequence.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In the Figures:

[0065] FIGS. 1 to 3 show in each case figure parts A a plan view and in figure parts B a side view of exemplary embodiments of semiconductor lasers described herein,

[0066] FIG. 1C shows a schematic side view of the semiconductor laser of FIGS. 1A and 1B,

[0067] FIGS. 4 and 5 show schematic side views of exemplary embodiments of semiconductor lasers described herein,

[0068] FIG. 6 shows in figure part A a schematic plan view and in the figure part B a schematic sectional view of a method step for production of semiconductor lasers described herein,

[0069] FIGS. 7 and 8 show schematic plan views of exemplary embodiments of semiconductor lasers described herein,

[0070] FIG. 9A shows a schematic plan view and FIG. 9B a schematic side view of an exemplary embodiment of a semiconductor laser described herein,

[0071] FIG. 10 shows a schematic plan view of an exemplary embodiment of a semiconductor laser described herein,

[0072] FIGS. 11, 12A and 12B show schematic side views of exemplary embodiments of semiconductor lasers described herein, and

[0073] FIG. 13 a schematic plan view of an exemplary embodiment of a semiconductor laser described herein.

DETAILED DESCRIPTION

[0074] FIG. 1 shows an exemplary embodiment of a semiconductor laser 1. The semiconductor laser 1 comprises a semiconductor layer sequence 2 with an active zone 22 for generating a laser radiation L. Preferably, the semiconductor layer sequence 2 is based on the material system AlInGaN. The semiconductor layer sequence 2 may still be located on a growth substrate 27. For example, the growth substrate 27 is a GaN substrate.

[0075] A structuring 5 is formed on a top side 20 of the semiconductor layer sequence 2. The structuring 5 includes a ridge waveguide 50. A resonator 4 is defined by the ridge waveguide 50. Via the ridge waveguide 50, an index guidance of the laser radiation L within the semiconductor layer sequence 2 is performed.

[0076] The resonator 4 is bounded in the longitudinal direction by two facets 3 of the semiconductor layer sequence 2. The facets 3 are each planar over the entire surface and are generated by means of breaking. In a plan view on the facets 3, the facets 3 are rectangular.

[0077] Each facet 3 includes a resonator end face 42. The resonator end faces 42 are those regions of the facets 3 at which the laser radiation L is reflected at the facets 3 and/or emerges from the facets 3. Thus, the resonator end faces 42 are located in a region of the resonator 4 and the active zone 22 as seen in a plan view of the facets 3, see FIG. 1C. Remaining regions of the facets 3 are optically essentially inactive. Seen in a plan view, the resonator end faces 42 are elliptical or circular, for example.

[0078] In order that the facets 3 may be generated over the entire surface in high quality, the ridge waveguide 50 comprises broadenings 51 towards the facets 3 and the resonator end faces 42. The broadenings 51 are rectangular in shape when viewed from above and extend along the top side 20 along the entire facets 3, see FIG. 1A. The ridge waveguide 50 together with the broadenings 51 form an H-shaped protrusion 54, which forms the structuring 5.

[0079] Thus, there are no regions at the facets 3 where a material removal of the semiconductor layer sequence 2 has been carried out after a growth. In particular, etchings for the ridge waveguide 50 do not extend to the facet 3.

[0080] It is possible that the active zone 22 is located below the ridge waveguide 50. That is, the active zone 22 is preferably not affected by the structuring 5.

[0081] Optionally, an electrical contact pad 71 is located extending above the ridge waveguide 50, see in particular FIG. 1B. The electrical contact pad 71 is preferably formed by one or more metallizations. Seen from above, the contact pad 71 can be rectangular in shape. It is possible that the electrical contact pad 71 comprises bulges towards the facets 3 in a region of the ridge waveguide 50. The broadenings 51 are free of the contact pad 71. The contact pad 71 preferably extends on both sides of the ridge waveguide 50 onto the top side 20.

[0082] Optionally, a further electrical contact pad 73 is located on a bottom side 28 of the growth substrate 27 facing away from the semiconductor layer sequence 2. Thus, the semiconductor laser 1 is electrically contactable from two opposite main sides.

[0083] Seen in a plan view and in the direction perpendicular to the resonator 4, the broadenings 51 preferably extend to at least 200 μm or 100 μm or 50 μm away from the ridge waveguide 50. Thus, side surfaces 25 of the semiconductor laser 1 which extend transversely to the facets 3 are comparatively far away from the ridge waveguide 50. An extension T of the broadenings 51 along the resonator 4 is preferably at least 1 μm or 3 μm. Alternatively or additionally, this extension T of the broadenings 51 is at most 100 μm or 30 μm. Alternatively or additionally, this extension T of the broadenings 51 along the resonator 4 is preferably at most 10% or 5% of a total length R of the resonator 4 in each case. The corresponding applies preferably also in all exemplary embodiments.

[0084] In FIG. 1C it is further illustrated that a distance D between the lying ellipse-shaped resonator end face 42 and a material removal or a material processing at the facets 3 and seen in a plan view of the facets 3 is relatively large and preferably at least 100 μm. Thus, material defects in a region of material removal or material processing do not exert a significant influence on the semiconductor material of the resonator end face 42.

[0085] Since there is preferably no material removal or material processing on the top side 20, the distance D in this case is measured towards the side surface 25, which is produced, for example, by means of breaking, etching or sawing. Furthermore, it can be seen in FIG. 1C that this distance towards regions of the top side 20 in regions adjacent to the ridge waveguide 50 would be almost zero without the broadening 51, see the dash lines in FIG. 1C illustrating the ridge waveguide 50.

[0086] In FIG. 2, it is shown that an acoustic layer 61 is applied along each of the facets 3 on the top side 20 on the broadenings 51. The acoustic layer is used to guide a breaking wave when the facets are broken. The acoustic layer 61 is preferably made of a speed of sound adapted material. For example, the acoustic layer 61 is made of silicon dioxide, Si.sub.3N.sub.4, SiON, ZnO, ITO or Al.sub.2O.sub.3 or combinations of insulating layers. Furthermore, it is possible that the acoustic layer 61 is of a semiconductor material such as silicon, of an II-VI semiconductor material, or of a III-N semiconductor material. Preferably, the acoustic layer 61 is made of at least one metal such as titanium, palladium, nickel, platinum and/or gold.

[0087] A thickness of the acoustic layer 61 is preferably at least 10 nm or 50 nm. Alternatively or additionally, the thickness of the acoustic layer 61 is at most 2 μm or 1 μm. It is possible that in the direction away from the top side 20 the contact pad 71 rises above the acoustic layer 61, as shown in FIG. 2B. Alternatively, the contact pad 71 and the acoustic layer 61 may be flush with each other in the direction away from the top side 20, or the acoustic layer 61 may rise above the contact pad 71.

[0088] In all other respects, the statements with respect to FIG. 1 can apply mutatis mutandis to FIG. 2.

[0089] In the exemplary embodiment of FIG. 3, the semiconductor laser 1 additionally comprises an initiator region 62 on each of the facets 3. Starting from the initiator regions 62, the facets 3 are generated by means of breaking. The initiator regions 62 are located, for example, on the surface 20 at ends of the facets 3.

[0090] Preferably, the initiator regions 62 are generated via laser radiation by means of stealth dicing, laser scribing or via a diamond scribe. A depth of the initiator regions 62 is preferably at least 100 nm and/or at most 90% of a thickness of the semiconductor layer sequence 2 or a thickness of the semiconductor layer sequence 2 together with the growth substrate 27, not drawn in FIG. 3. An extension of the initiator regions 62 in the direction parallel to the facets 3 is preferably at least 2 μm or 10 μm or 30 μm and/or at most 200 μm or 100 μm.

[0091] Such initiator regions 62 may be provided in a wafer composite during fabrication of the semiconductor lasers 1 for each semiconductor laser 1 or may occur only in one semiconductor laser per a certain number of semiconductor lasers, for example, only in every second or every fifth semiconductor laser.

[0092] A width of the trenches in the direction parallel to the resonator 4 is preferably relatively small and is for example at least 0.2 μm or 0.5 μm and/or at most 20 μm or 10 μm.

[0093] In FIG. 4 it is illustrated that the initiator regions 62 are not located at the top side 20, but at the bottom side 28. In contrast, it is shown in FIG. 5 that the initiator regions 27 are located within the compound of the semiconductor layer sequence 2 and the growth substrate 27. This is made possible in particular by the fact that the initiator regions 62 are created by stealth dicing. The explanations regarding the dimensions of the initiator regions 62, as explained with respect to FIG. 3, apply accordingly to FIGS. 4 and 5.

[0094] Such initiator regions 62, as illustrated in connection with FIGS. 3 to 5, may also be present in all other exemplary embodiments.

[0095] In FIG. 6A, a wafer composite 10 is illustrated in which several of the semiconductor lasers 1 are still directly adjacent to each other. Along breaking lines 81 the facets 3 are generated. Along singulation lines 82 the semiconductor lasers 1 can be singulated in a direction parallel to the resonators 4. Singulation along singulation lines 82 is, for example, also a breaking, but can also be performed by other methods such as sawing or laser irradiation.

[0096] Along line A-A of FIG. 6A, a sectional view is shown in FIG. 6B. It is illustrated that initiator regions 62 are created along the singulation lines 82 using stealth dicing.

[0097] The semiconductor lasers 1, as illustrated in FIG. 6B, comprise the ridge waveguide 50. Further, trenches 52 are provided through which parasitic laser modes and/or stray light can be reflected or absorbed away. In addition, see FIG. 6A, a circumferential frame 53 is provided, which bounds the semiconductor lasers 1 at the top side 20 all around. Thus, the breaking lines 81 and the singulation lines 82 extend exclusively through regions of the semiconductor layer sequence 2 from which no material has been removed.

[0098] As in all other exemplary embodiments, it is possible for the contact pad 71 to extend over a large area of the semiconductor layer sequence 2. In order to allow only localized current supply of the semiconductor layer sequence 2, a passivation layer 63 is then preferably applied. The passivation layer 63 is, for example, made of an oxide such as silicon oxide and may comprise a thickness, for example, of at least 20 nm and/or of at most 800 nm.

[0099] Such additional trenches 52 and a frame 53, as illustrated in FIG. 6, may also be present in all exemplary embodiments.

[0100] In the exemplary embodiment of the semiconductor laser 1 shown in FIG. 7, a width of the broadening 51 first increases linearly in the direction toward the facet 3 before a sudden increase in the width occurs. The broadening 51 thus comprises a trapezoidal region and a rectangular region, as seen in a plan view of the top side 20. Viewed along the resonator 4, an extension of the trapezoidal region is, for example, at least twice and/or at most ten times the extension of the rectangular region.

[0101] By such a geometry of the broadening 51, in particular monomode lasers with a high optical output power can be obtained. Preferably, such broadenings 51 are present on both facets 3, as shown in the left half of FIG. 7. Corresponding broadenings 51 may also be present in all other exemplary embodiments.

[0102] A thickness of the broadening 51 in the direction perpendicular to the top side 20 is preferably equal to a thickness of the ridge waveguide 50, but may also comprise a value different therefrom. For example, the ridge waveguide 50 and/or the broadening 51 comprise a thickness of at least 0.2 μm or 0.5 μm or 1 μm and/or of at most 5 μm or 3 μm in a direction away from the active zone 22. A total thickness of the semiconductor layer sequence 2 as grown on growth substrate 27 is for example at least 4 μm and/or at most 12 μm.

[0103] Deviating from FIG. 7, it is illustrated in FIG. 8 that the broadening 51 merges steadily and without kinks into the actual ridge waveguide 50. In all other respects, the statements with respect to FIG. 7 also apply to FIG. 8.

[0104] In FIG. 9, in an exemplary embodiment it is shown, that the semiconductor laser 1 is a gain-guided laser. Again, there are no etchings or other material removals extending to the facets 3. Initiator regions 62 may be present on the side surfaces 25 oriented perpendicular to the facets 3, which do not extend to the facets 3 and which may be located in the semiconductor layer sequence 2, together with the growth substrate 27. To avoid parasitic modes, the semiconductor laser 1 of FIG. 9 preferably comprises slopes on the side surfaces 25, not shown, which can form a patterning.

[0105] In FIG. 10, it is illustrated that the gain-guided laser comprises trenches 52 on either side of the resonator 4 within the top side 20. Thus, the circumferential frame 53 is present. The trenches 52 are, for example, V-shaped or trapezoidal in cross-section when viewed perpendicular to the top side 20 and perpendicular to the resonator 4. It is possible for the contact pad 71 to extend closer to the facets 3 than the trenches 52.

[0106] In FIG. 11 it is illustrated that the semiconductor laser 1 additionally comprises a carrier 70. The carrier 70 is, for example, a submount and may comprise electrical structures for contacting the semiconductor laser 1. The contact pad 71 is connected to the carrier 70 via a bonding means 74. The bonding means 74 is, for example, a solder. Thus, the top side 20 of the semiconductor layer sequence 2 faces the carrier 70.

[0107] Due to the broadening 51 extending along the facets 3, the risk of tilting of the semiconductor layer sequence 2 about an axis of rotation parallel to the resonator 4 is reduced. Thus, the semiconductor layer sequence 2 can be arranged parallel to an upper side of the carrier 70 with high precision.

[0108] FIGS. 12A and 12B illustrate a method of attaching the semiconductor layer sequence 2 to the carrier 70. The carrier 70 comprises carrier structures 72, for example in the form of trenches. Alternatively, the carrier structures 72 may be formed by elevations.

[0109] FIG. 12B illustrates that, for example, when the contact pad 71 is soldered to the carrier 70, a kind of self-alignment results due to the carrier structure 72. This means that small manufacturing tolerances can be achieved in a direction parallel to the resonator 4. For example, an accuracy with which the facets 3 are flush with side surfaces of the carrier 70 is in the range between 1 μm and 5 μm. If it is not desired for at least one of the facets 3 to be flush with the carrier 70, the carrier structures 72 can also be designed asymmetrically in order to set a specific, desired overhang of the facets 3 over the carrier 70.

[0110] In the exemplary embodiment of FIG. 13, the semiconductor laser 1 is a laser bar. Thus, the semiconductor laser 1 comprises several laser units 11. The laser units 11 may be electrically controllable independently of each other or may be electrically operable together. The broadening 51 preferably extends completely along the facets 3 of the laser bar.

[0111] The acoustic layers 61 shown in FIG. 2, the initiator regions 62 of FIGS. 3 to 6, and the broadenings 51 of FIGS. 7 and 8, and also the carriers 70 as shown in FIGS. 11 and 12, may each be present in combination with one another in the exemplary embodiments.

[0112] The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.