SEMICONDUCTOR LASER AND PROJECTOR

Abstract

In an embodiment, the semiconductor laser (1) comprises a semiconductor layer sequence (2) in which an active zone (22) for generating laser radiation (L) is located. Several electrical contact surfaces (5) serve for external electrical contacting of the semiconductor layer sequence (2). Several parallel ridge waveguides (3) are formed from the semiconductor layer sequence (2) and configured to guide the laser radiation (L) along a resonator axis, so that there is a separating trench (6) between adjacent ridge waveguides. At least one electrical feed (4) serves from at least one of the electrical contact surfaces (5) to guide the current to at least one of the ridge waveguides (3). A distance (A4) between the ridge waveguides is at most 50 m. The ridge waveguides (3) are electrically controllable individually or in groups independently of one another and/or configured for single-mode operation.

Claims

1. A semiconductor laser comprising a semiconductor layer sequence in which an active zone for generating a laser radiation is located, at least two electrical contact surfaces for external electrical contacting of the semiconductor layer sequence, a plurality of parallel ridge waveguides, each of which is formed from the semiconductor layer sequence and each of which is configured to guide the laser radiation along a resonator axis so that at least one separation trench is present between adjacent ridge waveguides, and at least one electrical feed from at least one of the electrical contact surfaces to at least one of the ridge waveguides, where a distance between at least two adjacent ridge waveguides is at most 50 m, and the ridge waveguides are electrically controllable individually or in groups independently of one another and/or are configured for single-mode operation.

2. The semiconductor laser according to claim 1, further comprising a carrier on which the semiconductor layer sequence is attached by means of at least one organic or metallic connection means, wherein the semiconductor layer sequence is designed as a semiconductor chip and at least two of the contact surfaces are located on the carrier.

3. The semiconductor laser according to claim 2, in which the carrier comprises a plurality of electrical conductor tracks which electrically connect the contact surfaces on the carrier to the feeds via the connecting means, wherein at least one contact surface is provided on the carrier for each of the ridge waveguides.

4. The semiconductor laser according to claim 1, in which there is a flow stop layer between the contact surfaces of the carrier, wherein the flow stop layer is configured to prevent direct electrical connections between adjacent contact surfaces of the carrier.

5. The semiconductor laser according to claim 2, in which the connecting means is a solder or a continuously applied anisotropic electrically conductive adhesive.

6. The semiconductor laser according to claim 2, in which the semiconductor layer sequence partially covers at least one of the contact surfaces located on the carrier, wherein a further contact surface for all ridge waveguides in common is located on a side of the semiconductor layer sequence or of a growth substrate of the semiconductor layer sequence remote from the ridge waveguides.

7. The semiconductor laser according to claim 1, in which all contact surfaces are located on that side of the semiconductor layer sequence on which the ridge waveguides are formed, wherein an electrical connection line extends through the semiconductor layer sequence or over an edge of the semiconductor layer sequence, and wherein the contact surfaces are configured as soldering surfaces and/or as wire bonding surfaces.

8. The semiconductor laser according to claim 1, which is a flip chip.

9. The semiconductor laser according to claim 1, in which at least one of the contact surfaces is arranged asymmetrically to the associated ridge waveguide when viewed in top view, whereby, seen in top view, an arrangement of all contact surfaces together shows at most one axis of mirror symmetry.

10. The semiconductor laser according to claim 1, in which at least some of the ridge waveguides have different temperatures from one another during the intended operation of the semiconductor laser, so that, due to the different temperatures, a wavelength of maximum intensity of the laser radiation generated in the ridge waveguides varies by at least 1.5 nm and a temperature difference across the ridge waveguides is at least 30 K.

11. The semiconductor laser according to claim 1, in which at least some of the separating trenches are differently shaped from one another in cross-section, wherein the separation trenches are partially or completely filled with a passivation layer and/or with a heat conducting material.

12. The semiconductor laser according to claim 11, in which the passivation layer exhibits a thickness gradient so that in regions with a greater thickness of the passivation layer the associated ridge waveguides are thermally more strongly insulated.

13. The semiconductor laser according to claim 11, in which the heat conducting material only partially fills the separation trenches, wherein the heat conducting material is electrically insulating and contacts the semiconductor layer sequence, and wherein the heat conducting material is unevenly distributed across the separation trenches.

14. The semiconductor laser according to claim 11, in which the heat conducting material is electrically conductive and is applied to the passivation layer, wherein said heat conducting material contacts at least one of said feeds.

15. The semiconductor laser according to claim 1, in which at least some of the separating trenches are T-shaped when viewed in cross-section, and a width of the separating trenches decreases monotonically or strictly monotonically in the direction away from upper sides of the ridge waveguides, so that these separating trenches each have at least one step.

16. The semiconductor laser according to claim 1, comprising at least eight and at most 64 of the ridge waveguides, wherein the semiconductor layer sequence is based on the material system AlInGaN and the laser radiation has a wavelength of maximum intensity between 385 nm and 540 nm inclusive.

17. A projector having at least one semiconductor laser (1) according to claim 1 and having a lens for projecting the laser radiation generated during operation, wherein the lens is arranged jointly downstream of all ridge waveguides of the semiconductor laser concerned.

18. A semiconductor laser comprising a semiconductor layer sequence in which an active zone for generating a laser radiation is located, several electrical contact surfaces for external electrical contacting of the semiconductor layer sequence, a plurality of parallel ridge waveguides, each of which is formed from the semiconductor layer sequence and each of which is configured to guide the laser radiation along a resonator axis so that at least one separation trench is present between adjacent ridge waveguides, and several electrical feeds from at least one of the electrical contact surfaces to at least one of the ridge waveguides, and a carrier, to which the semiconductor layer sequence is applied by means of at least one connecting means, where a distance between at least two adjacent ridge waveguides is at most 50 m, and the ridge waveguides are electrically controllable individually or in groups independently of one another and/or are configured for single-mode operation, the carrier comprises several electrical conductor tracks that electrically connect the contact surfaces at the carrier via the connecting means to the feeds, and the semiconductor layer sequence is configured as semiconductor chip and all contact surfaces are located at the carrier, so that the semiconductor laser is surface-mountable.

Description

[0051] In the Figures:

[0052] FIGS. 1A, 2A and 3 show schematic top views of exemplary embodiments of semiconductor lasers described here,

[0053] FIGS. 1B, 2B and 2C show schematic sectional views of exemplary embodiments of semiconductor lasers described here,

[0054] FIGS. 1C and 4A show schematic perspective views of exemplary embodiments of semiconductor lasers described here,

[0055] FIGS. 4B and 5 show schematic top views of exemplary embodiments of semiconductor lasers described here,

[0056] FIGS. 6A and 6B show schematic sectional views of exemplary embodiments of semiconductor lasers described here,

[0057] FIGS. 7 to 10 show schematic sectional views of exemplary embodiments of semiconductor lasers described here, and

[0058] FIG. 11 shows a schematic sectional view of an exemplary embodiment of a projector described here with a semiconductor laser described here.

[0059] FIG. 1 illustrates an exemplary embodiment of a semiconductor laser 1. The semiconductor laser 1 has a semiconductor layer sequence 2. In the semiconductor layer sequence 2 there is an active zone 22 for generating laser radiation L. Optionally, the semiconductor layer sequence 2 is located on a growth substrate 26.

[0060] From the semiconductor layer sequence 2, several ridge waveguides 3 are formed by etching, for instance, wherein the ridge waveguides 3 are arranged parallel to one another. Seen in top view, the ridge waveguides 3 can all be designed the same within the manufacturing tolerances. Preferably, the ridge waveguides 3 do not reach the active zone 22. The ridge waveguides 3 can be so narrow that the semiconductor laser 1 is operated in single mode.

[0061] There are separation trenches 6 between adjacent ridge waveguides 3. Seen in cross section, the separation trenches 6 are T-shaped. An upper part of the separation trenches 6 is connected to the ridge waveguides 3 in a lateral direction, parallel to the active zone 22. A lower part of the separation trenches 6 can reach through the active zone 22.

[0062] Furthermore, electrical feeds 4 are located directly at the ridge waveguides 3, and the ridge waveguides 3 are supplied with current via the feeds 4. On a side of the growth substrate 26 facing away from the ridge waveguides 3 there can be a common electrical contact surface 5 for all ridge waveguides 3. The electrical feeds 4 are each uniquely assigned to the ridge waveguides 3.

[0063] It is possible that the electrical feeds 4 do not reach facets 30 of the semiconductor layer sequence 2. This prevents optical damage, COD for short or Catastrophic Optical Damage, to the facets 30, since no current is applied directly to the facets 30 or only a reduced current is applied to the active zone 22.

[0064] The semiconductor layer sequence 2 is preferably mechanically self-supporting together with the growth substrate 26 and can be handled with tweezers. Thus the semiconductor layer sequence 2 forms a semiconductor chip 20 with the growth substrate 26, the electrical feeds 4 and the electrical contact surface 5 on the growth substrate 26.

[0065] Furthermore, the semiconductor laser 1 comprises a carrier 7. The semiconductor chip 20 is mounted on electrical conductor tracks 74 of the carrier 7. There is a one-to-one assignment between the conductor tracks 74 and the electrical feeds 4. The feeds 4 and the assigned conductor tracks 74 can run congruently within the manufacturing tolerances, especially along a transverse direction y. It is possible that the feeds 4, seen in cross-section, especially in the yz plane, surround the associated ridge waveguides 3 in a U-shape. A thickness of the feeds 4 on side faces of the ridge waveguides 3 can be greater than on upper sides 35 of the ridge waveguides 3.

[0066] The ridge waveguides 3 are arranged close together. Thus a distance A4 between adjacent ridge waveguides 3 is preferably at least 2 m or 10 m and/or at most 50 m, in particular between 20 m and 40 m inclusive. A width A1 of the ridge waveguides 3 in the y-direction is preferably between 1.0 m and 2.5 m inclusive, in particular between 1.5 m and 2.1 m inclusive. A minimum width A2 of the separation trenches 6 in the active region of zone 22 is in particular between 2 m and 50 m, preferably between 2 m and 15 m. A mesa width A3 at one edge of the semiconductor chip 20 is preferably between 20 m and 80 m inclusive, in particular between 25 m and 55 m inclusive. A width A5 of the feeds 4 at the ridge waveguides 3 is preferably between 3 m and 20 m, in particular between 4 m and 8 m. Unless otherwise indicated, these values also apply to all other exemplary embodiments.

[0067] The contact surfaces 5 on the carrier 7 are configured as bonding surfaces. This means that the carrier 7 and thus the semiconductor laser 1 can be electrically contacted by means of bonding wires 8. An underside of the carrier 7 is preferably accessible by adhesive bonding or soldering. The carrier 7 can be configured as a heat sink and/or for heat dissipation and thus for cooling the semiconductor chip 20.

[0068] FIG. 2 illustrates another exemplary embodiment. Here, the external feeds 4 are designed asymmetrically with respect to the associated ridge waveguide 3. A width A6 of the outer feeds 4 is preferably between 10 m and 80 m, especially between 6 m and 20 m. The ridge waveguide 3 lies within the inner 10% to 45% of the width A6 with respect to the width A6, in particular within the inner 10% to 35% of the width A6.

[0069] FIGS. 2B and 2C further illustrate ways of mounting the semiconductor chip 2 on the carrier 7. The semiconductor chips 20 are mounted upside down on the carrier 7. Upside down means that the upper sides 35 of the ridge waveguides 3 each face the carrier 7.

[0070] As shown in FIG. 2B, a solder is used as the connecting means 72. On the carrier 7 there is preferably a flow stop layer 76 between the electrical contact surfaces 5 and/or the electrical tracks 74, for example made of a solder resist. This allows the connecting means 72 to be congruent with the tracks 74 and the feeds 4.

[0071] On the other hand, according to FIG. 2C, a continuous connecting means layer 72 is used, preferably made of an anisotropic conductive adhesive. Due to the anisotropic conductivity, electrical short circuits between adjacent tracks 74 are avoided. In addition, FIG. 2C illustrates that the contact surfaces 5 can be led through the carrier to the underside of the carrier 7 via vias 78, so that the semiconductor laser 1 can be surface-mounted as a whole. The vias 78 are drawn as dashed lines in FIG. 2C.

[0072] The electrical and mechanical connection between the semiconductor chips 20 and the carriers 7 described in FIGS. 2B and 2C can be present in all other exemplary embodiments accordingly. In contrast to the illustration, it is possible that the feeds 4 and the carriers 74 have different dimensions in the y-direction, for example to achieve mounting tolerances.

[0073] FIGS. 1B, 2B and 2C each show that the feeds 4 have a flat upper side facing away from the semiconductor layer sequence 2. This can be achieved, for example, by planarizing the feeds 4 or by anisotropically depositing a material for the feeds 4. Deviating from this it is possible in a preferred design that the feeds 4 have a constant thickness. Since the ridge waveguides 3 have only a small expansion in the z-direction, for example at least 0.2 m or 0.5 m and/or at most 10 m or 2 m, the difference in height then existing between the different areas of the electrical feeds 4 can be compensated for by varying the thickness of the connecting means 72. The same applies to all other exemplary embodiments.

[0074] In the exemplary embodiment shown in FIG. 3 there are only two ridge waveguides 3. FIG. 3, right half, shows a sectional enlargement from FIG. 3, left half.

[0075] The feeds 4 can also serve as contact surfaces 5 and are arranged asymmetrically to the respective ridge waveguides 3. In order to achieve a better connection of bonding wires at the contact surfaces 5, for example, these have a comparatively large width A7 close to the facets 30, which is preferably between 10 m and 200 m inclusive, and especially between 90 m and 120 m inclusive. Starting from these wide areas, narrower areas with a width A8 are given, which preferably serve as feeds 4 and not as contact surfaces. The width A8 is in particular between 10 m and 60 m, preferably between 45 m and 55 m. The asymmetry of the ridge waveguides 3 to the contact surfaces 5 is preferably pronounced in the same way as in FIG. 2. In the area with the reduced width A8 there may optionally be a marking 9, for example as a numbering or lettering.

[0076] An overall width A6 of the semiconductor chip 20 and/or the semiconductor laser 1 along the y-direction transverse to the ridge waveguides 3 is preferably at least 0.1 mm and/or at most 0.5 mm, in particular between 300 m and 450 m inclusive.

[0077] The explanations in FIG. 3 regarding the asymmetrical contact surfaces and feeds 4, 5 and the widths A6, A7, A8 apply accordingly to all other exemplary embodiments.

[0078] FIG. 4A illustrates a schematic diagram of how the semiconductor chip 20 is attached to the carrier 7. There are four symmetrically arranged contact surfaces 5 on the carrier 7 and a common contact surface 5 on the semiconductor chip 20.

[0079] FIG. 4B illustrates that two of the contact surfaces 5 on the carrier 7 are partially covered by the semiconductor chip 20.

[0080] FIG. 5 illustrates another design of carrier 7 and its contact surfaces 5, which can be used alternatively in conjunction with FIGS. 1 and 2. The contact surfaces 5 are each connected to one of the electrical contact surfaces 74 and have increasing widths in the y-direction away from the contact surfaces 74. In this way a comparatively symmetrical arrangement of the contact surfaces 5 on the carrier 7 can be achieved. The contact surfaces 5 can be free from the semiconductor chip 20.

[0081] FIG. 6 illustrates that all contact surfaces 5 are drawn to the side of the semiconductor layer sequence 2 with the ridge waveguides 3. In this case it is possible that no separate carrier or submount is required. In such a design of the semiconductor chip 20, a surface-mountable carrier with the vias 78 is preferred, as explained in connection with FIG. 2C.

[0082] As shown in FIG. 6A, an electrical connection line 27 is routed over side surfaces of the semiconductor layer sequence 2 and the optional growth substrate 26, so that the feed 4 is attached to a back side. Departing therefrom, as shown in FIG. 6B, the electrical connection line 27 is a via through the semiconductor layer sequence 2 and the optional growth substrate 26.

[0083] To simplify the illustration, electrical insulation layers and passivation layers for the electrical separation of the electrical contact surfaces 5 and the feeds 4, 4 as well as the connection lines 27 are not specifically shown in FIG. 6.

[0084] In the exemplary embodiments of FIGS. 7 to 10, the ridge waveguides 3 are thermally insulated and thermally coupled in different ways. This makes it possible to generate 3 laser beams L1, L2, L3 with different wavelengths of maximum intensity due to the different temperatures at the ridge waveguides during operation.

[0085] According to FIG. 7, a passivation layer 62, for example of silicon dioxide, has a thickness gradient. For example, the passivation layer 62 is thinner in a central area of the semiconductor chip 20, seen in the y-direction, and becomes increasingly thicker towards one edge. In the same way, it is possible that the feeds 4, seen in the y-direction, become thicker towards the center and thinner towards an edge, at least on the side faces of the ridge waveguides 3.

[0086] FIG. 8 illustrates that the separation trenches 6 are partially T-shaped. The separation trenches 6 are each partially filled by a material of the passivation layers 62a, 62b. There is a first passivation layer 62a and a second passivation layer 62b, which differ in their thermal conductivities. In particular, silicon carbide, aluminum nitride or diamond-like carbon, DLC for short, is used as the second passivation layer 62b with a high thermal conductivity. As first passivation layer 62a with a lower thermal conductivity, for example silicon nitride, silicon dioxide or aluminum oxide is used.

[0087] In the exemplary embodiment shown in FIG. 9, the separation trenches 6 have different designs. Closer neighboring ridge waveguides 3 are thermally more strongly coupled to each other via a heat conducting material 64. Such ridge waveguides 3 can also be electrically combined into groups, but are preferably electrically controllable independently of each other. The heat conducting material 64 is for example aluminum nitride, silicon carbide or diamond-like carbon. If the heat-conducting material 64 is an electrically conductive material, the respective feeds 4 can be electrically connected to each other via the heat-conducting material 64.

[0088] FIG. 10 illustrates that, unlike in FIG. 9, the heat conducting material 64 is not in direct contact with the semiconductor layer sequence 2, but is applied to the passivation layer 62. The heat conducting material 64 is, for example, a metal such as gold, platinum, nickel, palladium, titanium or silver.

[0089] In contrast to the illustrations in FIGS. 9 and 10, the heat-conducting material 64 can also completely fill the associated separation trenches 6. By means of the passivation layers 62, 62a, 62b and the heat-conducting material 64 drawn in FIGS. 7 to 10, it is possible to achieve not only an electrical connection or insulation of adjacent ridge waveguides 3 but also optical insulation of the ridge waveguides 3 from each other.

[0090] FIG. 11 illustrates an exemplary embodiment of a projector 10 for example for glasses for virtual reality applications. In particular, a lens 11 is attached to the carrier 7. The lens 11 is used to optically image the laser radiation L of all ridge waveguides 3 of the associated semiconductor chip 20. This allows a simplified and efficient imaging of the laser radiation 11.

[0091] Unless otherwise indicated, the components shown in the figures preferably follow one another in the order given. Layers not touching each other in the figures are preferably spaced apart. If lines are drawn parallel to each other, the corresponding surfaces are preferably aligned parallel to each other. Likewise, unless otherwise indicated, the relative positions of the drawn components to each other are correctly shown in the figures.

[0092] The invention described here is not limited by the description using the exemplary embodiments. Rather, the invention comprises each new feature as well as each combination of features, which in particular includes each combination of features in the claims, even if this feature or combination itself is not explicitly stated in the claims or exemplary embodiments.

[0093] This patent application claims the priority of the German patent application 10 2018 106 685.6, the disclosure content of which is hereby incorporated by reference.

LIST OF REFERENCE SIGNS

[0094] 1 semiconductor laser [0095] 2 semiconductor layer sequence [0096] 20 semiconductor chip [0097] 22 active zone [0098] 26 growth substrate [0099] 27 electrical connection line [0100] 3 ridge waveguide [0101] 30 facet [0102] 35 upper side of the ridge waveguide [0103] 4 electrical feed [0104] 5 electrical contact surface [0105] 6 separation trench [0106] 62 passivation layer [0107] 64 heat conducting material [0108] 7 carrier [0109] 72 connection means [0110] 74 electrical conductor track [0111] 76 flow stop layer [0112] 78 via [0113] 8 bonding wire [0114] 9 marking [0115] 10 projector [0116] 11 lens [0117] A distance/width [0118] L laser radiation