LASER DIODE WITH INTEGRATED THERMAL iris

Description

[0001] The present invention relates to a laser diode with an integrated thermal aperture. State of the art

[0002] Broad-area diode lasers (BALs) can exhibit exceptionally high efficiency and brilliance. These emitters can reliably achieve output powers exceeding 15 W. BALs are the most efficient light source for near-infrared (NIR) radiation, making them widely used as pump sources for solid-state and fiber lasers. They are also a key element of fiber-coupled laser systems designed to deliver high-radiation-density beams for material processing with high wand-to-plug efficiencies. To increase the output power of these systems and reduce their cost, improving the slow-axis beam quality is crucial, as this enables the coupling of a greater number of emitters in low numerical aperture (NA) fibers.

[0003] At high optical output powers and the associated operating currents, however, a significant deterioration of beam quality generally occurs, which has a particularly negative impact on coupling in fibers. It has been shown that thermal lensing (and not charge carrier or gain-induced guiding) in the slow axis is one of the predominant causes of beam quality deterioration at increased operating currents (Bai, JG et al., Mitigation of Thermal Lensing Effect as a Brightness Limitation of High-Power Broad Area Diode Lasers, Proc. SPIE 7953, 79531F (2011)).The decisive factor for the deterioration of beam quality at high output powers is therefore the formation of a lateral temperature gradient due to a temperature increase in the central area under the laser stripe, which leads to a local increase in the refractive index and thus to additional lateral wave propagation and consequently to a larger divergence angle.

[0004] To improve heat transfer, lengthening the laser resonator or influencing the thermal flux between the laser diode and the submount (thermal path technology; see, e.g., Bai et al., DE 10 2013 114 226 B4 and US 2016 0315 446 A1) have been proposed. This reduces the lateral temperature gradient and thus flattens the generated thermal lens. However, diode lasers with longer resonators have higher manufacturing costs. Recently, it was shown that a high thermal barrier forms at the interface between the laser diode and a corresponding metallization, which significantly reduces the effectiveness of thermal path technology on the thermal lens (Rieprich, J. et al., Chip-carrier thermal barrier and its impact on lateral thermal lens profile and beam parameter product in high power broad area lasers, J. Appl. Phys. 123, 125703 (2018)).

[0005] Another way to reduce the lateral temperature gradient is to additionally heat the laser diode with an external heat source (Hohimer, JP, Mode control in broad area diode lasers by thermally induced lateral index tailoring, Appl. Phys. Lett. 52, 260 (1988)). However, integrating an external heat source into a diode laser is very complex and therefore not very practical.

[0006] A reduction in the lateral temperature gradient can also be achieved through a specially adapted layer structure (Winterfeldt, M. et al., Assessing the Influence of the Vertical Epitaxial Layer Design on the Lateral Beam Quality of High-Power Broad Area Diode Lasers, Proc. SPIE 9733, 97330O (2016)). However, such adaptations only marginally improve the lateral beam quality. Furthermore, such adaptations are only possible with certain laser designs.

[0007] US 2001 / 0017870 A1 relates to a multi-mode, high-power semiconductor laser with a wide active or light-emitting region. M. Elattar et al., Semicond. Sci. Technol. 35 (2020) 095011 describes a laser diode with a wide active region based on the GaAs material system and a thin InGaP constriction layer.

[0008] US 8,233,513 B1 discloses an edge-emitting wide-strip diode laser with reduced thermal contact to minimize the divergence of the laser beam in the slow axis. Disclosure of the invention

[0009] It is therefore an object of the present invention to provide a laser diode in which the lateral temperature gradient can be reduced and the generated thermal lens flattened. In particular, the laser diode should not require an external heat source or modifications to the chip-external layer structure (e.g., metallization), i.e., it should be based solely on monolithically integrated structures within the diode laser.

[0010] These problems are solved according to the invention by the features of claim 1. Advantageous embodiments of the invention are contained in the respective dependent claims.

[0011] A laser diode according to the invention comprises an active layer formed between an n-doped semiconductor material and a p-doped semiconductor material, wherein the active layer forms an active zone with a width w along a longitudinal axis for generating electromagnetic radiation; wherein a layer-shaped thermal aperture with a thermal conductivity coefficient is formed in the p-doped semiconductor material k block smaller than a thermal conductivity coefficient k bulk of the p-doped semiconductor material (for example, in the p-doped semiconductor material between the active zone and a cooled underside of the laser diode) is formed for spatially selective heat transport from the active zone to a side of the p-doped semiconductor material opposite the active layer; or in the n-doped semiconductor material, a layer-shaped thermal aperture with a thermal conductivity coefficient kblock smaller than a thermal conductivity coefficient k bulk of the n-doped semiconductor material is configured for spatially selective heat transport from the active zone to a side of the n-doped semiconductor material opposite the active layer, wherein the laser diode is based on GaAs or Al x Ga 1-x As and the thermal aperture is made of InGaP, InGaAsP, InGaAsSb or an InGaP-InGaAsP superlattice, and wherein the thermal aperture has an aperture thickness d block has a thickness between 0.3 µm and 3 µm.

[0012] A thermal aperture according to the invention can thus be formed in both p-doped and n-doped semiconductor materials, preferably being formed within the respective semiconductor material. In the following, a p-sided thermal aperture is used as an example; however, the descriptions apply analogously to an n-sided thermal aperture.

[0013] A laser diode is understood to be a layered structure consisting of a semiconductor material, with or without metallization (so-called laser chip). The term semiconductor material is used here generically to refer to any semiconductor material or a combination of semiconductor materials, for example, a combination from the AllnGaAsNSb material system. In particular, n-doped semiconductor material and p-doped semiconductor material can each comprise layered systems of corresponding different types or doped semiconductor materials in various compositions. The usage is therefore to be understood as synonymous with the terms n-sided semiconductor material and p-sided semiconductor material.

[0014] An active layer is formed at the interface between the n-doped and p-doped semiconductor materials. The generation of electromagnetic radiation takes place in the electrically pumped region of the active layer within the active zone. A large portion of the heat generated during the operation of the laser diode is produced there and must be dissipated. This can be achieved, in particular, via a submount, which, for example, can be thermally connected to the underside of the laser diode below the active zone. The connection between the underside of the laser diode and the submount is state of the art and can be made, in particular, by soldering or bonding.

[0015] According to the invention, a layer-shaped thermal aperture with a thermal conductivity coefficient is formed in the p-doped semiconductor material. k block smaller than a thermal conductivity coefficient kThe bulk of the surrounding p-doped semiconductor material below the active zone is designed for spatially selective heat transfer from the active zone to the underside of the laser diode. The thermal conductivity (also known as thermal conductivity or thermal conductivity coefficient) determines the heat flow through a material due to thermal conduction. The lower this value, the worse the thermal conductivity of the material. According to the invention, a thermal aperture is intended to reduce the lateral temperature gradients (i.e., flatten the thermal lens) by locally increasing the thermal resistance in the conventional expansion area (laterally below the active zone) in the lateral direction, thus counteracting a spatial lateral expansion of the heat flow in the region between the active zone and the underside of the laser diode.Due to their increased thermal resistance, the local temperature of the side regions (of the thermal aperture) rises when more heat is generated within the strip (in the central region) with increasing output power. This corresponds to a lower temperature gradient between the central region and the side regions, and thus a flatter thermal lens.

[0016] Regarding the relationship between the two thermal conductivity coefficients, the thermal conductivity coefficient is particularly important. k The thermal conductivity of the p-doped semiconductor material is concentrated in the bulk below the active zone. In a multi-layered p-doped semiconductor material, the individual layers can each have slightly different thermal conductivity coefficients. k exhibit layer. The thermal conductivity coefficient kbulk can then be considered the resulting thermal conductivity of all layers involved in the heat flow. The thermal conductivity can be approximated as follows: k For the bulk of the p-doped semiconductor material below the active zone, an average thermal conductivity coefficient of the p-doped semiconductor material can also be assumed. Alternatively, the thermal conductivity coefficient can be used as an approximation. k bulk of the p-doped semiconductor material also with the thermal conductivity coefficient k KS can be equated with a p-contact layer of the p-doped semiconductor material.

[0017] The idea of ​​the present invention lies particularly in the fact that a flat thermal lens can be realized by integrating a monolithically integrated thermal aperture (internal thermal path technology) directly into the laser diode. External thermal path technologies are less effective in comparison due to the presence of the intrinsic semiconductor-metal thermal barrier. Furthermore, a thermal aperture according to the invention can be positioned very close to the active zone, thus minimizing the expansion of the heat flow in the lateral direction, resulting in a particularly flat thermal lens. The thermal path technology known from the prior art can therefore be applied within the laser diode, thereby significantly increasing its effectiveness and efficiency.

[0018] The thermal aperture is made of a semiconductor material. This material should have a particularly low thermal conductivity (for low thermal conductivity coefficients). kblock). Furthermore, high electrical conductivity is preferred. The thermal conductivity coefficient k The thermal conductivity can be reduced by changing the indium and / or phosphorus content (e.g., GaAs and AlGaAs as p-type semiconductor materials, InGaP or InGaAsP as a thermal orifice). Preferably, the thermal orifice is designed to achieve particularly low thermal conductivity coefficients. k a block is formed from periodically alternating materials (for example, different semiconductors or semiconductors and air), with a high number of regular changes between the materials, with many interfaces exhibiting large differences in thermal conductivity. k Layers are formed. Heat transfer across interfaces is limited and leads to a further reduction in thermal conductivity. kblock (see J. Piprek et al., Thermal conductivity reduction in GaAs-AlAs distributed Bragg reflectors, in IEEE Photon. Tech. Lett. 10, 81(1998)). Preferably, the thermal aperture can be realized with a photonic crystal structure. A photonic crystal structure is understood to be a 3D periodic nanostructure that can influence the movement of photons within the crystal lattice. Typically, to generate a high refractive index contrast, openings ("air holes") filled with air or other particularly low refractive index materials are formed in the structures. These openings and the numerous material transitions are responsible for a particularly high reduction in thermal conductivity in these materials. In summary, photonic crystal structures allow the creation of regions with good optical properties and very low thermal conductivity.The same applies to 1-D periodic lattices (superlattices), in which thin layers of two different materials, and in particular semiconductor materials, are arranged alternately on top of each other.

[0019] With a laser diode according to the invention, the optical properties of the area below the active zone can thus be largely preserved despite an additional thermal aperture.

[0020] For laser diodes based on GaAs ( k KS ≈ 44 W / (m K)) or Al x Ga 1-x As ( k KS ≈ 11-91 W / (m·K)) a thermal aperture made of InGaP ( k block ≈ 5 W / (m K)). InGaAsP ( k block ≈ 5 W / (m·K)), InGaAsSb or an InGaP-InGaAsP superlattice ( k block ≈ 2.5 W / (m·K)).

[0021] For sufficient glare reduction, the thermal conductivity coefficient should be k The block should be as small as possible. The thermal conductivity coefficient kThe block should preferably be a maximum of 30%, more preferably a maximum of 10%, more preferably a maximum of 5%, and most preferably a maximum of 1% of the corresponding bulk value. k bulk. A thermal conductivity coefficient can be determined using an InGaP-InGaAsP superlattice. k block reach, which is approximately half the value for the thermal conductivity coefficient k of InGaP and InGaAsP (see J. Piprek et al., Thermal conductivity reduction in GaAs-AlAs distributed Bragg reflectors, in IEEE Photon. Tech. Lett. 10, 81 (1998)). However, significantly lower thermal conductivities can also be achieved through photonic crystal structures.

[0022] Preferably, the thermal aperture forms a slit-shaped passage parallel to the active layer, allowing heat to flow from the active zone towards an outer surface (e.g., a p-side underside equipped with a heat sink in the case of a p-side thermal aperture) of the laser diode. In such an arrangement, the thermal aperture can restrict the heat flow along the entire resonator axis (z-axis) to a slit-shaped passage. A centrally symmetrical arrangement of the slit-shaped passage with respect to the active zone (medial arrangement) is preferred for efficiency reasons.

[0023] Preferably, the following applies to the lateral distance: dx between an outer edge of the active zone (lateral boundary in the lateral direction) and the nearest inner edge of the thermal aperture (lateral boundary facing the active zone in the lateral direction) -w / 6 ≤ dx ≤ +w / 6. This means that the distance preferably depends on the width w of the active zone and is selected such that the inner edge of the thermal aperture can have both a positive and a negative lateral distance to the outer edge of the active zone. A distance is particularly preferred dx of 0, i.e., when the outer edge of the active zone and the corresponding inner edge of the thermal aperture coincide spatially when projected onto the underside of the laser diode.

[0024] Preferably, the following applies to the vertical distance: dy between the center of the active layer and the top of the thermal aperture 0 µm ≤ dy≤ 1 µm. This means that the top surface of the thermal aperture is preferably located directly below the center of the active layer and at most 1 µm away from it. The smallest possible distance provides the highest aperture effect, but can negatively impact the optical properties. At a distance greater than 1 µm, the lateral expansion of the heat flow may no longer be effectively suppressed.

[0025] The thermal aperture has an aperture thickness. d The block thickness is between 0.3 µm and 3 µm. A thicker thermal orifice can result in greater suppression of the lateral expansion of the heat flow.

[0026] Preferably, the p-doped semiconductor material (with integrated thermal aperture) has a total layer thickness d between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm, and even more preferably between 2 µm and 3 µm.

[0027] Preferably, a layered thermal aperture is formed in the n-doped semiconductor material and a layered thermal aperture is formed in the p-doped semiconductor material. The thermal aperture in the n-doped semiconductor material can be functionally equivalent to the thermal aperture in the p-doped semiconductor material. Therefore, all specifications given in this description regarding the thermal aperture in the p-doped semiconductor material apply accordingly, taking into account the change in doping. Preferably, the thermal aperture in the n-doped semiconductor material and the thermal aperture in the p-doped semiconductor material can be symmetrical with respect to the active layer. This symmetry can relate in particular to the geometric and / or material configuration of the thermal apertures.The design of the thermal apertures can also differ, for example, if the p-doped and n-doped semiconductor materials have different thicknesses and an adjustment of the spacing is necessary. Such an embodiment is advantageous if the laser diode is mounted for double-sided cooling, i.e., if heat extraction can occur on both sides of the laser diode.

[0028] Further preferred embodiments of the invention result from the features mentioned in the dependent claims.

[0029] Unless otherwise specified in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another as long as the resulting combinations of features still fall within the scope of the claimed subject matter. Brief description of the drawings

[0030] The invention is explained below using exemplary embodiments with reference to the accompanying drawing. The drawing shows: Fig. 1 a schematic representation of an exemplary conventional laser diode without a thermal aperture, Fig. 2 a schematic representation of an exemplary first embodiment of a laser diode according to the invention with a thermal aperture, Fig. 3 a simulation of the temperature as a function of the lateral position (x-axis) within the active zone, Fig. 4 a simulation of the normalized thermal lens curvature factor |B2| as a function of the thermal conductivity coefficient k KS of the p-contact layer, Fig. 5 a simulation of the normalized thermal lens curvature factor |B2| as a function of the aperture thickness d block , Fig. 6 a simulation of the normalized thermal lens curvature factor |B2| as a function of the lateral distance dx, Fig. 7 a simulation of the temperature difference ΔT between the temperature T as a function of the lateral position (x-axis) and the peak temperature T peak at position x = 0 for structures with the KS material according to Fig. 4 , and Fig. 8 a schematic representation of an exemplary second embodiment of a laser diode according to the invention with two thermal apertures. Detailed description of the drawings

[0031] Figure 1 Figure 1 shows a schematic representation of an exemplary conventional laser diode without a thermal aperture. The diode laser shown comprises a laser diode 10 with an active layer 14 formed between an n-doped semiconductor material 12 and a p-doped semiconductor material 16, wherein the active layer 14 has an active zone 40 with a width along a longitudinal axis. wfor generating electromagnetic radiation; and a submount 30, wherein the submount 30 is thermally connected to the p-side underside of the laser diode 10 below the active zone 40. The thermally conductive connection can be formed by an intermediate solder layer 20, wherein the solder is intended to enable optimal heat transfer between the underside of the laser diode 10 and the submount 30.

[0032] The laser diode 10 can in particular have a multilayer structure with an n-substrate, an n-cladding layer on the n-substrate, an n-waveguide layer on the n-cladding layer, an active layer 14 on the n-waveguide layer, a p-waveguide layer on the active layer 14, a p-cladding layer on the p-waveguide layer, a p-contact layer on the p-cladding layer, and a metallic p-contact on the p-contact layer.

[0033] The heat losses occurring in the active zone 40 during operation of the laser diode must be dissipated from the active zone 40. A submount 30 is typically used as a heat sink (e.g., a heat sink) for this purpose. However, the heat flow from the active zone 40 to the submount 30 spreads significantly in a lateral direction, leading to an inhomogeneous temperature distribution in the area below the active zone 40. This temperature distribution can then exert thermo-optical effects on the generated electromagnetic radiation and, through the formation of a thermal lens in this area, contribute to a deterioration of the beam quality during radiation emission.

[0034] Figure 2Figure 1 shows a schematic representation of an exemplary first embodiment of a laser diode with a thermal aperture according to the invention. The diode laser shown comprises a laser diode 10 with an active layer 14 formed between an n-doped semiconductor material 12 and a p-doped semiconductor material 16, wherein the active layer 14 has an active zone 40 with a width along a longitudinal axis (longitudinal direction, z-axis). w for the generation of electromagnetic radiation; and a submount 30, wherein the submount 30 is thermally connected below the active zone 40 to the p-side underside of the laser diode 10. This corresponds insofar as to FIG. 1 described structure.

[0035] However, in the p-doped semiconductor material 16, there is also a layered thermal aperture 18 with a thermal conductivity coefficient k block smaller than a thermal conductivity coefficient kThe bulk of the p-doped semiconductor material 16 (below the active zone 40) is designed for spatially selective heat transport from the active zone 40 to the side of the p-doped semiconductor material 16 opposite the active layer 14 (underside of the laser diode 10) and thus to the submount 30. The thermal conductivity coefficient can be approximated as follows: k For the bulk of the p-doped semiconductor material below the active zone 40, an average thermal conductivity coefficient of the p-doped semiconductor material 16 can also be assumed. Alternatively, the thermal conductivity coefficient can be approximated. k bulk of the p-doped semiconductor material 16 also with the thermal conductivity coefficient k KS can be equated to a p-contact layer of the p-doped semiconductor material 16.

[0036] The thermally conductive connection can also be formed by an intermediate solder layer 20, whereby the solder should enable optimal heat transfer between the underside of the laser diode 10 and the submount 30. The connection can also be made by adhesive bonding, e.g., using a thermally conductive adhesive.

[0037] The thermal aperture 18 forms a slit-shaped passage parallel to the active layer 14 for a heat flow 42 directed from the active zone 40 towards the underside of the laser diode 10. In the figure, the slit-shaped passage is arranged medially below the active zone 40. Lateral propagation of the heat flow 42 directed from the active zone 40 to the submount 30 is suppressed by the thermal aperture 18 according to the invention, resulting in a largely parallel heat flow 42. The high thermal resistance of the thermal aperture 18 leads to an increase in its local temperature (i.e., heating in the side regions) when more heat is generated by the active zone 40 with increasing output power.This results in a more uniform temperature distribution in the area below active zone 40 between the central area (directly below the active zone) and the thermal aperture (the side areas). The formation of a thermal lens in this area is thus also suppressed, which can improve the beam quality during radiation emission.

[0038] The diagram still shows the horizontal distance. dx between an outer edge of active zone 40 and the nearest inner edge of the thermal aperture. The vertical distance is also shown. dy between the center of the active layer 14 and the thermal aperture 18. The aperture thickness is also shown in the diagram. d block of the thermal aperture 18 and the total layer thickness d of the p-doped semiconductor material 16.

[0039] The description also applies accordingly to a thermal aperture 18 formed in the n-doped semiconductor material 12. In this case, to suppress a lateral widening of an upwardly directed heat flow 42, a corresponding submount 30 above the active zone 40 could be thermally connected to the n-side top of the laser diode 10.

[0040] Figure 3Figure 1 shows a simulation of the temperature as a function of the lateral position (x-axis) within the active zone. The simulation was performed at a vertical position (y-axis) of y = 0, i.e., in the center of the active layer, for a GaAs-based broad-area diode laser (BAL) with a stripe width w = 90 µm (see M. Elattar et al., High-brightness broad-area diode lasers with enhanced self-aligned lateral structure, Semicond. Sci. Technol. 35, 095011 (2020)), operating at an optical power Popt = 10 W. The simulated BAL corresponds to the typical setup consisting of an active zone (AZ) between an n-doped and a p-doped semiconductor material. The p-doped semiconductor material consists of an Al x Ga 1-x As waveguide layer (WL) grown on the AZ, followed by an Al x Ga 1-x As cladding layer (MS) and finally a GaAs contact layer (KS) on which a contact metal is subsequently deposited.The simulation (aligned with corresponding experimental results) includes a thermal barrier at the chip-metal interface. The thermal lens curvature factor B2 is defined as the quadratic term of a quadratic fit of the resulting thermal profile (Rieprich, J. et al., Chip-carrier thermal barrier and its impact on lateral thermal lens profile and beam parameter product in high power broad area lasers, J. Appl. Phys. 123, 125703 (2018)), where a quadratic fit was applied in the simulation for the area within the strip width w = 90 µm. The exemplary conventional diode laser in the simulation shows that a thermal profile with a curved gradient develops, ranging from approximately 45 °C at the edges to approximately 51 °C in the center of the broad strip.

[0041] Figure 4 shows a simulation of the normalized thermal lens curvature factor |B2| as a function of the thermal conductivity coefficient. kKS of the p-contact layer. In the reference structure, the KS consists of GaAs ( k KS ≈ 44 W / (m·K)). If GaAs is replaced by materials with lower thermal conductivity, such as InGaP ( k block ≈ 5 W / (m K)), InGaAsP ( k block ≈ 5 W / (m·K)), an InGaP-InGaAsP superlattice ( k block ≈ 2.5 W / (m K); see J. Piprek et al., Thermal conductivity reduction in GaAs-AlAs distributed Bragg reflectors, in IEEE Photon. Tech. Lett. 10, 81(1998)), or air ( k When the thermal conductivity of air is replaced with a coefficient of ≈ 0.026 W / (m·K), the normalized thermal lens curvature factor |B2| is reduced, which corresponds to a weakened thermal lens. This leads to a smaller far-field angle and thus to improved beam quality. In particular, the simulation showed that a 5% reduction in the normalized thermal lens curvature factor |B2| through a reduced thermal conductivity coefficient kA thermal conductivity of approximately 18 W / (m·K) can be achieved. A reduction of 10% can be achieved with a thermal conductivity coefficient of 10%. k KS ≈ 7 W / (m·K) can be achieved. For a reduction of 15%, the thermal conductivity coefficient should be k KS ≈ 2.5 W / (m·K).

[0042] Figure 5 shows a simulation of the normalized thermal lens curvature factor |B2| as a function of the aperture thickness. d When layers of GaAs (KS) or Al x Ga 1-x As (MS, WL) are replaced by InGaP (low thermal conductivity k), the normalized thermal lens curvature factor |B2| is reduced, corresponding to the formation of a weakened thermal lens. This results in a smaller far-field angle and thus improved beam quality. In particular, the simulation showed that a 5% reduction in the normalized thermal lens curvature factor |B2| with an aperture thickness of dA block of approximately 688 nm can be achieved. A reduction of 10% can be achieved with a smaller aperture thickness. d block ≈ 1375 nm can be reached.

[0043] Figure 6 shows a simulation of the normalized thermal lens curvature factor |B2| as a function of the lateral distance. dx The KS was assumed to consist of InGaP. It can be observed that thermal diaphragms can most effectively reduce the thermal lens curvature factor |B2| when dx = 0, i.e., the thermally highly conductive slit-shaped passage area below the active zone is perfectly aligned medially with the laser stripe.

[0044] Figure 7 shows a simulation of the temperature difference Δ T between the temperature T as a function of the lateral position (x-axis) and the peak temperature T peak at position x = 0 for structures with the KS material according to Fig. 4The curve shows the reduction in the curvature of the thermal lens when GaAs is replaced by materials with lower thermal conductivity.

[0045] Figure 8 Figure 1 shows a schematic representation of an exemplary second embodiment of a laser diode according to the invention with two thermal apertures. The laser diode 10 shown corresponds in principle to a laser diode described in Figure 10. Fig. 2 The first embodiment of a laser diode 10 according to the invention with a thermal aperture 18 is shown. The individual reference numerals and their respective assignment to the individual features apply accordingly. In contrast to the illustration in Fig. 2However, the embodiment shown here incorporates thermal baffles 18 according to the invention both in the p-doped semiconductor material 16 below the active layer 14 and in the n-doped semiconductor material 12 above the active layer 14. A first submount 30a is thermally connected below the active zone 40 to a bottom surface of the laser diode 10. Furthermore, a second submount 30b is thermally connected above the active zone 40 to a top surface of the laser diode 10. Cooling can thus occur on both sides of the laser diode 10, whereby a lateral expansion of the heat flow 42 to both the top and bottom surfaces of the laser diode 10 can be effectively suppressed by the thermal baffles 18. Such an embodiment is advantageous when the laser diode 10 is mounted for double-sided cooling, i.e., when heat extraction can occur on both sides of the laser diode 10.The laser diode shown is symmetrical with respect to the active layer 14. Reference symbol list

[0046] 10 Laser diode 12 n-doped semiconductor material 14 Active layer 16 p-doped semiconductor material 18 Thermal aperture 20 Solder layer 30 Submount 30 First submount 30 Second submount 40 Active zone 42 Heat flow dx lateral distance (slow axis) dy vertical distance (fast axis) d block aperture thickness wwidth

Claims

1. A laser diode (10), comprising: an active layer (14) formed between an n-doped semiconductor material (12) and a p-doped semiconductor material (16), wherein the active layer (14) forms an active zone (40) with a width w along a longitudinal axis for generating electromagnetic radiation; wherein in the n- or p-doped semiconductor material (12, 16), a layered thermal aperture (18) with a thermal conductivity coefficient kblock smaller than a thermal conductivity coefficient kbulk of the correspondingly doped semiconductor material (12, 16) is formed for spatially selective heat transport from the active zone (40) to a side of the correspondingly doped semiconductor material (12, 16) opposite to the active layer (14); wherein the laser diode (10) is based on GaAs or AlxGa1-xAs, and the thermal aperture is made of InGaP, InGaAsP, InGaAsSb, or an InGaP-InGaAsP superlattice; and the thermal aperture (18) has an aperture thickness dblock between 0.3 µm and 3 µm.

2. The laser diode (10) according to claim 1, wherein the thermal aperture (18) is formed from periodically alternating materials.

3. The laser diode (10) according to any one of the preceding claims, wherein the thermal aperture (18) is formed as a photonic crystal structure.

4. The laser diode (10) according to any one of the preceding claims, wherein the thermal aperture (18) is electrically conductive.

5. The laser diode (10) according to any one of the preceding claims, wherein the thermal aperture (18) forms a slit-shaped passage region arranged parallel to the active layer (14) for a heat flow (42) directed from the active zone (40) towards an outer side of the laser diode (10).

6. The laser diode (10) according to claim 5, wherein the slit-shaped passage region is arranged medially with respect to the active zone (40).

7. The laser diode (10) according to any one of the preceding claims, wherein the n- or p-doped semiconductor material with the thermal aperture (18) has a total layer thickness d between 0.5 µm and 10 µm.

8. The laser diode (10) according to any one of the preceding claims, wherein a lateral distance dx between an outer edge of the active zone (40) and a nearest inner edge of the thermal aperture (18) is -w / 6 ≤ dx ≤ +w / 6.

9. The laser diode (10) according to any one of the preceding claims, wherein a vertical distance dy between a center of the active layer (14) and a top of the thermal aperture (18) is 0 µm ≤ dy ≤ 1 µm.

10. The laser diode (10) according to any one of the preceding claims, wherein the thermal conductivity coefficient kblock is at most 30% of the corresponding thermal conductivity coefficient kbulk.

11. The laser diode (10) according to any one of the preceding claims, wherein the layered thermal aperture (18) is formed both in the n-doped semiconductor material (12) and in the p-doped semiconductor material (16).