Broad-area semiconductor laser with improved beam quality

Abstract

The invention relates to a semiconductor laser with improved beam quality, in particular a semiconductor-based high-performance laser bar with a reduced thermal lens and reduced lateral far-field divergence which is achieved by an inhomogeneous subcontact structure in a contact region. A contact region of a single broad-area laser emitter comprises a semiconductor contact layer (12) of an epitaxial layer of the broad-area laser emitter, a metallic contact layer (10) for making planar surface contact with the semiconductor contact layer (12), wherein in the semiconductor contact layer (12), a structured region (14) with individual subcontacts (16) is formed for spatially splitting, under the metal contact layer (10), an operating current which can be supplied over the metal contact layer (10), wherein the width (wsub) and / or spacing (asub) of the individual subcontacts (16) of the structured region (14) varies in a lateral direction of the broad-area laser emitter.

Description

[0001] title

[0002] Broad-area semiconductor lasers with improved beam quality

[0003] Description

[0004] The present invention relates to a semiconductor laser with improved beam quality and in particular to a semiconductor-based high-power laser bar with reduced thermal lensing and reduced lateral far-field divergence due to an inhomogeneously formed sub-contact structure in a contact region.

[0005] State of the art

[0006] High-power semiconductor lasers with low beam divergence are crucial in many applications. For example, kW-class semiconductor laser bars contain several broad-area lasers (BALs) arranged in parallel, which typically have a lateral stripe width 1 / 1 / between 50 pm and 1200 pm. Corresponding laser bars with a power of approximately 2 kW in quasi-continuous or 1 kW continuous operation have already been successfully implemented (MJ Miah et al., "Optimizing vertical and lateral waveguides of kW-class laser bars for higher peak power, efficiency and lateral beam quality," IEEE Photon. J. 14 (3), p. 1525505, 2022; P. Crump et al., "Increased conversion efficiency at 800 W continuous wave output from single 1-cm diode laser bars at 940 nm," CLEO / Europe-EQEC, 2021).

[0007] However, the heat-Ztemperature profile within the individual emitters as well as in the entire laser bar represents a major limit to achieving even higher power levels and for the beam quality (i.e., for the beam parameter product (BPP)). Experimental studies (M. Winterfeldt et al., “High beam quality in broad area lasers via suppression of lateral carrier accumulation,” IEEE Photon. Technol. Lett. 27 (17), p. 1809, 2015; P. Crump et al., “Experimental studies into the beam parameter product of GaAs high-power diode lasers,” IEEE J. Sci. Top. Quant. Electron 28 (1), p. 1501111 , 2021) show that a strong thermal lens forms during laser operation and that the resulting lens effect becomes increasingly pronounced at higher operating power.

[0008] For example, Figure 1 shows the simulated temperature distributions within a 1 cm wide GaAs laser bar of the kW class, which comprises 8 BAL emitters with a lateral stripe width l / l / ~ 1100 m at different power dissipations. To avoid the excitation of unwanted lateral modes, the individual emitters of the laser bar have homogeneously substructured GaAs contact layers. In the simulation shown as an example, these structures in the semiconductor contact layer had individual subcontacts, each with a width of 20 pm and a spacing of 9 pm (corresponding to a period of 29 pm). The middle 6 emitters (emitters 2 to 7) of the laser bar show symmetric and largely identical temperature distributions, while the outer edge emitters (emitters 1 and 8) show asymmetric temperature distributions with a significantly reduced temperature towards the edges of the emitter.At an operating power of 1 kW (corresponding to a power loss of approximately 603 W), the temperature deviation ΔT between the center of the middle emitters and their edges is 4.4 K. For the edge emitters (emitters 1 and 8), the deviation between the respective center and the edges even increases to over 10 K. The resulting thermal lens, which is generated in the simulated laser bar within each individual emitter, gives rise to more higher-order modes and consequently degrades the beam quality of the emitters.

[0009] Various approaches are known in the state of the art to mitigate the thermal lensing effect in the individual emitters and in the laser bar to improve the BPP. This can be achieved, for example, by adapting the epitaxial design (P. Crump et al., "Increased conversion efficiency at 800 W continuous wave output from single 1-cm diode laser bars at 940 nm," CLEO / Europe-EQEC, 2021) or by forming a structured metal contact (A. Bachmann et al., "Recent brightness improvement of 976 nm high-power laser bars," Proc. SPIE 10086, p. 1008602, 2017).

[0010] Further approaches to improving the BPP of high-power lasers or laser bars by flattening the temperature profile within the laser module are based, for example, on changing the design of the epitaxial layer (DE 10 2020 133 368 A1) and the lateral bar layout, the use of pedestals (J.G. Bai et al., Proc SPIE 7953, 79531 F-1 , 2011), or additional heat input (JP Hohimer et al., "Mode control in broad-area diode lasers by thermally induced lateral index tailoring," Appl. Phys. Lett. 52 (4), 260-262, 1988). Although the thermal lensing effect can already be significantly reduced with the measures known in the prior art, it must be further suppressed to provide even higher power levels and further improve beam quality. Disclosure of the Invention

[0011] It is therefore an object of the present invention to provide a semiconductor laser with reduced thermal lensing and reduced lateral far-field divergence, in which, in order to improve the BPP, the thermal lensing effect in the individual emitters or in the laser bar is reduced by varying the temperature profile in the lateral direction on the basis of an existing epitaxial structure, ie without complex adjustments in the basic epitaxial design or in the layer structure.

[0012] These objects are achieved according to the invention by the features of independent patent claims 1, 11, and 12. Expedient embodiments of the invention are contained in the respective subclaims. In particular, a homogeneous substructure distribution in the contact region of broad-area laser emitters in laser bars, already known in the prior art, is adapted for this purpose (MJ Miah et al., "Optimizing vertical and lateral waveguides of kW-class laser bars for higher peak power, efficiency, and lateral beam quality," IEEE Photon. J. 14 (3), p. 1525505, 2022) and fundamentally further developed to solve the stated problem.

[0013] A contact region of a broad-area laser emitter according to the invention comprises a semiconductor contact layer of an epitaxial layer of the broad-area laser emitter, a metallic contact layer for the surface contacting of the semiconductor contact layer, wherein in the semiconductor contact layer a structured region with individual sub-contacts is formed below the metallic contact layer for the spatial splitting of an operating current that can be supplied via the metallic contact layer, wherein the width w / sub and / or the distance a SU b of the individual subcontacts varies in a lateral direction of the broad-area laser emitter (ie, within a single laser diode along the slow axis). Furthermore, a broad-area laser emitter with a contact region according to the invention is provided.

[0014] Broad-area laser emitters are well known in the art; reference is made to the relevant technical literature. Such semiconductor laser structures feature an epitaxial layer of differently doped semiconductor materials, with radiation generation occurring at the boundary between an n-doped and a p-doped region through recombination of corresponding charge carriers. The charge carriers are typically introduced into the epitaxial structure via a metallic contact layer (along the vertical axis of the semiconductor laser). To adapt to the metallic contact layer, the epitaxial layer has a so-called semiconductor contact layer as an adaptation layer at the boundary. This layer enables the metal-semiconductor junction to be realized with the lowest possible contact resistance.

[0015] Furthermore, the formation of a substructure in the semiconductor contact layer below the metallic contact layer is known in the prior art (MJ Miah et al., “Optimizing vertical and lateral waveguides of kW-class laser bars for higher peak power, efficiency and lateral beam quality,” IEEE Photon. J. 14 (3), p. 1525505, 2022). This serves in particular to avoid the excitation of unwanted lateral modes in the broad-area laser emitter. In the prior art, however, the substructures are formed such that the width w SU b and the distance a SU b of the individual subcontacts in the semiconductor contact layer below the metallic contact layer is constant in a lateral direction. The substructure distribution is thus homogeneous. In contrast, the present invention realizes an inhomogeneous substructure distribution, so that the width w SU b and / or the distance a SUb of the individual subcontacts in the semiconductor contact layer below the metallic contact layer of the laser emitter varies in a lateral direction.

[0016] The structured region with the individual subcontacts can be limited to the semiconductor contact layer and extend partially or completely through it (in the tangential direction of the broad-area laser emitter). The structured region can also extend beyond it into one or more underlying epitaxial layers. The structuring creates alternating conductive regions with low electrical resistance (subcontacts) and regions with high electrical resistance (barrier regions between adjacent subcontacts in the structured region of a single broad-area semiconductor laser).

[0017] Increased heat is generated in those regions that are supplied with current via the individual subcontacts (i.e., by the individual current-carrying regions formed in the structured semiconductor contact layer). If the distribution of the regions pumped in a structured manner by the current flow within the laser stripe is changed, the resulting heat distribution in the emitter also changes, which can be utilized according to the invention for the positive effect of flattening the thermal lens. In the invention presented, the heat distribution is thus redistributed by changing the size and mutual arrangement of the individual subcontacts of a substructure already known per se with a homogeneous substructure distribution within the semiconductor contact layer.

[0018] For example, increasing the width of the individual subcontacts at the edges of the laser stripe allows for a higher total current due to the increasingly lower electrical resistance, which in turn leads to higher total local power dissipation of the subcontacts. Wider subcontacts therefore have a higher overall heat load and increase the proportion of heating toward the edges of the laser stripe. This, in turn, minimizes the temperature drop at the emitter edges and ultimately leads to an overall flatter temperature profile.

[0019] Additionally, if the mutual distance between the individual sub-contacts decreases, the pumped regions exhibit a stronger thermal interaction with each other, which prevents a significant temperature drop in the unpumped region between the pumped regions and thus also results in a flatter temperature distribution.

[0020] The idea of ​​the present invention is therefore based on the use of an inhomogeneously structured contact region to flatten the temperature profile within a single semiconductor laser emitter (also referred to as a laser stripe, laser diode, broad-area emitter, or similar) and thus to reduce lateral beam divergence. In contrast to homogeneous, periodically structured contact regions in the prior art, which extend across the entire width of each individual laser stripe in a conventional laser bar (see Figure 1), wider subcontacts are preferably used towards the edges of the emitters. This approach can be used to improve the power and beam quality of both single emitters with a large aperture and laser bars constructed from several such single emitters, if the substructure distribution is tailored accordingly to their thermal profiles.

[0021] Preferably, the contact area of ​​the broad-area laser emitter extends over a lateral stripe width W > 150 pm, more preferably W > 200 pm. This is the lateral stripe width W of an individual broad-area laser emitter. Preferably, the broad-area laser emitter has a length of L > 2 mm in the longitudinal direction. Preferably, the width of a sub-contact w SU b 200 pm, preferred w SU b < 50 pm.

[0022] Preferably, the distance between adjacent sub-contacts a SU b 50 pm, preferred a SU b < 20 pm, more preferably a SU b < 10 pm. Preferably, the distance between adjacent subcontacts of the substructure a SUb > 1 pm. Such minimum distances allow for simplified provision of the structures, for example, using photoresist. Small distances between adjacent subcontacts allow for a high fill factor F of the substructure. This avoids losses (e.g., due to increased electrical series resistance). The period of the subcontacts p sub is over w SU b and a SU b by p sub = w SU b + a SU b is defined. Preferably, p varies sub less than 20%, more preferably less than 10%, in a single broad-area laser emitter, even more preferably p sub for all subcontacts and distances a SU b equal.

[0023] Preferably, the fill factor F of the substructure is between 30% and 95%, more preferably between 60% and 95%. The fill factor F is defined as the ratio between the pumped area (i.e., the total width of all n subcontacts, nxivsub ) within the single emitter and the total width of the single emitter W (width of all sub-contacts and their distances), F = (nxw SU b) / W.

[0024] Preferably, the width of the sub-contacts w SU b in the semiconductor contact layer below the metallic contact layer towards the edges of the structured area and / or the distance of the sub-contacts a SU b in the semiconductor contact layer below the metallic contact layer towards the edges of the structured area, whereby the variation of the width w SU b and / or the distance a SUb is preferably at least 10% of the width from the center of the structured region to its edges. A variation in the width is understood to mean the relative difference between the width of the subcontacts in the center of the emitter and the width of the subcontacts at the edge of the emitter. Similarly, a variation in the spacing of the subcontacts is understood to mean the relative difference between the spacing of the subcontacts in the center of the emitter and the spacing of the subcontacts at the edge of the emitter.

[0025] Preferably, the width w varies SU b and / or the distance a SU b of the subcontacts in the semiconductor contact layer below the metallic contact layer additionally in a longitudinal direction from a front side of the broad-area laser emitter to a rear side of the broad-area laser emitter. Preferably, the width of the subcontacts w SU b in the longitudinal direction and / or the distance of the sub-contacts aSU b in the longitudinal direction, where the variation of the width w SU b and / or the distance a SUb from the front of the broad-area laser emitter to the back of the broad-area laser emitter is preferably at least 10%. Such a variation of the substructure along the resonator axis can be used primarily to compensate for temperature fluctuations in the longitudinal direction. In particular, to reduce the current flow and lower the local temperature, the individual subcontacts below the metallic contact layer on the front of the broad-area laser emitter can be at least 10% narrower than on the back of the broad-area laser emitter. The contact region according to the invention is preferably produced by structuring the resistance of the semiconductor contact layer by implanting or doping foreign atoms, or by implementing pn junctions, for example via two-step epitaxy or the incorporation of wide bandgap layers.This preferably results in a 100-fold increase in electrical resistance in the implanted or doped regions. The substructures can be formed using implantation and / or epitaxial overgrowth techniques with a typical residual layer thickness of 2 pm > d. res > 0 pm. The residual layer thickness is defined as the distance between one side of the active layer (e.g., its top side) and the side of the implanted / doped region facing the active layer (e.g., its bottom side). A metallic contact layer can preferably be a galvanic gold layer (Au) on at least one metal alloy layer stack (e.g., Ti / Pt / Au).

[0026] A further aspect of the present invention relates to a laser bar comprising a plurality of broad-area laser emitters arranged side by side, wherein at least one broad-area laser emitter is configured with a contact region according to the invention. Preferably, all broad-area laser emitters of the laser bar are configured with a contact region according to the invention. Depending on the specific design, between approximately 5 and 80 individual emitters can preferably be arranged in an exemplary laser bar with a typical bar width WLB = 1 cm.

[0027] Preferably, at least one broad-area laser emitter with a contact region according to the invention is arranged in the central region of the laser bar, and the individual sub-contacts of the broad-area laser emitter are formed symmetrically in the lateral direction with respect to the center of the structured region. Preferably, all broad-area laser emitters arranged in the central region of the laser bar have a contact region according to the invention, wherein the individual sub-contacts of these broad-area laser emitters are formed symmetrically in the lateral direction with respect to the center of the structured region.

[0028] Preferably, at least one broad-area laser emitter with a contact region according to the invention is arranged in the edge region of the laser bar, and the individual sub-contacts of the broad-area laser emitter are formed asymmetrically in the lateral direction with respect to the center of the structured region. Preferably, all broad-area laser emitters arranged in the edge region of the laser bar have a contact region according to the invention, wherein the individual sub-contacts of these broad-area laser emitters are formed asymmetrically in the lateral direction with respect to the center of the structured region.

[0029] Preferably, the variation of the width w SU b and / or the distance a SU b of the sub-contacts from the center of the structured region towards the central region of the laser bar is smaller than towards the edges of the laser bar, wherein the difference in variation is preferably at least 10%.

[0030] Since, for example, in the 1 cm diode laser bar with 8 emitters shown as an example in Figure 1, the middle emitters (emitters 2-7) have a symmetrical temperature profile, the sub-contacts of the individual broad-area laser emitters with a contact area according to the invention should preferably be arranged symmetrically on both sides (ie, to the left and right of the center of each of the corresponding emitters). Preferably, the width of the sub-contacts w SU b is symmetrical and monotonic towards both edges of the corresponding emitters. It is also preferred that the distance a SU b between the subcontacts is reduced symmetrically and monotonically towards both edges of the corresponding emitters.

[0031] The variation of the width w SU b and / or the distance a SUb of the subcontacts should preferably be at least 10% from the center to the edges of the corresponding emitters. Such inhomogeneous subcontacts with a symmetrical arrangement with respect to the center of the corresponding emitters can preferably be used in the central emitters of the laser bar, which typically account for at least 30% of the total emitters in the laser bar.

[0032] Since the edge emitters shown in Figure 1 (emitters 1 and 8) exhibit a strongly asymmetric temperature profile compared to the center emitters (stronger variation at the outer edges), the subcontacts on both sides should preferably also be arranged asymmetrically. Since the temperature drop is much greater on one side than on the other, the variation in the width w should also preferably be SU b and / or the distance a SU b of the sub-contacts on this side starting from the center of the emitter will be larger.

[0033] For an edge emitter, the variation of the width w SU b and / or the distance a SU b of the sub-contacts from the center to the outer edge of the emitter, where the temperature drop is higher, should preferably be at least 20%, while the variation of the width w SU b and / or the distance a SU b the subcontacts on the other side of the emitter, where the temperature drop is lower, should preferably be smaller. Such inhomogeneous subcontacts with an asymmetric arrangement with respect to the center of the corresponding emitters should preferably be used in the emitters near the edges of the laser bar, which typically account for at least one to approximately 35% of the total emitters on each side of the laser bar.

[0034] Further preferred embodiments of the invention result from the features mentioned in the subclaims.

[0035] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0036] Short description of the drawings

[0037] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show:

[0038] Fig. 1 simulated lateral temperature distributions in a conventional 1 cm diode laser bar of the kW class with 8 emitters (width W = 1100 pm) at different power dissipation on a heat sink with a thermal resistance R th = 0.05 K / W;

[0039] Fig. 2 (a) simulated lateral temperature distributions along a single emitter

[0040] (width l / l / = 1100 pm) in a 1 cm diode laser bar of the kW class with thermal resistance Rth = 0.05 K / W at 0.6 kW and 1.0 kW operating power and an emitter spacing of d = 255 pm (7 emitters, stronger thermal lens) and d = 65 pm (8 emitters, weaker thermal lens) as well as (b) the measured lateral far-field divergence angles of individual emitters in a 1 cm diode laser bar of the kW class with thermal resistance R th = 0.05 K / W and its dependence on the operating power up to 1 kW (d = 255 pm with a wider lateral far field and d = 65 pm with a narrower lateral far field);

[0041] Fig. 3 is a schematic representation of the formation of substructures with conventional homogeneous and inventive inhomogeneous substructure distribution;

[0042] Fig. 4 simulated temperature distributions within an emitter (width w = 1100 pm) in a 1 cm diode laser bar of the kW class (8 emitters) at 1 kW operating power on a heat sink with a thermal resistance Rth = 0.05 K / W, matching a center emitter with (a) conventional homogeneous and (b) inventive symmetric-inhomogeneous substructure distribution, as well as matching an edge emitter with (c) conventional homogeneous and (d) inventive asymmetric-inhomogeneous substructure distribution;

[0043] Fig. 5 Representations of measured (a) output powers, voltages and conversion efficiencies as a function of the operating current and (b) far-field divergence angles at different operating powers for a 1 cm laser bar of the kW class with conventional homogeneous substructure distribution and two different variants of a 1 cm diode laser bar of the kW class with inventive inhomogeneous substructure distribution at low heat load (thermal resistance R th = 0.02 K / W) and (c), (d) the corresponding measurements at high heat load (thermal resistance Rth = 0.05 K / W).

[0044] Detailed description of the drawings

[0045] Figure 1 shows simulated temperature distributions in a conventional 1 cm diode laser bar of the kW class with 8 emitters (width W = 1100 pm) at different power dissipation, mounted on a heat sink with a thermal resistance of R th= 0.05 K / W. In particular, this is a GaAs-based semiconductor laser. The thermal resistance refers to the change in the average temperature of the active zone relative to the entire pumped area of ​​the laser bar with increasing power loss (heat). To avoid the excitation of undesired lateral modes, the individual emitters of the laser bar have homogeneously substructured contact layers. In the simulation shown only as an example, the structured areas have individual subcontacts, each with a width of 20 pm and a mutual spacing of 9 pm (corresponding to one period p subof 29 pm). The middle 6 emitters (emitters 2 to 7) of the laser bar exhibit symmetrical and largely identical temperature distributions, whereas the outer edge emitters (emitters 1 and 8) of the laser bar exhibit asymmetrical temperature distributions, with a significantly reduced temperature towards the edges of the emitter. At an operating power of 1 kW (corresponding to a power loss of approximately 603 W), the temperature deviation ΔT between the center of the middle emitters and their edges is 4.4 K. For the edge emitters, the deviation even increases to over 10 K. The resulting thermal lensing, which is generated within the individual emitters, gives rise to more higher-order modes and consequently degrades the beam quality of the emitters.Figure 2 shows (a) simulated lateral temperature distributions along a single emitter (width 1 / 1 / = 1100 pm) in a 1 cm kW-class diode laser bar with thermal resistance Rth = 0.05 K / W at 0.6 kW and 1.0 kW operating power and an emitter spacing of d = 255 pm (7 emitters, stronger thermal lens) and d = 65 pm (8 emitters, weaker thermal lens) as well as (b) the measured lateral far-field divergence angles of individual emitters in a 1 cm kW-class diode laser bar with thermal resistance R. th= 0.05 \<J\N und deren Abhängigkeit von der Betriebsleistung bis 1 kW (d = 255 pm mit einem breiteren lateralen Fernfeld und d = 65 pm mit einem schmaleren lateralen Fernfeld). Daran wird die direkte Auswirkung einer reduzierten thermischen Verbiegung (Linsenausbildung) innerhalb der einzelnen Emitter des Laserbarrens auf die Fernfelddivergenz erkennbar. Bei dem Laserbarren mit dem kleineren Emitterabstand haben die Emitter untereinander eine stärkere thermische Wechselwirkung, was einen signifikanten Temperaturabfall im ungepumpten Bereich zwischen den Emittern verhindert und somit eine flachere Temperaturverteilung im Vergleich zu den Emittern im Laserbarren mit dem größeren Emitterabstand bewirken sollte. Dies wird durch die gezeigte Simulation bestätigt (FIG. 2(a)). Die verringerte thermische Linse innerhalb des Emitters verringert die Anzahl und den Divergenzwinkel der lateralen Moden und reduziert den Gesamtstrahldivergenzwinkel deutlich (FIG.2(b)), although the edge emitters (circled in the figure) still have a comparable beam divergence to the emitters in the laser bar with the larger pitch.

[0046] Figure 3 shows a schematic representation of the formation of a structured region 14 with a conventional homogeneous substructure distribution and an inventive inhomogeneous substructure distribution. The contact regions are each formed by a metallic contact layer 10 for the surface contacting of an underlying semiconductor contact layer 12 of an epitaxial layer. In the semiconductor contact layer 12, a structured region 14 with individual subcontacts 16 is formed below the metallic contact layer 10 for the spatial splitting of an operating current that can be supplied via the metallic contact layer 10. The individual subcontacts 16 of a broad-area laser emitter form a substructure distribution. The structured regions 14 shown are illustrated by way of example as part of a laser bar with a plurality of broad-area laser emitters arranged side by side.In the contact area shown with homogeneous substructure distribution according to the state of the art, the width w. SU b and the distance a SU b of the individual subcontacts 16 of the structured region 14 in the semiconductor contact layer 12 below the metallic contact layer 10 is constant in the lateral direction (slow axis). In the illustrated contact region according to the invention with an inhomogeneous substructure distribution, however, the width w varies. SU b and / or the distance a SUb of the individual subcontacts 16 of the structured region 14 in the semiconductor contact layer 12 below the metallic contact layer 10 in the lateral direction (slow axis). An inhomogeneous substructure distribution according to the invention can preferably be achieved by structuring the resistance of the semiconductor contact layer 12 by implanting or doping impurities, or by implementing pn junctions or wide band gap layers. Therefore, the unpumped regions 18 between the individual subcontacts 16 can preferably be ion implantation regions.

[0047] The individual broad-area laser emitters of the laser bar shown are each separated from one another by separation regions 20. These can be formed by appropriate structuring of the epitaxial layers, for example, by deep implantation or appropriate doping with foreign atoms, to increase the electrical resistance in these regions, as well as by etched separation trenches for optical isolation between the individual emitters. The separation regions 20 can extend across the semiconductor contact layer 12 into the underlying epitaxial layers.

[0048] The figure further shows, by way of example, an epitaxial layer system typically used to construct broad-area laser emitters or corresponding laser bars. This comprises a sequence grown on an n-doped substrate 26, comprising an n-doped cladding layer 25, an n-doped waveguide layer 24, a p-doped waveguide layer 22, and a p-doped cladding layer 21. An active layer 23 is formed between the n-doped waveguide layer 24 and the p-doped waveguide layer 22. The semiconductor contact layer 12 is arranged above the p-doped cladding layer 21 and separates it from the metallic (p-side) contact layer 10. Electrical contact with the n-doped substrate 26 can be achieved via an additional n-contact layer 27 (metal contact).

[0049] Figure 4 shows simulated temperature distributions within an emitter (width w = 1100 m) in a 1 cm diode laser bar of the kW class (8 emitters) at 1 kW operating power on a heat sink with a thermal resistance R th = 0.05 K / W, suitable for a center emitter with (a) conventional homogeneous and (b) inventive symmetric-inhomogeneous substructure distribution, as well as for an edge emitter with (c) conventional homogeneous and (d) inventive asymmetric-inhomogeneous substructure distribution. The widths w SUb of the individual subcontacts are shown in the corresponding insets. The temperature deviation ΔT in the structure according to the invention drops to 0.6 K and is thus 7 times lower than in the basic structure with a conventional homogeneous substructure distribution. Due to the more asymmetric temperature distribution in the edge emitters, an asymmetric substructuring with even wider subcontacts than in the central emitter structures is preferably used (cf. Figs. 4(a), 4(c) and 4(b), 4(d)). This reduces the disadvantageous temperature deviation ΔT in the edge emitters to ±1.6 K, which represents a more than 5-fold improvement over the basic structure.

[0050] Figure 5 shows representations of measured (a) output powers, voltages and conversion efficiencies as a function of the operating current and (b) far-field divergence angles at different operating powers for a 1 cm laser bar of the kW class with conventional homogeneous substructure distribution and two different variants of a 1 cm diode laser bar of the kW class with inventive inhomogeneous substructure distribution at low heat load (thermal resistance Rth = 0.02 K / W) as well as (c), (d) the corresponding measurements at high heat load (thermal resistance R th= 0.05 K / W). For these investigations, two different variants of laser bars with a plurality of emitters, which have an inhomogeneous substructure distribution according to the invention (ie a contact area according to the invention), were manufactured and then operated at different heat loads, which were practically achieved by varying the duty cycle. The substructure distributions of variant A correspond to the embodiment described in Figures 4(b) and 4(d). In variant B, the widths of the substructures w SU b increased by 5 pm, without a variation in the period p sub . For comparison, a basic structure with homogeneous substructure distribution according to the embodiment described in Figures 4(a) and 4(c) was also investigated.

[0051] The advantages resulting from the inhomogeneous substructure distribution according to the invention can be observed across the entire operating range investigated. At low heat loads, variant A exhibits a slightly lower efficiency (e.g., ~ 2% efficiency drop at 0.8 kW), but variant B with an increased fill factor F offers a similar efficiency to the basic structure. Furthermore, both variants produce a narrower divergence angle than the basic structure. At high heat loads, both variants deliver higher output power and lower beam divergence than the basic structure across the entire operating range. In particular, a greater advantage arises at the higher operating power, which results in up to 2° lower beam divergence. The highest efficiency is achieved with the substructure distributions of variant B due to a particularly flat temperature profile and larger fill factor F (lower electrical resistance).

[0052] List of reference symbols

[0053] 10 metallic contact layer (e.g. Au contact layer)

[0054] 12 Semiconductor contact layer (e.g. p-doped semiconductor contact layer)

[0055] 14 structured area (of the semiconductor contact layer, e.g. formed by shallow implantation of ions)

[0056] 16 sub-contacts (formed by the structure of the structured area)

[0057] 18 unpumped area (between the individual sub-contacts)

[0058] 20 separation areas (between adjacent broad-area laser emitters of a laser bar, e.g. formed by deep implantation or etched separation trenches)

[0059] 21 p-doped cladding layer

[0060] 22 p-doped waveguide layer

[0061] 23 active layer

[0062] 24 n-doped waveguide layer

[0063] 25 n-doped cladding layer

[0064] 26 n-doped substrate

[0065] 27 n-contact layer (metal contact)

Claims

Patent claims 1. Contact region of a single broad-area laser emitter, comprising: a semiconductor contact layer (12) of an epitaxial layer of the broad-area laser emitter, a metallic contact layer (10) for the planar contacting of the semiconductor contact layer (12), wherein in the semiconductor contact layer (12) for the spatial splitting of an operating current that can be supplied via the metallic contact layer (10), a structured region (14) with individual sub-contacts (16) is formed below the metallic contact layer (10), characterized in that the width w SU b and / or the distance a SU b of the individual subcontacts (16) varies in a lateral direction of the broad-area laser emitter.

2. Contact region according to claim 1, wherein the contact region extends over a lateral strip width W > 150 pm.

3. Contact area according to one of the preceding claims, wherein the width of a sub-contact (16) w SU b is 200 pm.

4. Contact area according to one of the preceding claims, wherein the distance between adjacent sub-contacts (16) a SU b is 50 pm, where the distance a SU b is preferably greater than 1 pm.

5. Contact region according to one of the preceding claims, wherein the period of the sub-contacts (16) p sub varies by less than 10% or the period of the subcontacts (16) psub is constant.

6. Contact region according to one of the preceding claims, wherein a fill factor F of the structured contact layer (14) is between 30% and 95%.

7. Contact area according to one of the preceding claims, wherein the width of the sub-contacts (16) w SU b increases towards the edges and / or the distance between the sub-contacts (16) a SUb decreases towards the edges, whereby the variation of the width w / sub and / or the distance a SU b from the center of the structured area (14) to its edges is preferably at least 10%.

8. Contact area according to one of the preceding claims, wherein the width w SU b and / or the distance a SU b the sub-contacts (16) additionally vary in a longitudinal direction from a front side of the broad-area laser emitter to a back side of the broad-area laser emitter.

9. Contact area according to claim 8, wherein the width of the sub-contacts (16) w SU b increases in the longitudinal direction and / or the distance between the sub-contacts (16) a SU b which decreases in the longitudinal direction, whereby the variation of the width w SU b and / or the distance a SU b from the front of the broad-area laser emitter to the back of the broad-area laser emitter is preferably at least 10%.

10. Contact region according to one of the preceding claims, wherein the contact region is produced by structuring the resistance of the semiconductor contact layer (12) by means of implantation or doping of foreign atoms, or by implementation of pn junctions or wide band gap layers.

11. Broad-area laser emitter comprising a contact region according to one of the preceding claims.

12. A laser bar comprising a plurality of broad-area laser emitters arranged side by side, wherein at least one broad-area laser emitter has a contact region according to one of claims 1 to 10.

13. Laser bar according to claim 12, wherein at least one broad-stripe laser emitter with a contact region according to one of claims 1 to 10 is arranged in the central region of the laser bar and the individual sub-contacts (16) of the broad-stripe laser emitter are formed symmetrically in the lateral direction with respect to the center of the structured region (14).

14. Laser bar according to claim 12 or 13, wherein at least one broad-stripe laser emitter with a contact region according to one of claims 1 to 10 is arranged in the edge region of the laser bar and the individual sub-contacts (16) of the broad-stripe laser emitter are formed asymmetrically in the lateral direction with respect to the center of the structured region (14).

5. Laser bar according to claim 14, wherein the variation of the width w SU b and / or the distance a SUb of the sub-contacts (16) from the center of the structured region (14) towards the central region of the laser bar is smaller than towards the edges of the laser bar, wherein the difference in the variation is preferably at least 10%.

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