Semiconductor laser with improved beam quality

Abstract

The present invention relates to semiconductor lasers with improved beam quality, and in particular to high performance semiconductor-based laser bars with reduced thermal lensing and reduced lateral far-field divergence due to a non-uniform sub-contact structure in the contact region. The contact region of the claimed single broad-area laser emitter comprises a semiconductor contact layer (12) of the epitaxial layer of the broad-area laser emitter and a metal contact layer (10) for forming a planar surface contact with the semiconductor contact layer (12), wherein a structured region (14) including individual sub-contacts (16) is formed in the semiconductor contact layer (12) below the metal contact layer (10) for spatially dividing the operating current that can be supplied via the metal contact layer (10), and the width w of the individual sub-contacts (16) of the structured region (14) sub and / or interval a sub varies laterally for the broad-area laser emitter.

Description

[Technical Field]

[0001] The present invention relates to semiconductor lasers with improved beam quality, and in particular to high performance semiconductor-based laser bars with reduced thermal lensing and reduced lateral far-field divergence due to a non-uniform sub-contact structure in the contact region. [Background technology]

[0002] High-performance semiconductor lasers with low beam divergence are crucial for many applications. For example, kW-class semiconductor laser bars contain multiple broad-area lasers (BALs) arranged parallel to one another, typically with a lateral stripe width W between 50 μm and 1200 μm. Corresponding laser bars with powers of approximately 2 kW in quasi-continuous operation or 1 kW in continuous operation have already been successfully fabricated (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), pp. 1525-505, 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).

[0003] However, the thermal and temperature profiles within individual emitters and across the entire laser bar present a significant obstacle to achieving higher powers and beam quality (i.e., 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. Sei. Top. Quant. Electron 28(1), p. 1501111, 2021) have shown that significant thermal lensing effects form during laser operation, and the resulting lensing effects become increasingly pronounced with increasing operating powers.

[0004] In this regard, for example, simulated temperature distributions within a 1 cm wide kW-class GaAs laser bar containing eight BAL emitters with a lateral stripe width W of approximately 1100 μm at various power dissipations are shown in Figure 1. To avoid excitation of unwanted transverse modes, the individual emitters in the laser bar have uniformly substructured GaAs contact layers; in this exemplary simulation, these structures include individual subcontacts in the semiconductor contact layer with a width of 20 μm and a spacing of 9 μm (corresponding to a period of 29 μm). The central six emitters of the laser bar (emitters 2–7) exhibit symmetric and nearly identical temperature distributions, while the outermost emitters (emitters 1 and 8) exhibit asymmetric temperature distributions with a significant temperature drop toward the emitter edges. At an operating power of 1 kW (corresponding to a power dissipation of approximately 603 W), the temperature deviation ΔT between the center of the central emitter and its edges is 4.4 K. For the edge emitters (emitters 1 and 8), the deviation between center and edge increases to over 10 K. The resulting thermal lensing effect generated within the individual emitters in the simulated laser bar induces higher order modes, thereby degrading the beam quality of the emitter.

[0005] The prior art describes various approaches to mitigate thermal lensing effects in individual emitters and laser bars to improve BPP, 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 structured metal contacts (A. Bachmann et al., "Recent brightness improvement of 976 nm high-power laser bars," Proc. SPIE 10086, page 1008602, 2017).

[0006] Other approaches to improving the BPP of high-performance lasers or laser bars by flattening the temperature profile within the laser module are based, for example, on modifying the epitaxial layer design (DE 10 2020 133 368 A1) and lateral bar layout, using pedestals (J.G. Bai et al., Proc. SPIE 7953, 79531F-1, 2011), or additional heat input (J.P. Hohimer et al., "Mode control in broad-area diode lasers by thermally induced lateral index tailoring," Appl. Phys. Lett. 52(4), 260-262, 1988). While the prior art measures alone can significantly reduce the thermal lensing effect, further suppression of the thermal lensing effect is necessary to provide even higher powers and further improve beam quality. Summary of the Invention [Problem to be solved by the invention]

[0007] DISCLOSURE OF THE INVENTION

[0008] 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 the thermal lensing effect in individual emitters or laser bars is reduced by changing the lateral temperature profile based on existing epitaxial structures, i.e., without making complex adjustments to the basic epitaxial design or layer structure, in order to improve BPP.

[0009] These objects are achieved according to the invention by the features of independent claims 1, 11 and 12. Advantageous configurations of the invention are contained in the respective dependent claims. In particular, in this respect, the uniform substructure distribution in the contact region of a broad-area laser emitter in a laser bar, which is already known from the prior art (M.J. 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), pp. 1525-505, 2022), is adapted and fundamentally further developed to achieve the stated objects. [Brief explanation of the drawings]

[0010] DETAILED DESCRIPTION OF THE INVENTION

[0011] The contact region of the claimed broad area laser emitter comprises a semiconductor contact layer of the epitaxial layer of the broad area laser emitter and a metal contact layer for forming a planar surface contact with the semiconductor contact layer, wherein a structured region comprising individual sub-contacts is formed in the semiconductor contact layer below the metal contact layer for spatially dividing the operating current that can be supplied via the metal contact layer, and the width w of each sub-contact sub and / or interval a sub varies laterally across the broad area laser emitter (i.e., within a single laser diode along the slow axis). Further provided is a broad area laser emitter having a contact region according to the present invention.

[0012] Broad-area laser emitters are well known in the prior art; the reader is referred to the relevant technical literature. Such semiconductor laser structures comprise epitaxial layers made of differently doped semiconductor materials, with corresponding charge carrier recombination occurring at the boundary between the n-doped and p-doped regions for beam generation. Charge carriers are typically introduced into the epitaxial structure (along the vertical axis of the semiconductor laser) via a metal contact layer. To accommodate the metal contact layer, the epitaxial layer comprises a semiconductor contact layer at its interface with the metal contact layer as an accommodation layer. This layer allows the metal-semiconductor junction to be produced with the lowest possible contact resistance.

[0013] It is also known from the prior art to form substructures formed below a metal contact layer in a semiconductor contact layer (M.J. 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), pp. 1525-505, 2022). This is particularly useful for preventing the excitation of unwanted transverse modes in broad-area laser emitters. However, in the prior art, the substructures are limited to the width w of individual subcontacts in the semiconductor contact layer below the metal contact layer. sub and interval a sub is designed to be constant laterally. Therefore, the distribution of the substructures is uniform. In contrast, in the present invention, a non-uniform distribution of the substructures is created, and the width w of the individual subcontacts in the semiconductor contact layer below the metal contact layer of the laser emitter is sub and / or interval a sub changes horizontally.

[0014] The structured regions with the individual subcontacts can extend (tangentially to the broad-area laser emitter) through, partially, or entirely within the semiconductor contact layer. Furthermore, the structured regions can also extend into one or more underlying epitaxial layers. The structuring results in alternating low-resistivity conductive regions (subcontacts) and high-resistivity regions (blocking regions between adjacent subcontacts in the structured region of a single broad-area semiconductor laser).

[0015] In areas where current is supplied via individual subcontacts (i.e., by individual conductive regions formed in the structured semiconductor contact layer), more heat is generated. If the distribution of regions pumped by current in a structured manner within the laser stripe is changed, the resulting heat distribution within the emitter is also changed, which, according to the present invention, can be used to the positive effect of flattening the thermal lens effect. Therefore, in the present invention, the heat distribution is redistributed by changing the size and relative arrangement of the individual subcontacts of a substructure known per se, which has a uniform substructure distribution within the semiconductor contact layer.

[0016] For example, increasing the width of the individual subcontacts at the ends of the laser stripe allows for higher total currents due to the gradually lower electrical resistance, which in turn results in higher local total power dissipation in the subcontacts. Therefore, the wider subcontacts have a higher overall heat load, increasing the fraction of heat directed toward the ends of the laser stripe. This minimizes the temperature drop at the emitter edges, ultimately resulting in a flatter overall temperature profile.

[0017] As the spacing between the individual subcontacts is further reduced, the pumped regions have greater thermal interaction with each other, which prevents significant temperature drops in the unpumped regions between the pumped regions, and similarly results in a flatter temperature distribution.

[0018] The concept of the present invention is therefore based on the use of non-uniformly structured contact regions to flatten the temperature profile within a single semiconductor laser emitter (also known as a laser stripe, laser diode, broad-area emitter, etc.), thereby reducing lateral beam divergence. In contrast to the uniform, periodically structured contact regions of the prior art, which extend across the entire width of each individual laser stripe within a conventional laser bar (see Figure 1), sub-contacts that become wider toward the emitter's edges are preferably used. This approach can be used to improve the performance and beam quality of both individual emitters with large apertures and laser bars composed of multiple such individual emitters, if the sub-structure distribution is tailored to their thermal profile.

[0019] The contact area of ​​the broad area laser emitter preferably extends over a lateral stripe width W≧150 μm, more preferably W≧200 μm, where W is the lateral stripe width of a single broad area laser emitter. The broad area laser emitter preferably has a longitudinal length L≧2 mm. The width of the sub-contact is preferably w sub ≦200 μm, more preferably w su <50 μm.

[0020] The spacing between adjacent sub-contacts is preferably a sub ≦50 μm, more preferably a sub <20 μm, more preferably a sub The spacing between adjacent sub-contacts of the sub-structure is preferably <10 μm. sub >1 μm. Such a minimum spacing allows for simplified implementation of structures, for example with photoresist. By reducing the spacing between adjacent sub-contacts, a higher fill factor F can be achieved in the sub-structure, thereby preventing losses (e.g., due to increased electrical series resistance).

[0021] Subcontact period psub Ha, w sub and a sub Using p sub =w sub +a sub Preferably, in a single broad-area laser emitter, p sub varies by less than 20%, more preferably by less than 10%, and even more preferably, all sub-contacts and spacing a sub For p sub are identical.

[0022] The fill factor F of the substructure is preferably between 30% and 95%, more preferably between 60% and 95%, where F is the sum of the pumped area (i.e., the total width of all n subcontacts, n × w sub ) and the total width W of an individual emitter (the width of all subcontacts and their spacing), F = (n × w sub ) / W.

[0023] Preferably, the width w of the subcontact in the semiconductor contact layer below the metal contact layer sub increases towards the edge of the structured region, and / or the spacing a of the subcontacts in the semiconductor contact layer below the metal contact layer sub decreases toward the edge of the structured region, and the width w sub and / or interval a sub The change in width is preferably at least 10%. In this context, "width change" 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 edges of the emitter. Similarly, "spacing change" 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 edges of the emitter.

[0024] Preferably, the width w of the sub-contact in the semiconductor contact layer below the metal contact layer sub and / or interval a subis further varied in the longitudinal direction from the front surface of the broad area laser emitter to the rear surface of the broad area laser emitter. In this case, preferably, the width w of the sub-contact is sub increases in the longitudinal direction, and / or the spacing between the subcontacts a sub decreases longitudinally, and the width from the front to the rear of the broad-area laser emitter, w sub and / or interval a sub The change in the width of the sub-contacts along the cavity axis is preferably at least 10%. Such a change in the sub-structure along the cavity axis can be used primarily to equalize longitudinal temperature fluctuations. In particular, to reduce the current and lower the local temperature, the individual sub-contacts under the metal contact layer on the front surface of the broad-area laser emitter can be made at least 10% narrower than those on the rear surface of the broad-area laser emitter.

[0025] The contact regions according to the invention are preferably produced by structuring the resistance of the semiconductor contact layer by implantation or doping with foreign atoms or by forming a pn junction, for example by two-step epitaxy or by incorporating a layer with a wide band gap. Thus, a 100-fold increase in electrical resistance is preferably achieved in the implanted or doped region. The substructures are preferably 2 μm > d res The metal contact layer can be produced using implantation and / or epitaxial overgrowth techniques, with a typical residual layer thickness of >0 μm. In this case, the residual layer thickness refers to the distance between one surface of the active layer (e.g., its upper surface) and the surface of the implanted / doped region facing the active layer (e.g., its lower surface). The metal contact layer can preferably be an electroplated gold layer (Au) on at least one metal alloy stack (e.g., Ti / Pt / Au).

[0026] Another aspect of the invention relates to a laser bar comprising a plurality of broad area laser emitters arranged adjacent to one another, at least one of the broad area laser emitters being formed with a contact region according to the invention. Preferably, all broad area laser emitters of the laser bar are formed with a contact region according to the invention. In this case, a typical bar width W LB In an exemplary laser bar of .times..times.1 cm, approximately 5 to 80 individual emitters may be preferably arranged, depending on the particular design.

[0027] At least one broad area laser emitter having a contact region according to the invention is preferably arranged in the central region of the laser bar, the individual sub-contacts of which broad area laser emitter are formed laterally symmetrically to the center of the structured region. All broad area laser emitters arranged in the central region of the laser bar preferably have a contact region according to the invention, the individual sub-contacts of which are formed laterally symmetrically to the center of the structured region.

[0028] At least one broad-area laser emitter having a contact region according to the invention is preferably arranged in the end region of the laser bar, the individual sub-contacts of which broad-area laser emitter are formed asymmetrically in the lateral direction relative to the center of the structured region. All broad-area laser emitters arranged in the end region of the laser bar preferably have a contact region according to the invention, the individual sub-contacts of which are formed asymmetrically in the lateral direction relative to the center of the structured region.

[0029] Sub-contact width w sub and / or interval a sub The variation of from the center of the structured region towards the central region of the laser bar is preferably less than the variation towards the edge of the laser bar, and the difference in variation is preferably at least 10%.

[0030] For example, in the eight-emitter 1 cm diode laser bar shown in FIG. 1, the central emitters (emitters 2-7) have a symmetrical temperature distribution, so the sub-contacts of the individual broad-area laser emitters should preferably be symmetrically positioned such that the contact regions according to the present invention are on either side of the center of each corresponding emitter. In this case, the width w of the sub-contacts towards both ends of the corresponding emitter is sub Similarly, the spacing a between the sub-contacts towards both ends of the corresponding emitter sub is preferably symmetrically and monotonically decreasing.

[0031] In this case, the width of the sub-contact from the center to the edge of the corresponding emitter, w sub and / or between sub The change in should preferably be at least 10%. Such non-uniform subcontacts having a symmetrical arrangement with respect to the center of the corresponding emitter are preferably used in the central emitters of a laser bar, which typically comprise at least 30% of the total emitters in the laser bar.

[0032] However, because the end emitters (emitters 1 and 8) shown in Figure 1 have a very asymmetric temperature profile (larger fluctuations at the outer ends) compared to the central emitters, the subcontacts should preferably be positioned asymmetrically on both sides as well. The width w of the subcontact should be asymmetrically positioned on both sides, since the temperature drop on one side is much larger than the other. sub and / or interval a sub The variation in should also preferably start from the center of the emitter and be greater on this side.

[0033] For edge emitters, the temperature drop is greater, the width of the subcontact from the center to the outer edge of the emitter, w sub and / or interval a sub The variation in the width of the sub-contact on the opposite side of the emitter, w, should preferably be at least 20%. sub and / or interval asub The variation in should preferably be smaller. Such non-uniform subcontacts with asymmetric placement relative to the center of the corresponding emitter should preferably be used on emitters near the edges of the laser bar, which typically comprise at least 1 and up to about 35% of all emitters on each side of the laser bar.

[0034] Further preferred embodiments of the invention are evident from the features set forth in the dependent claims.

[0035] The different embodiments of the invention described in this application can be advantageously combined with one another, unless otherwise specified.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The invention will now be described in exemplary embodiments with reference to the accompanying drawings.

[0038] Figure 1 shows the thermal resistance R th Figure 1 shows the simulated lateral temperature distribution in a conventional kW-class 1 cm diode laser bar with eight emitters (width W = 1100 μm) at different power dissipations on a heat sink with a .DELTA.=0.05 K / W.

[0039] Figure 2 shows (a) the thermal resistance R at operating powers of 0.6 kW and 1.0 kW, and emitter spacing d = 255 μm (7 emitters, greater thermal lensing effect) and d = 65 μm (8 emitters, weaker thermal lensing effect). th Simulated lateral temperature distribution along a single emitter (width W = 1100 μm) in a kW-class 1 cm diode laser bar with ω = 0.05 K / W, and (b) thermal resistance R th We show the measured lateral far-field divergence angles of individual emitters in a kW-class 1 cm diode laser bar with d = 0.05 K / W and its dependence on operating power up to 1 kW (with a wider lateral far-field d = 255 μm and with a narrower lateral far-field d = 65 μm).

[0040] FIG. 3 is a schematic diagram for forming substructures having a conventional uniform substructure distribution and a non-uniform substructure distribution according to the present invention.

[0041] FIG. 4 shows the thermal resistance R corresponding to a center emitter with (a) a conventional uniform substructure distribution and (b) a symmetric non-uniform substructure distribution according to the present invention, and an edge emitter with (c) a conventional uniform substructure distribution and (d) an asymmetric non-uniform substructure distribution according to the present invention. th Figure 1 shows the simulated temperature distribution within the emitters (width w = 1100 μm) of a kW-class 1 cm diode laser bar (8 emitters) at an operating power of 1 kW on a heat sink of 0.05 K / W.

[0042] Figure 5 shows the low heat load (thermal resistance R th = 0.02 K / W) and two different variants of kW-class 1 cm diode laser bars with a conventional uniform substructure distribution and with a non-uniform substructure distribution according to the present invention. (a) Measured output power, voltage, and conversion efficiency depending on the operating current, and (b) far-field divergence angle at different operating powers are shown. (c) and (d) are plots of the thermal resistance R th The corresponding measurements at 0.05 K / W are shown.

[0043] Detailed Description of the Drawings

[0044] Figure 1 shows the thermal resistance R thFigure 1 shows the simulated lateral temperature distribution of a conventional kW-class 1 cm diode laser bar with eight emitters (width W = 1100 μm) mounted on a heat sink with a power dissipation of 0.05 K / W, at different power dissipations. In particular, this is a GaAs-based semiconductor laser. The thermal resistance is related to the change in the central temperature of the active region based on the total pumping surface area of ​​the laser bar with increasing power dissipation (heat). To avoid excitation of unwanted transverse modes, the individual emitters of the laser bar have uniformly sub-structured contact layers; in the simulations shown purely as examples, the structured regions are each 20 μm wide and spaced 9 μm apart (with a periodicity of 29 μm). sub The central six emitters of the laser bar (emitters 2-7) exhibit symmetric and nearly identical temperature distributions, whereas the outer edge emitters of the laser bar (emitters 1 and 8) exhibit an asymmetric temperature distribution with a significant drop in temperature towards the emitter's edge. 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 central emitter and its edge is 4.4 K. For the edge emitters, the deviation increases to over 10 K. The resulting thermal lensing effect generated within the individual emitters induces higher-order modes and therefore degrades the emitter's beam quality.

[0045] Figure 2 shows (a) the thermal resistance R th Simulated lateral temperature distribution along a single emitter (width W = 1100 μm) in a kW-class 1 cm diode laser bar with θ = 0.05 K / W, operating powers of 0.6 kW and 1.0 kW, and emitter spacing d = 255 μm (7 emitters, greater thermal lensing effect) and d = 65 μm (8 emitters, weaker thermal lensing effect), and (b) thermal resistance R thFigure 2(a) shows the measured transverse far-field divergence of individual emitters in a kW-class 1 cm diode laser bar with a d = 0.05 K / W and its dependence on operating power up to 1 kW (with a wider transverse far-field d = 255 μm and a narrower transverse far-field d = 65 μm). This figure identifies the direct effect of reduced thermal distortion (lensing) within the individual emitters of the laser bar on the far-field divergence. Laser bars with smaller emitter spacing exhibit greater thermal interactions between emitters, which should prevent significant temperature drops in the unpumped regions between pumped regions compared to emitters in laser bars with larger emitter spacing, resulting in a flatter temperature distribution as well. This is confirmed by the simulations shown (Figure 2(a)). The reduction of thermal lensing within the emitters reduces the number of transverse modes and their divergence angles, significantly reducing the total beam divergence (Figure 2(b)). However, the edge emitters (shown as circles in the figure) still have beam divergence comparable to the emitters in the laser bar with large emitter spacing.

[0046] FIG. 3 shows a schematic diagram for forming a structured region 14 with a uniform substructure distribution according to the prior art and a non-uniform substructure distribution according to the present invention. Here, each contact region is formed by a metal contact layer 10 for forming a planar surface contact with the semiconductor contact layer 12 of the underlying epitaxial layer. To spatially divide the operating current that can be supplied via the metal contact layer 10, a structured region 14 with individual subcontacts 16 is formed in the semiconductor contact layer 12 below the metal contact layer 10. In this case, the individual subcontacts 16 of the broad-area laser emitters form the substructure distribution. The structured region 14 shown is shown by way of example as part of a laser bar with multiple broad-area laser emitters arranged adjacent to one another. In the illustrated contact region with a uniform substructure distribution according to the prior art, the width w of the individual subcontacts 16 of the structured region 14 is 1 / 2 sq. m. sub and interval a subare constant in the lateral direction (slow axis) within the semiconductor contact layer 12 below the metal contact layer 10. However, in the illustrated contact region with a non-uniform substructure distribution according to the present invention, the width w of the individual subcontacts 16 in the structured region 14 sub and / or interval a sub varies laterally (slow axis) in the semiconductor contact layer 12 below the metal contact layer 10. The non-uniform substructure distribution according to the present invention can be preferably implemented by structuring the resistance of the semiconductor contact layer 12 by implanting or doping with foreign atoms or by forming a pn junction or a layer with a wide bandgap. The non-pumped regions 18 between the individual subcontacts 16 can therefore preferably be ion-implanted regions.

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

[0048] The figure also shows, by way of example, an epitaxial layer system typically used to construct broad-area laser emitters or corresponding laser bars. It includes a sequence grown on an n-doped substrate 26, including 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. A semiconductor contact layer 12 is disposed on top of the p-doped cladding layer 21 and separates it from the metal (p-side) contact layer 10. The n-doped substrate 26 can be electrically contacted via an additional n-contact layer 27 (metal contact).

[0049] FIG. 4 shows the thermal resistance R corresponding to a center emitter with (a) a conventional uniform substructure distribution and (b) a symmetric non-uniform substructure distribution according to the present invention, and an edge emitter with (c) a conventional uniform substructure distribution and (d) an asymmetric non-uniform substructure distribution according to the present invention. th Figure 1 shows the simulated temperature distribution within the emitters (width w = 1100 μm) of a kW-class 1 cm diode laser bar (8 emitters) at 1 kW operating power on a heat sink with a λ = 0.05 K / W. In this case, the width of each individual subcontact w sub is shown in the corresponding inset. In the structure according to the present invention, the temperature deviation ΔT is reduced to 0.6 K, thus 7 times lower than in the basic structure with a conventional uniform substructure distribution. Due to the stronger asymmetric temperature distribution in the edge emitters, asymmetric substructures with even wider subcontacts are preferably used for these edge emitters than in the central emitter structure (see Figures 4(a), 4(c) and 4(b), 4(d)). This reduces the unfavorable temperature deviation ΔT in the edge emitters to ±1.6 K, which corresponds to an improvement of more than 5 times compared to the basic structure.

[0050] Figure 5 shows the low heat load (thermal resistance R th = 0.02 K / W) and two different variants of kW-class 1 cm diode laser bars with a conventional uniform substructure distribution and with a non-uniform substructure distribution according to the present invention. (a) Measured output power, voltage, and conversion efficiency depending on the operating current, and (b) far-field divergence angle at different operating powers are shown. (c) and (d) are plots of the thermal resistance R th =0.05 K / W). For these tests, two different variants of a laser bar with multiple emitters having a non-uniform substructure distribution according to the invention (i.e., having contact regions according to the invention) were fabricated and then operated at different heat loads, which were achieved in practice by varying the operating time. The substructure distribution of variant A corresponds to the embodiment described in Figures 4(b) and 4(d). In variant B, the substructure width w sub is the period p subFor comparison, a base structure with a uniform substructure distribution was also tested according to the embodiment described in Figures 4(a) and 4(c).

[0051] The advantages of the present invention resulting from the non-uniform substructure distribution can be observed here across the entire operating range tested. While variant A has a slightly lower efficiency at low thermal loads (e.g., approximately 2% efficiency reduction at 0.8 kW), variant B, with its 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 thermal loads, both variants offer higher output power and lower beam divergence than the basic structure across the entire operating range. In particular, the greater advantage arises at higher operating powers, leading to a beam divergence that is up to 2° lower. Here, the flat substructure distribution of variant B results in a particularly flat temperature profile and a larger fill factor F (lower electrical resistance), achieving the highest efficiency. [Explanation of symbols]

[0052] 10 Metal contact layer (e.g., Au contact layer) 12 Semiconductor contact layer (e.g., p-doped semiconductor contact layer) 14 Structured area (semiconductor contact layer, e.g. formed by planar implantation of ions) 16 Sub-contact (formed by the structure of the structured area) 18 Non-pumping regions (between individual subcontacts) 20 Isolation regions (between adjacent broad-area laser emitters in a laser bar, e.g., formed by deep implantation or etched trenches) 21 p-doped cladding layer 22 p-doped waveguide layer 23 Active layer 24 n-doped waveguide layer 25 n-doped cladding layer 26 n-doped substrate 27 n-contact layer (metal contact)

Claims

1. A contact region of a single broad area laser emitter, a semiconductor contact layer (12) of the epitaxial layer of the broad area laser emitter; a metal contact layer (10) for forming a flat surface contact with the semiconductor contact layer (12); a structured region (14) containing individual sub-contacts (16) is formed in the semiconductor contact layer (12) below the metal contact layer (10) for spatially dividing an operating current that can be supplied via the metal contact layer (10); The width w of each sub-contact (16) ｓｕｂ and / or interval a ｓｕｂ varies laterally across said broad area laser emitter.

2. The contact region of claim 1 , wherein the contact region extends across a lateral stripe width W≧150 μm.

3. The width of the sub-contact (16) is w ｓｕｂ 3. The contact region according to claim 1 or claim 2, wherein the thickness is ≦200 μm.

4. The contact region according to any one of claims 1 to 3, The spacing between adjacent sub-contacts (16) is a ｓｕｂ ≦50 μm, The interval a ｓｕｂ Preferably, the contact area is greater than 1 μm.

5. The period p of the sub-contacts (16) ｓｕｂ changes by less than 10%, or the period p ｓｕｂ 5. The contact region according to claim 1, wherein the distance is constant.

6. The contact area according to any one of claims 1 to 5, wherein the structured contact layer (14) has a fill factor F of 30% to 95%.

7. The contact region according to any one of claims 1 to 6, The width w of the sub-contact (16) ｓｕｂ increases towards the end, and / or the spacing a of the sub-contacts (16) ｓｕｂ decreases towards the end, The width w from the center of the structured area (14) to its edge ｓｕｂ and / or interval a ｓｕｂ The change in the contact area is preferably at least 10%.

8. The width w of the sub-contact (16) ｓｕｂ and / or interval a ｓｕｂ The contact region of any one of claims 1 to 7, wherein the thickness of the contact region varies further longitudinally from the front surface of the broad area laser emitter towards the rear surface of the broad area laser emitter.

9. 9. The contact region of claim 8, The width w of the sub-contact (16) ｓｕｂ increases in the longitudinal direction, and / or the spacing a of the sub-contacts (16) ｓｕｂ decreases in the longitudinal direction, Width w from the front surface of the wide area laser emitter to the rear surface of the wide area laser emitter ｓｕｂ and / or interval a ｓｕｂ The change in the contact area is preferably at least 10%.

10. 10. The contact region according to claim 1, wherein the contact region is produced by structuring the resistance of the semiconductor contact layer (12) by implanting or doping with foreign atoms or by forming a pn junction or a layer with a wide band gap.

11. A broad area laser emitter comprising a contact region according to any one of claims 1 to 10.

12. A laser bar comprising a plurality of broad area laser emitters arranged adjacent to one another, at least one broad area laser emitter comprising a contact region according to any one of claims 1 to 10.

13. 13. The laser bar of claim 12, At least one broad area laser emitter having a contact region according to any one of claims 1 to 10 is arranged in the central region of the laser bar, A laser bar, wherein the individual sub-contacts (16) of the broad area laser emitter are designed to be laterally symmetrical with respect to the center of the structured region (14).

14. 14. The laser bar according to claim 12 or claim 13, At least one broad-area laser emitter having a contact region according to any one of claims 1 to 10 is arranged in the end region of the laser bar, A laser bar, wherein the individual sub-contacts (16) of the broad area laser emitter are formed asymmetrically in the lateral direction relative to the center of the structured region (14).

15. 15. The laser bar of claim 14, The width w of the sub-contact (16) ｓｕｂ and / or interval a ｓｕｂ the change from the center of the structured area (14) towards the central area of ​​the laser bar is smaller than the change towards the edge of the laser bar, A laser bar, wherein said difference in variation is preferably at least 10%.

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