Broad-area diode laser with integrated p-n tunnel junction

Abstract

The present invention relates to a broad-area diode laser, BAL, with an integrated p-n tunnel junction. More particularly, the present invention relates to a high-performance broad-area diode laser in which, in order to improve the beam quality and to reduce thermal resistance, a p-n tunnel junction, preloaded in the reverse direction, is integrated in the layer system of the diode laser. A laser diode according to the invention comprises an active layer (20) formed between an n-doped semiconductor material (10, 12, 14) and a p-doped semiconductor material (30, 32, 34), wherein the active layer (20) forms, along a longitudinal axis, an active zone for generating electromagnetic radiation; wherein at least one n-doped intermediate layer (50, 54) is arranged between a overlying p-side metal contact (52) and the p-doped semiconductor material (30, 32, 34), wherein in the at least one n-doped intermediate layer (50, 54) in the region above the active zone, a p-n tunnel junction (40) is formed which is directly adjacent to the p-doped semiconductor material (30, 32, 34).

Description

[0001] Broad-area diode laser with integrated pn tunnel junction

[0002] Description

[0003] The present invention relates to a broad-area diode laser (BAL) with an integrated pn tunnel junction. In particular, the present invention relates to a high-power broad-area diode laser in which a reverse-biased pn tunnel junction is integrated into the layer system of the diode laser to improve beam quality and reduce thermal resistance.

[0004] State of the art

[0005] Broad-area diode lasers can exhibit particularly high efficiency and brilliance. These emitters reliably achieve output powers of >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 the key element of fiber-coupled laser systems designed to deliver high-density beams for materials processing at high conversion efficiencies. To increase the output power of these systems and reduce their costs, it is important to improve the beam quality, especially of the slow axis, as this enables the coupling of a larger number of emitters into low numerical aperture (NA) fibers.

[0006] However, at high optical output powers and the associated operating currents, a significant deterioration in beam quality generally occurs, which has a particularly negative impact on coupling in fibers. It has been shown that thermal lensing (and not carrier- or gain-induced guiding) in the slow axis is one of the predominant causes of beam quality degradation at increased operating current (Bai, JG et al., Mitigation of Thermal Lensing Effect as a Brightness Limitation of High-Power Broad Area Diode Lasers, Proc. SPIE 7953, 79531 F (2011) & Crump, P. et al., Experimental Studies Into the Beam Parameter Product of GaAs High-Power Diode Lasers, IEEE J. Sci. Top. Quantum Electron., vol. 28, no. 1 (2022)).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 region under the laser stripe, which leads to a local increase in the refractive index and thus to additional lateral waveguiding and, as a consequence, to a larger divergence angle.

[0007] In particular, previous studies on GaAs-based broad-area diode lasers (e.g., Rieprich, J. et al., Thermal boundary resistance between GaAs and p-side metal as limit to high power diode lasers, IEEE High Power Diode Lasers and Systems Conf. (Coventry, UK), pp. 35-36 (2019)) have shown that a significant thermal barrier forms at the interface between the highly p-doped GaAs contact layer and the metal contact deposited above it. The reduced heat dissipation caused by this barrier amplifies the effect of the resulting thermal lens, leading to lower beam quality and increased thermal resistance. In contrast, such a thermal barrier could not be detected at the other semiconductor-metal interface within the device, i.e., between n-doped GaAs and metal.

[0008] Disclosure of the invention

[0009] It is therefore an object of the present invention to provide a broad-area diode laser in which the thermal barrier occurring between a highly p-doped contact layer and the metal contact deposited thereon is to be reduced or completely prevented in order to improve the beam quality and to reduce the thermal resistance.

[0010] These objects are achieved according to the invention by the features of independent claim 1. Advantageous embodiments of the invention are contained in the subclaims.

[0011] The present invention relates to a laser diode comprising an active layer formed between an n-doped semiconductor material and a p-doped semiconductor material, wherein the active layer forms an active zone for generating electromagnetic radiation along a longitudinal axis; wherein at least one n-doped intermediate layer is arranged between an overlying p-side metal contact and the p-doped semiconductor material, wherein a pn tunnel junction directly adjacent to the p-doped semiconductor material is formed in the at least one n-doped intermediate layer in the region above the active zone. Preferably, the at least one n-doped intermediate layer comprises a p-side n-contact layer. The p-side metal contact can be arranged on the p-side n-contact layer.The n-doped semiconductor material typically comprises an n-doped substrate (referred to as the n-substrate), an n-sided n-cladding layer arranged on the n-substrate, and an n-waveguide layer arranged on the n-sided n-cladding layer. The p-doped semiconductor material typically comprises a p-waveguide layer and a p-cladding layer arranged on the p-waveguide layer. In the prior art, a p-contact layer is usually arranged on the p-cladding layer. Between the two differently doped semiconductor materials is the active layer, which is designed to generate light. The active zone is the portion of the active layer in which light generation actually occurs through charge carrier injection during operation of the laser diode. The longitudinal axis points in the longitudinal direction and preferably corresponds to the resonator axis of the laser.

[0012] The charge carriers are typically supplied on the n-side via the n-substrate and on the p-side via an overlying metal contact, whereby this p-side metal contact then forms a semiconductor-metal interface with an underlying p-contact layer. As already described above, this interface represents a significant thermal barrier. Since such a thermal barrier could not be detected at an n-sided semiconductor-metal interface, according to the invention at least one n-doped intermediate layer is arranged between the overlying p-side metal contact and the underlying p-doped semiconductor material. In addition, to further enable charge carrier injection, a pn tunnel junction is formed in the at least one n-doped intermediate layer in the region above the active zone, directly adjacent to the p-doped semiconductor material.Thus, a preferred interface between an n-type semiconductor material and a metal can also be realized on the p-side, i.e., without the formation of a significant thermal barrier. The pnT junction preferably has a total thickness of less than 100 nm.

[0013] The present invention is based on the finding that a semiconductor-metal interface with an n-doped semiconductor on both sides of the BAL is particularly advantageous. To achieve this, the p-side contact layer of the BAL can be designed to be n-doped rather than p-doped. However, this creates a reverse-biased pn junction that acts as a current barrier. To avoid this, a reverse-biased pn tunnel junction (TJ) is formed at this pn interface. This tunnel junction consists, for example, of very highly doped semiconductor layers and allows charge carriers to tunnel between a corresponding p-side n-contact layer and the other p-side semiconductor layers.In such a design, it is crucial that the tunnel junction has a very low turn-on voltage and a very low series resistance so that the conversion efficiency of the BAL is not compromised. The BALs according to the invention are also referred to as TJ-BALs.

[0014] In addition to reducing or eliminating the thermal barrier that would otherwise form at the p-side semiconductor-metal interface, this approach offers further advantages. The high electrical conductivity of the highly doped n-contact and TJ layers can lead to very low series resistance between the active region and the epi-side contact, particularly in vertical structures with thin p-side waveguide and cladding layers such as the ETAS design (ETAS - Extreme Triple Asymmetry Structure). The low series resistance leads to higher conversion efficiency, especially at higher currents (Crump, P. et al., Efficient High-Power Laser Diodes, IEEE J. Sci. Top. Quantum Electron., vol. 19, no. 4 (2013)).In addition, the flat TJ layers are so highly doped that they tend towards an equipotential, which means that voltage differences that occur between different areas of the laser chip cannot be maintained and immediately equalize. The low epi-side resistance and the presence of an equipotential have the advantage of reducing spatial hole burning and suppressing higher-order lateral modes, thereby further improving beam quality, output power and conversion efficiency (Zeghuzi, A. et al., Traveling wave analysis of non-thermal far-field blooming in high-power broad-area lasers, IEEE J. Quantum Electron., vol. 55, no. 2 (2019) & Zeghuzi, A. et al., Influence of nonlinear effects on the characteristics of pulsed high-power broad-area distributed Bragg reflector lasers, Opt. Quant. Electron., vol. 50, no. 88 (2018)).

[0015] A further advantage of the very low resistivity of highly n-doped p-side semiconductor layers and the equipotential is that the thickness of the p-side n-contact layer grown over the pn tunnel junction can be significantly increased without a significant deterioration in electrical resistance. This allows the active region in structures with a thin p-side to be protected from process- and design-induced mechanical stresses, which can impair polarization purity, output power, and device lifetime, and lead to unwanted waveguiding, which in turn reduces beam quality.

[0016] Preferably, the pn tunnel junction comprises a p + -Tunnel layer and a layer arranged on top of it +Tunnel layer. Due to the high doping of the two tunnel layers of the pn tunnel junction, the charge carriers can tunnel through the reversely biased pn junction formed at the boundary between the at least one p-side n-doped intermediate layer and the p-doped semiconductor material, so that the electrical resistance during charge carrier injection remains low. The doping concentration of the n- and p-doped layers of the pn tunnel junction is preferably A / D ,A 10 19 cm- 3 (usual doping concentration of the environment up to about 10 18 cm' 3 ).

[0017] Preferably, the pn tunnel junction is arranged on a p-doped sub-contact layer (p-sub-contact layer) of the p-doped semiconductor material. The p-sub-contact layer essentially corresponds to the p-contact layer in the prior art. However, according to the invention, no metal contact is arranged on the p-sub-contact layer; instead, it is separated from the p-sub-contact layer by the at least one n-doped intermediate layer. The p-sub-contact layer can be distinguished from the underlying p-cladding layer either by the semiconductor material or its composition or by a discontinuity in the refractive index / refractive index gradient at the layer boundary.

[0018] The pn tunnel junction is preferably arranged on a p-doped cladding layer of the p-doped semiconductor material. In this case, no p-sub-contact layer is arranged between the p-doped cladding layer and the pn tunnel junction. Preferably, an n-doped cladding layer is arranged on the pn tunnel junction. This means that the p-side cladding layer comprises a p-doped and an n-doped region, between which the pn tunnel junction is arranged. Since the optical modes guided in the waveguide layer also extend into the cladding layers, this means that the optical modes can extend on the p-side beyond the pn tunnel junction into the p-side n-doped cladding layer. Any contact layer that may be adjacent to this, however, no longer plays a significant role in waveguiding.

[0019] Preferably, a stripe width of the diode laser is defined by a lateral width W of the pn tunnel junction. Due to the blocking pn junction that forms everywhere outside the pn tunnel junction, the injection region can be defined by the geometric definition of the pn tunnel junction. Thus, the current path can be defined by the size and shape of the pn tunnel junction.

[0020] Alternatively, the pn-tunnel junction can be formed as a layer, and a stripe width of the diode laser is defined by a lateral width W of an opening of an n-current aperture introduced into the p-doped semiconductor material. In this case, the pn-tunnel junction cancels out the effect of the blocking pn junction over a large area, and structuring of individual stripes must therefore be done by other means. The proposed n-current apertures are sufficiently well known in the prior art for limiting current flow. The current path can thus be defined via the size and shape of the opening of the n-current aperture (aperture opening) in a manner completely analogous to the embodiment described above. The n-current aperture preferably has a total thickness of less than 100 nm, wherein the doping concentration of the n-current aperture is preferably N D 10 18 cm -3 is.

[0021] If the pn tunnel junction is formed as a layer, the stripe width of the diode laser can be defined not via an n-type current gate but also via a lateral width W of a region between two adjacent deep implantation regions (e.g., by ion implantation). Deep implantation can increase the resistance in the treated regions so much that current effectively flows only through the non-deep implanted regions. Preferably, the deep implantation extends from the metal contact into the p-type cladding layer. The series resistance of the deep implantation region is preferably at least twice that of the surrounding region.

[0022] Preferably, the semiconductor material is based on GaAs. For example, an n-substrate may comprise GaAs, an n-side n-cladding layer may comprise AlGaAs, an n-waveguide layer may comprise AlGaAs, a p-waveguide layer may comprise AlGaAs, and a p-cladding layer may comprise AlGaAs. A p-substrate contact layer may comprise GaAs. A pn-tunnel junction may be referred to as a p+ tunnel layer. + -GaAs and as n + -Tunnel layer n + -GaAs. An n-type contact layer may comprise GaAs. A p-side n-type cladding layer may comprise AlGaAs.

[0023] The minimum distance between the active layer and the pn tunnel junction is preferably less than 1.3 pm, more preferably less than 1 pm, and even more preferably less than 0.5 pm. The advantage of keeping the distance between the active layer and the pn tunnel junction as small as possible is the reduction of series resistance and spatial hole burning, thereby improving the laser properties (e.g., beam quality, power, efficiency).

[0024] In the TJ-BALs according to the invention, various lateral patterning techniques can be implemented to limit the current to the center of the device (i.e., below the laser stripes or above the active region). The resulting current limitation minimizes losses at the stripe edges and limits the adverse effects of lateral current spread and lateral carrier accumulation (LCA) on beam quality. Current limitation is more important in these TJ-BALs than in standard BALs because current spread is significantly stronger in an n-contact layer than in a p-contact layer due to the higher mobility of electrons compared to holes.

[0025] The residual layer thickness d res between the active zone and a current aperture is preferably less than 1 pm. By keeping the residual layer thickness d as small as possible resadverse current spreading can be reduced. The residual layer thickness d res In general, this indicates the minimum distance between the active layer and a structure closest to the active layer, which is additionally incorporated into the actual basic structure of the layered structure of the laser diode to determine the stripe width of the diode laser. This can be, for example, a pn tunnel junction according to the invention, an n-type current gate, or a corresponding deep implantation region. The p-side total thickness dtot including the pn tunnel junction and p-side n-type contact layer is preferably greater than 2 pm. The total thickness ÖWL of the waveguide layers is preferably greater than 1 pm. The thickness of the p-side waveguide layer d p -w. is preferably less than 350 nm. A stripe width is preferably greater than or equal to 50 pm. The resonator length L is preferably greater than or equal to 3 mm.

[0026] Further preferred embodiments of the invention result from the features mentioned in the respective subclaims.

[0027] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0028] Brief description of the drawings

[0029] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show:

[0030] Fig. 1 is an exemplary schematic representation of a first embodiment of a laser diode according to the invention,

[0031] Fig. 2 is an exemplary schematic representation of a second embodiment of a laser diode according to the invention,

[0032] Fig. 3 is an exemplary schematic representation of a third embodiment of a laser diode according to the invention,

[0033] Fig. 4 is an exemplary schematic representation of a fourth embodiment of a laser diode according to the invention. Fig. 5 is an exemplary schematic representation of a fifth embodiment of a laser diode according to the invention.

[0034] Fig. 6 is an exemplary schematic representation of a sixth embodiment of a laser diode according to the invention.

[0035] Detailed description of the drawings

[0036] Figure 1 shows an exemplary schematic representation of a first embodiment of a laser diode according to the invention.The laser diode shown comprises an active layer 20 formed between an n-doped semiconductor material (n-substrate 10, n-side n-cladding layer 12, n-waveguide layer 14) and a p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32, p-sub-contact layer 34), wherein the active layer 20 forms an active zone for generating electromagnetic radiation along a longitudinal axis; wherein an n-contact layer 50 is arranged between an overlying p-side metal contact 52 and the p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32, p-sub-contact layer 34), wherein in the n-contact layer 50 in the region above the active zone a pn-tunnel junction 40 is formed directly adjacent to the p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32, p-sub-contact layer 34).The p-n tunnel junction 40 shown comprises a p-type layer arranged on the p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32, p-sub-contact layer 34). + -Tunnel layer 42 and a + Tunnel layer 44. In this embodiment, the pn tunnel junction 40 is arranged on a p-doped sub-contact layer 34 of the p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32, p-sub-contact layer 34). A stripe width of the diode laser is defined by a lateral width W of the pn tunnel junction 40. The remaining layer thickness d res is defined in this embodiment as the minimum distance between the active layer 20 and the p-n tunnel junction 40.

[0037] This embodiment of the invention can be provided via a two-stage epitaxial growth process with an intermediate etching step. In a first growth step, the structure can be grown up to the pn tunnel junction 40. Subsequently, the tunnel junction layers (42, 44) can be selectively etched away outside the stripe. After subsequent epitaxial growth of the n-contact layer 50, a reverse-biased pn junction is formed in the outer regions of the structure, while the central pn tunnel junction 40 permits current flow. This is a known method for current and optical confinement in vertical cavity surface-emitting lasers (VCSELs).

[0038] Figure 2 shows an exemplary schematic representation of a second embodiment of a laser diode according to the invention. The basic layer structure corresponds to the arrangement shown in Fig. 1; the individual reference numerals and their respective assignments therefore apply accordingly. In contrast to the embodiment shown there, however, the pn tunnel junction 40 is formed as a layer, and the stripe width of the diode laser is defined by a lateral width W of an opening of an n-current aperture 60 introduced into the p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32, p-sub-contact layer 34). In particular, in the example shown, the n-current aperture 60 is arranged within the p-sub-contact layer 34. The remaining layer thickness dres in this embodiment is defined as the minimum distance between the active layer 20 and the current aperture 60.

[0039] In this embodiment of the invention, current confinement can also be achieved through a two-step epitaxial process with an intermediate etching step. The current blocking at the component edges is realized independently of the tunnel junction by the so-called (enhanced) self-aligned lateral structure. For this purpose, highly n-doped layers can be integrated near the underside of the p-side contact layer (i.e., the p-subcontact layer 34), creating a blocking pn junction with reversed bias. The first growth step ends after these layers have grown. They can then be selectively etched away in the center to create a corresponding opening for current flow. The remainder of the p-subcontact layer 34, as well as the pn tunnel junction 40 and the n-contact layer 50, can then be grown over the patterned n-current gate 60.

[0040] Figure 3 shows an exemplary schematic representation of a third embodiment of a laser diode according to the invention. The basic layer structure corresponds to the arrangement shown in Fig. 2; the individual reference numerals and their respective assignments therefore apply accordingly. The pn tunnel junction 40 is also formed as a layer here. In contrast to the embodiment shown there, a stripe width of the diode laser is defined via a lateral width W of a region between two adjacent deep implantation regions 70. In particular, in the example shown, the two edge deep implantation regions 70 extend from the metal contact 52 into the p-cladding layer 32. Since the deep implantation regions 70 can also create an opening for the current flow, the additional integration of an n-current aperture 60 is not necessary. The remaining layer thickness d resis defined in this embodiment as the minimum distance between the active layer 20 and the bottom of the deep implantation regions 70.

[0041] In contrast to the previously described embodiments, this embodiment can be realized via single-step epitaxial growth, which reduces the complexity of the manufacturing process and thus its cost. Current limitation is achieved, for example, by deep, high-energy ion implantation at the edges of the device. Furthermore, current flow can be prevented by increasing the series resistance and introducing point defects where charge carriers rapidly recombine. Deep implantation through the active region effectively prevents current spreading and LCA, which could significantly improve beam quality, but also severely impacts power and efficiency. Therefore, an implantation profile tailored to terminate above the active region (e.g., within the p-type cladding layer) is preferred in terms of overall performance.

[0042] Figure 4 shows an exemplary schematic representation of a fourth embodiment of a laser diode according to the invention. The laser diode shown comprises an active layer 20 formed between an n-doped semiconductor material (n-substrate 10, n-side n-cladding layer 12, n-waveguide layer 14) and a p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32). The active layer 20 forms an active zone for generating electromagnetic radiation along a longitudinal axis. wherein an n-contact layer 50 and a p-side n-cladding layer 54 are arranged between an overlying p-side metal contact 52 and the p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32), wherein in the p-side n-cladding layer 54 in the region above the active zone a pnT tunnel junction 40 is formed which directly adjoins the p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32).The pnT junction 40 shown comprises a p-type layer arranged on the p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32). + -Tunnel layer 42 and a + Tunnel layer 44. In this embodiment, the pn tunnel junction 40 is arranged on a p-doped cladding layer 32 of the p-doped semiconductor material (p-waveguide layer 30, p-cladding layer 32). Additionally, an n-doped cladding layer 54 is formed on the pn tunnel junction 40. A stripe width of the diode laser is defined by a lateral width W of the pn tunnel junction 40. The remaining layer thickness d res is defined in this embodiment as the minimum distance between the active layer 20 and the p-n tunnel junction 40.

[0043] The key difference from the embodiment shown in Fig. 1 is that the pnT tunnel junction 40 is arranged on the p-doped cladding layer 32 and thus closer to the active zone. The integration of an additional p-sub-contact layer 34 is eliminated. While this approach to the active zone makes the pn tunnel junction 40 technologically more complex (particularly in variants with two-step epitaxial growth), significant performance advantages can be achieved.

[0044] Figure 5 shows an exemplary schematic representation of a fifth embodiment of a laser diode according to the invention. The basic layer structure corresponds to the arrangement shown in Fig. 4; the individual reference numerals and their respective assignments therefore apply accordingly. The actual functional principle and a possible manufacturing method, however, can be found in Fig. 2. This embodiment differs from the embodiment shown in Fig. 2 only in the position of the tunnel junction 40 and the absence of a p-sub contact layer 34.

[0045] Figure 6 shows an exemplary schematic representation of a sixth embodiment of a laser diode according to the invention. The basic layer structure corresponds to the arrangement shown in Figure 5; the individual reference numerals and their respective assignments therefore apply accordingly. The actual functional principle and a possible manufacturing method, however, can be found in Figure 3. This embodiment also differs from the embodiment shown in Figure 3 only in the position of the tunnel junction 40 and the absence of a p-sub contact layer 34.

[0046] List of reference symbols

[0047] 10 n-substrate (e.g. GaAs)

[0048] 12 n-cladding layer (n-side, e.g. AIGaAs)

[0049] 14 n-waveguide layer (e.g. AlGaAs)

[0050] 20 active layer (includes active zone)

[0051] 30 p-waveguide layer (e.g. AlGaAs)

[0052] 32p cladding layer (e.g. AIGAAs)

[0053] 34 p-sub contact layer (e.g. GaAs)

[0054] 40 pnT tunnel transition

[0055] 42 p + -Tunnel layer (e.g. p + -GaAs)

[0056] 44 n + -Tunnel layer (e.g. n + -GaAs)

[0057] 50 n-(sub-)contact layer (p-side, e.g. GaAs)

[0058] 52 Metal contact (p-side)

[0059] 54 n-cladding layer (p-side, e.g. AIGaAs)

[0060] 60 n-current aperture

[0061] 70 deep implantation area

[0062] W lateral width dres residual layer thickness

Claims

Patent claims 1. Laser diode comprising: an active layer (20) formed between an n-doped semiconductor material (10, 12, 14) and a p-doped semiconductor material (30, 32, 34), wherein the active layer (20) forms an active zone along a longitudinal axis for generating electromagnetic radiation; characterized in that at least one n-doped intermediate layer (50, 54) is arranged between an overlying p-sided metal contact (52) and the p-doped semiconductor material (30, 32, 34), wherein in the at least one n-doped intermediate layer (50, 54) a pn tunnel junction (40) is formed in the region above the active zone, directly adjacent to the p-doped semiconductor material (30, 32, 34).

2. Laser diode according to claim 1, wherein the pnT tunnel junction (40) is a p arranged on the p-doped semiconductor material (30, 32, 34). + -tunnel layer (42) and a n arranged thereon +-T tunnel layer (44) includes.

3. Laser diode according to claim 1 or 2, wherein the pnT tunnel junction (40) is arranged on a p-doped sub-contact layer (34) of the p-doped semiconductor material (30, 32, 34).

4. Laser diode according to claim 1 or 2, wherein the pnT tunnel junction (40) is arranged on a p-doped cladding layer (32) of the p-doped semiconductor material (30, 32, 34).

5. Laser diode according to claim 4, wherein an n-doped cladding layer (54) is arranged on the pn tunnel junction (40).

6. Laser diode according to one of claims 1 to 5, wherein a strip width of the diode laser is defined via a lateral width W of the pn tunnel junction (40).

7. Laser diode according to one of claims 1 to 5, wherein the pn tunnel junction (40) is formed as a layer and has a lateral width W of an opening of a The p-doped semiconductor material (30, 32, 34) introduced by the n-type current aperture (60) defines a strip width of the diode laser. Laser diode according to any one of claims 1 to 5, wherein the pn tunnel junction (40) is formed as a layer and a strip width of the diode laser is defined over a lateral width W of a region between two adjacent depth implantation areas (70). Laser diode according to any one of the preceding claims, wherein the semiconductor material is GaAs-based. Laser diode according to any one of the preceding claims, wherein the minimum distance between the active layer (20) and the pn tunnel junction (40) is less than 1.3 pm.

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