WO2015106972A1 - Semiconductor laser with anisotropic heat dissipation - Google Patents

Abstract

The invention relates to a semiconductor laser comprising: a laser element (1); a first heat spreading body (14) with anisotropic heat conductivity having the lowest heat conductivity in a direction z'; and a first heat sink (17) wherein the laser element has a first contact surface (2) that is in thermal contact with a heat inlet surface of the first heat spreading body, wherein the heat inlet surface (15) of the first heat spreading body has a first surface normal n, and wherein the first heat spreading body also has a heat outlet surface (16) that is in thermal contact with a heat-absorbing surface (18) of the first heat sink. According to the invention, a direction z' of the lowest heat conductivity of the first heat spreading body comprises a first angle α of greater than 5° in relation to the surface normal n of the heat inlet surface of the first heat spreading body.

Description

 Semiconductor laser with anisotropic heat dissipation

The invention relates to a semiconductor laser, which can be preferably designed as a diode laser bar with one or more emitters and is equipped with measures that allow efficient dissipation of the waste heat and also an improved electrical contact

guarantee.

State of the art

 Numerous measures for cooling diode laser bars are described in the literature in which elements are present which simultaneously serve to supply power and to dissipate heat.

The isotropic heat spreading with metal bodies is known, for example, from DE 10 2008 026 229 A1 and from US Pat. No. 8,486,766 B1. The heat spreader serve simultaneously as electrical

Contact elements. These heat spreader made of metals such as copper or tungsten copper are used. Likewise, metal-coated ceramic bodies are known. Such

Heat spreader made of metal or ceramic have a low elasticity, so that mechanical stresses can occur in the laser element. In addition, the thermal conductivity is limited. For example, copper has a thermal conductivity of less than 400W / (m * K). To reduce mechanical stresses also often a ductile indium layer must be provided. An indium coating is complicated and expensive.

Furthermore, from US 8,340, 144B1 the assembly of diode laser elements with pyrolytic

Carbon foil known. Pyrolytic carbon foil contains highly oriented graphite oriented so that the c direction points to the graphite structure in the direction of the surface normal. In the following, the c-direction is understood to be the direction in which the graphite has the lowest

Having thermal conductivity. One can define an a-direction perpendicular to the c-direction, and a b-direction perpendicular to a and c. It is known that graphite has a hexagonal crystal structure, which has a uniformly very high thermal conductivity in the ab plane, which is also referred to as a basal plane. Ab plane as the plane is referred to, in which the hexagonal rings are composed of carbon atoms, that is the _position of the graphene layers. Because the c-direction of the

Graphite components is highly oriented in the direction of the surface normal of the carbon film, the carbon film is in the direction of the surface normal, ie by the thickness d of the film, poor thermal conductivity. This direction of least thermal conductivity is referred to below as the z ^' direction. For the sake of completeness, it should be noted that this means that it is

CONFIRMATION COPY the preferred direction of the graphite components is. In the case of the above-mentioned mounting technology according to US Pat. No. 8,340,144 B1, it is disadvantageous that a heat spread takes place mainly in the film plane and the heat transmission through the film is poor, since this direction corresponds to the c direction of the graphite. In addition, the electrical conductivity of the carbon film in the c direction is also poor. Since the flow of current to the laser element is via the carbon foil, a voltage drop occurs across the thickness of the carbon foil, which leads to an increased electrical power loss. Therefore, unnecessary waste heat is generated. As a countermeasure, the carbon film is selected as thin as possible, for example 25 μιη. But also the desired effect of heat spreading is suboptimal low pronounced. It is also intended, the graphite foil during assembly of the laser

compress. The compressibility of the carbon film is a poorly reproducible

Property. There may be a bending of the laser bar, an effect referred to in the literature as "smile." In addition, the long term stability of the emitter location may be poor if the film shows subsidence over an extended period of time

Uncertainties, it is difficult to supply the laser radiation to an optical system.

From US 201 1 / 0133236A1 a light-emitting component is known which contains a layer of anisotropic graphite. This graphite layer is oriented so that the c direction, i. H. the direction of least thermal conductivity is oriented in the direction of the surface normal. A disadvantage of this mounting technology is that a heat spread occurs mainly in the layer plane and the heat transfer through the graphite layer is poor, since this direction of the c

Direction of the graphite corresponds. In addition, the electrical conductivity of the graphite layer in the c direction is also poor. Since the flow of current to the laser element is via the graphite layer, a voltage drop occurs across the thickness of the graphite layer, resulting in an increased electrical

Power loss leads. Therefore, unnecessary waste heat is generated.

From DE 10 201 1055 891 A1 is a semiconductor laser diode with a structured

Metallization layer known. By structuring the metallization layer, heat dissipation is allowed to vary along a longitudinal or lateral direction. The metal as a layer material has a material-related isotropic thermal conductivity. Due to the structuring, the thermal conductivity can be reduced in certain areas or directions. This has the disadvantage that the heat dissipation is deteriorated overall. The thermal bonding surface of the diode laser bar can be reduced, which is the

Limits performance of the component. In addition, the structuring is complicated and requires additional process steps in semiconductor manufacturing. Objects of the invention are the disclosure of a method for the efficient removal of the waste heat of a semiconductor laser and the specification of a semiconductor laser with efficient removal of the waste heat. Another equally important task is to ensure an efficient power supply to the semiconductor laser. In addition, the laser element should be as small as possible

have mechanical stresses. In addition, the object of the invention can additionally

Design of the temperature distribution in the semiconductor chip, so that the formation of thermal lenses in the semiconductor laser is minimized. In addition, the semiconductor laser should be long-term stable. A method for producing the heat spreader is to be specified, which is a high

Long-term stability when used in the semiconductor laser allows.

The object is achieved by a semiconductor laser comprising a laser element, a first heat spreader having anisotropic thermal conductivity, which has a lowest thermal conductivity in a direction z ^' , and a first heat sink, wherein the laser element is a first

Contact surface which is in thermal contact with a heat input surface of the first heat spreader and the heat input surface of the first heat spreader has a first surface normal n and the first heat spreader further comprises a heat exit surface which is in thermal contact with a heat receiving surface of the first heat sink. According to the invention, a direction z ^'of the lowest thermal conductivity of the first closes

Heat spreader a first angle a of more than 5 ° to the surface normal n of

Heat input surface of the first heat spreader.

The solution of the problem further comprises a method for heat dissipation of a

Laser element by means of a heat spreader with anisotropic thermal conductivity, which has a heat input surface with a surface normal n. In this method, the direction of least thermal conductivity of the heat spreader at an angle of more than 5 ° to

Surface normal n arranged.

The solution to the problem further comprises a method for reducing or eliminating the compressibility of pyrolytic graphite with anisotropic thermal conductivity for use as a heat spreader with the following steps:

 Preparation of pyrolytic graphite with two parallel surfaces,

 Applying a uniaxial static or dynamic pressure from one to the other surface of the pyrolytic graphite,

Removal of uniaxial pressure

Production of the heat spreader with a heat input surface of the pyrolytic graphite wherein the maximum of the uniaxial static or dynamic pressure exceeds by at least three times the compressive force introduced by a frictional connection on the heat input surface.

The invention enables the efficient removal of the waste heat of a semiconductor laser. In the case of an electrically pumped semiconductor laser (diode laser) is at the same time an efficient

 Power supply to the semiconductor laser guaranteed. The electrical power loss of the diode laser is reduced compared to known methods for mounting with graphite-containing Wärmeleitfolien. The laser element has only low mechanical stresses. In addition, the

Temperature distribution can be optimized in the semiconductor chip. As a result, the divergence of the laser radiation in the waveguide plane, which is also referred to as "slow axis" divergence, can be reduced, Compared with known methods which use a structured layer of isotropic material for heat dissipation, the use according to the invention of the anisotropic material worsens The laser element may comprise one or more gain regions, in which an optical amplification takes place, which leads to the formation of laser radiation, which profit regions may be electrically pumped The laser element may be designed in such a way that in the gain ranges only for photons in a specific direction a reinforcement takes place, which is referred to as the longitudinal direction In the laser element, therefore, there is a longitudinal direction y, which is defined by the fact that only for photons that move in this direction or in the

opposite direction -y propagate, a gain takes place, which leads to the formation of laser radiation. Radiation traveling in the other direction is to a lesser extent or not amplified and / or decoupled from the resonator. The laser element may be a gain guided laser element. The profit areas can be laterally, d. H. transversal, bounded by unpumped areas. The profit areas can be pumped electrically. They can be located in an epitaxially produced on a substrate layer sequence, wherein the layer sequence an active layer (quantum trench), the between two light-guiding layers

(cladding) is arranged. By way of example, the substrate may have a thickness of between 50 μm and 200 μm, while the layer sequence may be, for example, between 3 μm and 20 μm thick. The layer sequence can be designed as a pn junction. The profit ranges can be defined by a structured isolation layer. Only in the recesses in which the

Insulation layer is broken, a current flow through the layer sequence can occur. As a result, only these areas are pumped and can act as profit areas. The profit ranges are therefore determined by local distribution of the operating current (current confinement). The Laser element may be in the longitudinal direction, for example, 0.5 mm to 6 mm long. However, the laser element can also be embodied as a ridge waveguide or as an index-guided laser. The laser element may, for example, be a diode laser bar with one or more emitters. The individual emitters are then the profit areas of the laser element, with the possible exception of any unpumped areas. Profit areas are thus the areas in which an optical amplification takes place so that laser radiation is generated. A diode laser bar with only one emitter is also referred to as a single emitter. The term diode laser bar in the following expressly includes single emitter. The emitters may preferably be designed as broad-band emitters. The laser element, for example a diode laser bar, can have a plurality of profit regions which are parallel to one another, wherein the individual profit regions can be offset in an offset direction perpendicular to the longitudinal direction x and in each case one and the same

Center distance p can have. The width of the profit regions may be, for example, between 5 pm and 200 pm in the transverse direction x, while the distance p may be, for example, 20 pm to 500 pm. The width of the laser element results from the number and width of the profit regions, as well as their distance from one another. The width of the laser element in the transverse direction may be, for example, 0.5 mm to 10 mm. The laser element may preferably be formed as edge emitter. The emission direction of the radiation emitted by the laser element can correspond to the longitudinal direction y of the laser radiation in the laser element. However, a beam deflection can also be provided in the laser element, so that the direction of the laser radiation outside the laser element can deviate from the longitudinal direction of the laser radiation in the gain range of the laser element. The laser element may additionally contain lattice structures, for example known DBR or DFB gratings. The laser element can be electrically pumped and can be operated with a high current. The operating current can be, for example, 1 A to 1000 A. The individual emitter regions can be preferred as wide-band emitter or as

Web waveguide or be designed as a trapezoidal laser. However, the laser element can also be designed as a vertical resonator structure (VCSEL). In addition to or between the gain ranges of a laser element can be unpumped areas that are not flowed through by the operating current. These can be covered, for example, with an insulating masking layer.

The laser element may be terminated with mirrors, for example a high-reflectance mirror layer may be attached to the back facet of the laser element and a low one on the opposite exit-side facet containing the exit aperture reflective mirror layer with a Refelxionsgrad of, for example, 0, 1% to 10%. The mirrors can define a laser resonator that enables laser operation. The laser element can also be designed as a profit element, which is provided only in cooperation with an external resonator for laser operation. In this case, for example, a

be provided by the external resonator wavelength dependent feedback, the

Determining the wavelength of the laser is used. Such an electro-optical gain element is also to be understood as a laser element in the sense of the invention.

The laser element has a first contact surface, which is used for thermal contacting of the

Laser element is used. The first contact surface can also be used for electrical contacting of the

 Serve laser element. In this case, the laser element may have a second contact surface, which serves for making electrical contact with the other electrode of the laser element. This can, but does not have to, also be used for thermal contacting. In a laser bar with known p-side heat dissipation (p-side-down), the first contact surface may be the epitaxial-side electrode of the laser chip, the second contact surface, the opposite substrate-side electrode of the laser chip. The first contact surface may therefore be the anode of a laser diode. The second

Contact surface can be the cathode.

The first contact surface of the laser element may comprise a metal layer in a preferred embodiment of the invention. The metal layer may, for example, preferably be applied flat on the p-side contact surface of the laser element. It may be, for example, a metallic layer whose chip-remote side consists for example of gold. Preference may be given to a galvanically reinforced gold layer having a thickness preferably greater than 0.5 pm, more preferably between 1 μιτι and 10 μητι, are used. Preferably, a metal can be selected whose electrical conductivity, which may be isotropic, is higher than the highest electrical conductivity of the heat spreader. It should be noted that the thermal conductivity of this metal, which may also be isotropic, may well be less than the highest thermal conductivity of the heat spreader. This metallic layer can be an advantageous

Lowering the electrical contact resistance between the heat sink and the laser bar cause. The combination of the heat spreader according to the invention with a metal layer on the contact surface of the laser bar can thus represent a particularly advantageous embodiment of the invention.

Namely, if only the gain ranges of the laser bar, i. H. the resonator structures or the wide strip areas are current-carrying, while in the spaces between individual

Emitters or the edge regions of the diode laser chip no current flows through the laser element, would without the above-mentioned thick metallization of the contact surface of the laser bar a

Set uneven current in the heat spreader. Without or with only a thin metal layer so the first contact surface would have an uneven distribution of the operating current. If now the current flow in the metal layer is spread in the layer plane, the power supply to the heat receiving surface of the heat spreader can be made over a large area. The physical effect can be explained as follows. Since the electrical conductivity of the heat spreader in the x-direction, even if in this direction the maximum electrical conductivity may be present, may be smaller than that of the metal of the metal layer, a thick metal layer with the o. preferred thickness can be considered as the equipotential surface of the electric field. Such a metal layer, which has the preferred thickness, can thus spread the operating current, i. H. a more uniform distribution of the operating current over the contact surface cause.

However, a metallic layer can also be on the n-side contact surface or on both

Be provided contact surfaces. This can lead, for example, in the x-direction the

 Current spreading takes place predominantly in the metal layer, while the heat spreading in the x-direction is mainly in the heat spreader. As a result, the current path and the heat path can have a different course. A metal layer, preferably of gold, can also the

Preventing oxide formation and reducing the electrical contact resistance across the interface. A gold layer can also be soft, so that only low mechanical stresses in the

Laser element occur.

The laser element can also be an optically pumped laser element. In this case, no power supply to the laser element is required.

The semiconductor laser comprises a first heat spreader, which may preferably be embodied as a solid (that is, as a compact or homogeneous) body. The first heat spreader is disposed between the laser element and the first heat sink. A solid body is understood to mean that it is not composed of individual layers or of particles that must be held together by forces, but rather that an intrinsic cohesion of the material

Material exists. This allows a mechanical processing, such. B. sawing or milling of the heat spreader be possible. One can define a solid heat spreader in an exact manner by having no internal interfaces lying between volumes of the same material. Such internal interfaces would be present, for example, in a laminated body or in a layer stack or in such a body, which has been formed by compressing particles, and could, for example, the strength or the affect thermal or electrical conductivity. The first heat spreader and also, if present, the further heat spreader may thus preferably consist of a homogeneous material which is anisotropic according to the invention.

The first heat spreader has a heat entrance surface in thermal contact with the first contact surface of the laser element. The heat input surface of the first

Heat spreader can rest directly on the first contact surface. The support surface is considered below as a heat input surface. It can also have the function of an electrical contact surface at the same time. Of course, the heat spreader can be larger than that

Can be formed contact surface of the laser element, so that only a part of the surface which limits the body on one side acts as a heat input surface. Although it would be possible to have several first

To use heat spreader, which are each thermally connected with its heat input surface with a partial surface of the first contact surface, the embodiment is preferred in which the contact surface of the laser element is connected to a single first heat spreader. The surface normal n of the heat input surface is defined below in such a way that it points into the interior of the heat spreader.

The first heat spreader has a heat exit surface in thermal contact with the heat sink. The heat input surface can be the same size as the heat exit surface. It can also be the largest of the surfaces that limit the heat spreader. The

Heat exit surface may preferably be parallel to the heat input surface. The first

Heat spreader may be cuboid.

Below is now the operation of the heat spreader in the context of

inventive design of the semiconductor laser described. The anisotropic thermal conductivity of the material of a heat spreader can be described by a second-order tensor q - = - 7λ ^■ - grad A ^ TT Equation ^a 1

Where λ is the thermal conductivity tensor of the material making up the heat spreader, q is the heat flow density vector, and gradT is the temperature gradient, which is also a vector.

 In the following, without limitation of generality, a Cartesian coordinate system is chosen as the reference system, in which the z direction of the normal n corresponds to the heat input surface of the heat spreader. The y-direction can be used in the case of a

edge emitting laser bars are chosen so that they the longitudinal direction of the Laser radiation in the resonator corresponds, that is in the direction of or the profit ranges. The direction y may be opposite to the direction of the exiting laser beam. The x-direction then results as normal to the yz-plane. You can, for example, the laser bar

Specify the direction of the offset of the emitter to each other and the direction of an edge of the

Light exit surface correspond. The heat input surface of the considered heat spreader is then in the xy plane.

In the prior art, for example, a graphite layer is arranged as Wärmeleitschicht in such a way that the direction Z ^'of the lowest thermal conductivity Ä _m in the z-direction, and the largest thermal conductivity Ä _M in the xz plane is present, wherein the thermal conductivity in be equal to x and y direction and may have a value λ _Μ . Then the thermal conductivity tensor may have the following shape:

This representation may be a symmetric tensor in diagonal form. Of the three main diagonal values λ _Μ , λ _Μ , λ _η , two may have the same amount λ _Μ , so that the

Thermal conductivity tensor has two different eigenvalues λ _Μ and Ä _m .

By contrast, according to the invention, based on the reference coordinate system xyz, there may be a transformation of the thermal conductivity tensor. For illustration, a

Thermal conductivity tensor X considered in a right-angled Cartesian

Coordinate stem x ^' y ^' z ^{'can take the} following form:

Since the mutually opposite directions z ^' and -z ^' are equivalent in terms of thermal conductivity, the sense of direction of z 'can be chosen without restriction of generality such that z ^' at the heat entrance surface points into the interior of the heat spreader. Therefore, the angle α defined below can be restricted to a value range of 0 ° to 90 °. The coordinate system x ^' y ^' z ^' should be linked via the transformation matrix M to the coordinate system xyz defined above, so that each vector r' in the coordinate system x ^' y ^' z ^'has the coordinates r in the coordinate system xyz

r = M - r '

 Then, the thermal conductivity tensor in the reference frame xyz according to the known

Transformation rule for a second-order tensor the following form: λ = Μ · Χ · Μ ^'χ

According to the invention, the coordinate system x ^' y ^' z ^{'may be} related to the coordinate system xyz, for example by a rotation about the x axis. The angle of rotation is the angle between n and z ^' , which comprises a value range of 0 ° to 90 °. The angle can

According to the invention have an amount between 5 ° and 90 ° or an amount of exactly 90 °. Then the matrix M has the following form:

In this case, the thermal conductivity tensor in the reference frame xyz then has the following shape

λ = 0 λ _Μ cos ² (or) + A _m sin ^{2 •} sin

0 A / ^~ A. sin (2or) Ä _m cos ² () + A _M sin ²

In order to illustrate this result, one can first consider a temperature gradient which is oriented in the z direction and has only one z component 71 different from 0:

 The z-direction is essentially the direction of the intended heat flux from the laser element to the heat sink, i. h, the direction from the heat entrance surface to the heat exit surface of the heat spreader. It should be noted that this consideration is only for the understanding of the invention. In practice, temperature gradients also occur in the xy plane.

In this simplified view, the heat flow q according to Equation 1 has the following form: Equation 2

 This shows that the direction of the heat flow can deviate from the direction of the temperature gradient if the angle a is neither 0 ° nor 90 °. When using graphite foils according to the prior art, the rotation angle a = 0. Therefore, the amount of

Heat flux density q = T _z A _m . Thus, as is known, only the minimum thermal conductivity A _m is available for the passage of the heat from the heat entry surface to the heat exit surface. According to the invention, an angle a can preferably be selected between 5 ° and 90 °. If the material of the heat spreader is a strongly anisotropic material with A _M »A _m , then, under this approximation from equation 2, an amount of the heat flow density q = TA _M - sin (ar) is obtained.

This means that with the solution according to the invention in comparison to the prior art, a larger amount of heat can be dissipated by the laser element. Advantageously, the angle a should be chosen from this observation so that A _M -sin (ar) is greater than A _m . For example, if A _M : A _m e ^' m ratio is 100: 1, and a is only 5 °, A _M - sin (ör) is nine times higher than A _m . This shows that the measure according to the invention has a great positive effect on the heat transmission through the heat spreader even at small angles a. Likewise, the electrical power supply may also be improved, as described below.

However, the angle of rotation a is not limited to small angles, it may also preferably be a right angle or be selected close to 90 °. The direction z 'of the lowest thermal conductivity may, for example, lie in the direction y (longitudinal direction of the laser radiation in the laser element). Then the heat transfer through the heat spreader in the z-direction by utilizing the maximum thermal conductivity t _{M of} the material is possible. However, then the heat spreading in the heat spreader is mainly possible only in the x-direction, while in the y-direction, the low thermal conductivity A _m acts, causing the heat spreading in y-direction can occur only to a very small extent.

Such an effect can be used to design the temperature profile of the laser element. For example, it may be advantageous to choose the angle a as the right angle and the direction z ^'of the lowest thermal conductivity in the x-direction, ie perpendicular to the longitudinal direction of the To lay laser radiation. As a result, it is possible to suppress heat spreading in the x-direction as far as possible in order, for example, to achieve heat dissipation which is the same for every emitter of a laser bar. This may be advantageous, for example, to minimize the known phenomenon that the middle emitters are more heated in the operation of the laser bar relative to the edge emitters. Another advantageous effect of this measure can be that the temperature distribution in the x-direction over the width of an emitter is more homogeneous than with existing heat spread. An emitter of a laser bar is known as a result of

Heat spreading in the middle warmer than at the edges of the emitter. According to the invention, it is now possible to minimize the heat spreading in the x-direction in the manner described above. This makes it possible to homogenize the temperature profile in the emitter and thus the negative

To reduce effects of the formation of a thermal lens in the resonator.

If the low heat spreading in one direction is undesirable however, than

Countermeasure, the introduction of a third and fourth described below

Heat spreader be provided, or the angle a is less than 90 °, preferably less than 85 ° selected.

However, it may also be that a heat spread in one direction, for example x, is desired, not required in another direction, for example in the y direction, because, for example, the heat input on the heat entrance surface in the y direction is homogeneous. Then it may be advantageous to choose the angle a as the right angle and the direction z ^'of the lowest

Thermal conductivity in the y direction to lay. Then you can use the best possible heat transmission in the z direction and the best possible heat spread in the x direction combined. In a further preferred embodiment, a rotation angle a deviating from the right angle may be provided, for example an angle of 45 ° about the x-axis. In this case, more than 70% of the maximum thermal conductivity λ _{Μ of} the material can be used both for the passage of heat from the heat inlet surface to the heat outlet surface of the heat spreader, while also more than 70% of λ _{Μ are available} for heat spreading in the heat spreader in the y direction. In the x-direction would then even the maximum thermal conductivity for

Heat spread are available.

Of course, the rotation can also take place about another axis, for example the y-axis. Furthermore, a different axis of rotation in the xy plane can be selected, which may for example have an angle of 45 ° to the x-axis. The basic idea of the invention is thus the use of a first anisotropic heat spreader having a heat entrance surface whose normal n points in a direction z, wherein the minimum of the directional thermal conductivity of the heat spreader lies in a direction z ^' . The direction z according to the invention has an angle a of 5 ° to 90 ° to the direction z ^' .

The electrical conductivity of the first heat spreader may also be anisotropic. The electrical conductivity of the heat spreader can also be represented as a tensor second stage.

-: ⁼ ~ Equation 3

] = σ · Ε ^a

Where σ is the electrical conductivity tensor of the material making up the heat spreader, j is the vector of current density, and E is the electric field strength, which is also a vector.

 The electrical conductivity tensor can have the following shape analogous to the thermal conductivity tensor:

 0 0

σ = 0 0

 0

Of the three main diagonal values (eigenvalues) σ _Μ , σ _Μ , σ _ηι , two can have the same maximum amount σ _Μ , so that the electrical conductivity tensor has two different eigenvalues, namely the maximum thermal conductivity σ _Μ and the minimum (lowest)

Has thermal conductivities.

The direction of minimum electrical conductivity may coincide with the direction z ^' of minimum thermal conductivity. The coordinate system of the principal axes of this tensor can therefore be oriented in the same way as in the tensor of the thermal conductivity. Since the electrical and thermal conductivity of solids are often directly related, the electrical conductivity can also have a similar ratio between the minimum value and the maximum value. The minimum electrical conductivity may be in the same direction z ^' as the minimum of the thermal conductivity. Therefore, the above-mentioned inventive introduction of a rotation angle a equally leads to a significant improvement of the power supply to the laser bar. If, as in the above example calculations, the heat connection by factors 9 or Can be improved, the resulting in the interior of the heat spreader electrical power loss can be reduced by such a factor.

The heat spreader according to the invention can be embodied as a homogeneous anisotropic body. This means that it does not consist of individual slats, for example, but consists of a solid piece of material. As a material for heat spreader is oriented or highly oriented TPG (thermal pyrolytic graphite) into consideration. With known

Manufacturing processes can be produced plane-parallel flat blanks, which are expanded in a plane xy and in the z-direction has a thickness d. The ab-levels are the

Grafitbestandteile the TPG aligned substantially perpendicular to z. The greater the thickness d, the higher the random angular errors of this orientation in the material can be. Random angle errors can significantly reduce the thermal conductivity of the material. Around

To produce heat spreader according to the invention, TPG material of greater thickness is required. For this purpose, special manufacturing processes that produce small angle errors are suitable. WO 2005/029931, for example, a method for the production of TPG with low

Angular error known. This TPG can be made in large thickness, from which the

Heat spreader according to the invention can be manufactured. The material TPG is a three-dimensionally ordered graphite structure with a high thermal conductivity in the xy plane, which corresponds to the preferred orientation of the ab plane of the graphite. The thermal conductivity may be greater than 1000W / (m * K) or preferably greater than 1500 W / (m * K). The thermal conductivity in the z ^' direction, which corresponds to the preferred orientation of the graphite in the c direction, may be less than 20 W / (m * K). The surface of the first heat spreader or the other

Heat spreader may, but need not, be provided with a metal layer. A metal layer may, for example, on the heat input surface and / or the heat exit surface of the

Heat expander be attached. The metal layer may for example consist of copper. In addition, it may additionally have a gold surface and a diffusion barrier, for example of nickel, so that the layer sequence may have the following structure: Cu-Ni-Au. Between the

Base material and the Cu layer may be an adhesion-promoting layer, so that delamination is prevented. The gold surface can be soldered and used to attach the

Laser element may be provided on the heat input surface by soldering. The heat exit surface may, for example, have said metallization in order to connect the heat exit surface of the heat spreader to the heat sink by soldering. Metallization of the surface can also improve the stability and mechanical workability of the surface

Improve heat spreader. The semiconductor laser may further comprise a lid. The lid can have the function of a heat sink (second heat sink) or without thermal function. By way of example, the cover can be connected in a planar manner to the first heat sink via a joining surface by means of a heat-conducting joining agent layer, for example an electrically insulating heat-conducting adhesive, so that the heat can be dissipated from the cover to the first heat sink.

The cover can serve for power supply, for example as n-side contact terminal. With the help of the lid, a clamping force can be exerted on the laser element. This can be used for the frictional connection between the first contact surface and the heat input surface of the first heat spreader and / or for non-positive connection of the heat exit surface of the first heat spreader and the heat receiving surface of the heat sink or the

Heat input surface of the third heat spreader lead. In the same way, the clamping force can effect a frictional connection of the second contact surface to the heat input surface of the second heat spreader. Thus, the laser element can frictionally with the first

Heat spreader and / or be connected to the second heat spreader. Such a frictional connection can be advantageous for various reasons. Then namely can be dispensed with an example solderable coating of the heat spreader. In addition, the semiconductor laser can be disposed of more easily because the components are easier to separate than a solder joint. The clamping force can be applied for example by a spring element, which may be formed for example as a spring washer or as a compression spring. The use of a spring element is advantageous if the first heat spreader is plastically deformable or rigid. If the first heat spreader, however, is elastic, the clamping force can also be applied by itself. Then, the lid can be mechanically rigidly connected to the first heat sink, for example, without spring element. This connection can be made electrically insulating, so that the cover and the first heat sink to electrical

 Contacting the laser element can be used. For this purpose, an insulating element, for example an insulating disk or an insulating bush can be used.

The first angle a may preferably be between 10 ° and 90 °. Also preferably, it may be a right angle.

The thermal conductivity of the first heat spreader can have in each direction, which lies in a plane xy ^' perpendicular to the direction z ^{' of} the lowest thermal conductivity of the heat spreader, an approximately equal value, which is the maximum value of the direction-dependent

Thermal conductivity is. The semiconductor laser may additionally comprise at least one second laser element designed as a laser bar, which is arranged offset to the first laser element. The second laser element can be electrically connected in parallel to the first laser element. In this case, a common first heat spreader can be provided for both laser elements. Alternatively, the second laser element may be connected in series with the first laser element. For this purpose, a separate associated first heat spreader may be present for each laser element.

Furthermore, the semiconductor laser, a second heat spreader with anisotropic

Thermal conductivity and a second heat sink, wherein the laser element has a second contact surface which is in thermal contact with a heat input surface of the second heat spreader and the second heat spreader further comprises a heat exit surface, which is in thermal contact with a heat receiving surface of the second heat sink. Also in the second heat spreader, the heat exit surface parallel to

Be heat input surface.

The maximum electrical conductivity of the heat spreader may be smaller than the electrical conductivity of a metal, which may be applied, for example, as a layer on the first contact surface of the laser element. For example, the maximum electrical conductivity of a TPG body can be 10 ⁵ to 10 ⁷ (ohm * m) ^-1 , while a gold layer can be an (isotropic) electrical

May have conductivity of 4.5 * 10 ^'7. The maximum electrical conductivity of the Wärmespreizkörpers can thus for example 5 to 20 may be times lower than that of the metal layer, while a maximum thermal conductivity from 3 to 6 may be times higher than that of the metal layer. The

Thermal conductivity of a gold layer may be, for example, 300 W (m * K), while the maximum thermal conductivity of a TPG body may be 1000 to 2000 W / (m * K). Therefore, the metal layer may be mainly provided for current spreading, while the

Heat spreader, however, can be mainly provided for heat spreading. By combining the heat spreader with a metal layer, which may be applied to the first contact surface of the laser element, therefore, a particularly advantageous embodiment of the invention can be produced. For the sake of completeness, it should be noted that the lowest electrical conductivity cr _{m of} the TPG heat spreader can even be smaller by a few orders of magnitude than its maximum electrical conductivity σ _Μ . For example, a _{m may have} an amount of only 10 ³ to 10 ⁵ (ohm * m) ^-1 . The thermal contact between the heat exit surface of the first heat spreader and the first heat sink can by means of a third heat spreader with anisotropic

Thermal conductivity can be effected by the heat exit surface of the first

Heat spreader in thermal contact with a heat input surface of the third

Heat spreader is and a heat exit surface of the third heat spreader is in thermal contact with the heat receiving surface of the first heat sink. In this case, the direction of the lowest thermal conductivity of the third heat spreader perpendicular to

Surface normal of the heat input surface of the third heat spreader be oriented. The

Also, the direction of least heat conductivity of the third heat spreader may be different from the direction of least heat conductivity of the first heat spreader. In the same way, the thermal contact between the heat outlet surface of the second heat spreader and the second heat sink can be effected by means of a fourth heat spreader having anisotropic thermal conductivity in that the heat exit surface of the second heat spreader in thermal contact with a heat input surface of the fourth

Heat spreader is and a heat exit surface of the fourth heat spreader is in thermal contact with the heat receiving surface of the second heat sink. In this case, the direction of the lowest thermal conductivity of the fourth heat spreader perpendicular to

Surface normal of the heat input surface of the fourth heat spreader be oriented. In addition, the direction of least heat conductivity of the fourth heat spreader may be different from the direction of least heat conductivity of the second heat spreader.

The first heat spreader may comprise or consist of graphite, for example pyrolytic graphite. Particularly preferably, the heat spreader comprises or consists of highly oriented pyrolytic graphite.

The first heat spreader may have a thickness of 0, 1 mm to 10 mm, preferably 0.2 mm to 5 mm.

The laser element may be non-positively connected to the first heat spreader and / or the second heat spreader.

The first heat spreader may be subjected to pressure treatment prior to assembling the semiconductor laser of the present invention. As a result, a later, for example, deformation of the heat spreader during assembly of the semiconductor laser can be prevented or greatly reduced. In addition, settlement phenomena of the heat spreader in the finished assembled semiconductor laser can be avoided or limited. As a result, the semiconductor laser will have good long-term stability, in particular with regard to the position of the emitter. Another advantage of the pressure treatment is that the flatness of the surfaces, i. h the heat input surface and the heat outlet surface can be improved. This means that the roughness of said surfaces can be reduced.

The pressure treatment can be carried out by subjecting the heat spreader to a uniaxial pressure perpendicular to the heat input surface. The pressure can be effected for example by a press with, for example, two flat surfaces, wherein a force in the normal direction is applied to the heat input surface. For example, the pressure can be maintained for a few seconds to several days. The pressure can be either constant or pulsating. Under this pressure treatment, the thickness of the heat spreader can decrease. The pressure may preferably be higher than that occurring later in use in the semiconductor laser according to the invention, preferably at least three times as high. The pressure treatment can lead to a compression of the material. By the pressure treatment, the deformability (compressibility) of the heat spreader can decrease or increase its hardness. In addition, the pressure treatment can lead to an increase in electrical conductivity. The pressure treatment can be combined with a heat treatment. Likewise, the second, third and / or fourth heat spreader can also be treated. Said pressure treatment is not only suitable for the heat spreader. Also, a conventional carbon foil with an angle a = 0 ° can be subjected to such a pressure treatment. In the pressure treatment, in addition to the above-described force in the normal direction at the same time a thrust component in

Tangentialrichtung be applied to the heat input surface. As a result, the ab planes of the graphite can be influenced, so that in addition to the aforementioned positive effects, a better electrical conductivity for passing the electric current through the

Heat spreader can be achieved.

The pressure treatment can also be done before the preparation of the geometric shape of the

Heat expansion carried out.

The pressure treatment can also be done by rolling the material between two rolls. The rolling technology may be particularly suitable for thin materials, for example, preferably thinner than 1 mm thickness, for example, carbon film with a thickness of 25 pm to 500 μιτι. From a plurality of semiconductor lasers according to the invention, an arrangement can be set up in which at least two of the laser elements are electrically connected in series. These are the

Heat spreader of the at least two semiconductor lasers against each other to electrically isolate. Further important features of the present invention will become apparent from the following detailed description in conjunction with the claims and figures. Hereinafter, preferred embodiments of a device according to the invention are described and explained in more detail by means of the figures.

 Fig. 1 shows a fourth embodiment with a = 45 °

Fig. 2 shows a first embodiment with existing heat spreading in the x direction in

sideview

 Fig. 3 shows the first embodiment in front view

 Fig. 4 shows the effect of the metal layer on the electric current density at the first

embodiment

Fig. 5 shows a detail A in a detailed representation

 Fig. 6 shows a second embodiment with suppressed heat spreading in the x direction in front view

 Fig. 7 shows a third embodiment with a third heat spreader

 Fig. 8 shows a fifth embodiment with a second heat spreader

Fig. 9 shows the fifth embodiment in exploded view

 10 shows a sixth exemplary embodiment in which a plurality of laser bars, each having an emitter, are electrically connected in parallel

A first exemplary embodiment of a semiconductor laser according to the invention is shown in FIGS. 2, 3 and 4. To illustrate the essential features, the figures are not drawn to scale.

The semiconductor laser comprises a laser element 1, which, as shown in FIG. 2, emits laser radiation 1 2 in a direction defined as -y. The laser element is a diode laser bar with multiple emitters, for example with 19 emitters. In FIG. 3, for the sake of clarity, only three emitters are shown, which each have a gain region 13, which corresponds in the illustrated view to the exit aperture. The exit aperture is at the bottom of the chip

shown side, which is the epitaxial side of the laser bar. The first contact surface is thus the p-contact (anode) of the diode laser bar. The laser element has on the first contact surface on a gold layer 9 with a thickness greater than 0.5 μιη for spreading or distribution of the electrical operating current. The thickness of the gold layer can be for example 4μιη and be prepared by electroplating. The surface normal n of the first contact surface is oriented in the z-direction.

The semiconductor laser of the first embodiment further includes a first heat sink 17 and a second heat sink 22. The semiconductor laser of the first embodiment further includes a first one

Heat spreader 14 of highly oriented pyrolytic graphite on. This material has an anisotropic thermal conductivity that has a direction z ^' of least heat conductivity. The thickness of the first heat spreader is 0.5 mm. The direction z ^'of the least

Thermal conductivity of the first heat spreader is at a first angle of 90 ° to

Surface normal n the heat input surface of the first heat spreader oriented. The direction z 'points in the direction -y (see FIG. 2). The direction of least thermal conductivity of the first

Heat spreader is thus in the longitudinal direction of the laser radiation in the laser bar (y direction). This y-direction is also the main propagation direction of the emergent laser beams 12.

The first contact surface 2 is in thermal contact with a heat input surface 1 of the first heat spreader 14. The thermal contact is effected by the gold-plated first contact surface rests on the heat input surface and by a clamping force 26 surface

is pressed. The heat input surface of the first heat spreader has a first

Surface normal n, which is oriented in the z direction. The laser element is thus non-positively connected to the first heat spreader. The first heat spreader also has a

Heat exit surface 16, which is in thermal contact with a heat receiving surface 18 of the first heat sink 17. This thermal contact is effected in the same way by the clamping force 26.

The clamping force 26 is effected by a cover 22 which is fastened with screws 27. The screws are equipped with spring elements 28 and mounted electrically insulated from the cover by means of insulating washers 29. The lid is provided here without thermal function. But it could also be used as a second heat sink, if you installed a heat dissipation from the lid, for example, by water cooling, or if the lid thermally with the first Heat sink is connected. The cover is made of copper and serves to supply power, so as n-side (substrate side) contact terminal for the laser bar, while the p-side electrical connection is made via the first heat sink. The operating voltage is thus applied between the first heat sink 17 and the cover 22. The operating current must therefore flow with a z-component over the first heat spreader 14.

With the first embodiment, a method for heat dissipation from the laser element is practiced, in which a heat spreading takes place in the x direction, as shown in Fig. 3. There, for example, three vectors of the heat flux q are shown for an emitter 13, which represent the direction of the heat flow by way of example. Because of the orientation 25 of the anisotropic material of the heat spreader 14, the heat spread in the y direction is negligibly small.

The heat transfer through the heat spreader 14 takes place in the z-direction, i. the vectors q have a z-component, while the y-component is vanishingly small, as can be seen in FIG. The heat spreading takes place mainly in the heat spreader 14 and only a small part in the metal layer 9, since the maximum value of the thermal conductivity of the

 Heat spreader, i. in y 'direction, is higher than the thermal conductivity of the metal layer. 9

4, the current flow j of the first embodiment is shown schematically. Of the

For clarity, only the laser element 1 and the first heat spreader 14 are shown in the figure, while the heat sink, the lid and the screws are not shown. To illustrate the distribution of the operating current vividly, is for the flow of current through the first

Wärmeleitkörper the opposite direction of current -j drawn. There is a

 Current spreading in the metal layer 9, which is due to the fact that the electrical conductivity of the metal layer is higher than the maximum value of the electrical conductivity of the

Heat spreader, i. in y 'direction. As a result, the current path differs from the heat path described above according to FIG. 3. The spreading or distribution of the operating current in the metal layer 9 thus causes the current flow in the z direction to be determined by the first

Heat spreader 14 has a higher cross-sectional area is available. As a result, the ohmic resistance and thus the power loss of the semiconductor laser can be reduced. From this consideration, the advantage of combining the heat spreader 14 according to the invention with a thick metallization layer 9 on the laser element becomes clear.

This situation is illustrated in more detail in FIG. 5, which shows the detail A of FIG. 4 enlarged. The laser bar 1 comprises a substrate 3, a light guiding layer 4, an active one Layer 5, a further light guide layer 4, a cover layer 6, a structured insulation layer 7, an electrode 8 (anode, p-side) and a gold layer 9. On the cover layer 6, the structured insulating layer 7 is applied, which is interrupted in the central region of the illustration is. The region in which the insulation layer is interrupted has a constant width (extension in the x-direction) (which is independent of the y-coordinate), thereby defining a corresponding emitter strip of the laser bar. The emitter width is Ι ΟΟμιτι on this structured

Insulation layer is the electrode 8, which was prepared by sputtering and has a thickness of less than 0.5 μπι. This electrode was galvanically strengthened, so that a

Gold layer 9 of 4 pm thickness has emerged. The operating current is supplied from below via the first heat spreader 14. The current flow is shown schematically by the arrows 10.

Due to the insulating layer, only certain regions of the active layer are electrically pumped so that the formation of the laser radiation is limited locally to fixed gain regions 13. Since the current is spread laterally (x-direction) in the metal layer 9, it can be cut in the shortest path, i. H. in the z-direction over the entire surface are passed through the heat spreader 14.

A second embodiment of a semiconductor laser according to the invention is shown in FIG. In contrast to the first embodiment, the direction z 'of the lowest thermal conductivity of the first heat spreader 14 is oriented perpendicular to the direction y profit areas. The direction z 'here points in the direction x, the ab planes 25 of the graphite material lie parallel to the yz plane. Therefore, no significant heat spreading occurs in the heat spreader in the x direction. The heat transfer through the heat spreader takes place in the z-direction. This is one of the two directions with maximum thermal conductivity. The other direction x 'maximum thermal conductivity of the

Heat spreader is oriented in the direction of y. Therefore, a heat spreading in the y-direction can take place. This embodiment is to be preferred if a homogeneous temperature distribution over the profit ranges is desired. Since the heat flow in the x-direction is minimal, it is avoided that the profit regions (emitters) are better cooled at the edges, respectively, than in the middle of the respective profit region. Thereby, the formation of thermal lenses in the resonators can be avoided. A current spread in the metal layer 9 provided for this takes place in the same way as in the first embodiment.

A third embodiment of a semiconductor laser according to the invention is shown in FIG. In contrast to the first embodiment, the thermal contact between the

Heat exit surface of the first heat spreader and the first heat sink not directly, but by means of a third heat spreader 24 causes anisotropic thermal conductivity, which also consists of pyrolytic graphite. The heat outlet surface of the first heat spreader is lying flat on a heat input surface of the third heat spreader. This is the heat output surface of the first

Heat spreader in thermal contact with this heat input surface of the third

Wärmespreizkörpers. A heat exit surface of the third heat spreader is flat on a heat receiving surface of the first heat sink. Thereby, this heat exit surface of the third heat spreader is in thermal contact with the heat receiving surface of the first heat sink.

The direction z 'of the lowest heat conductivity of the third heat spreader is oriented perpendicular to the surface normal of the heat entrance surface of the third heat spreader, and the direction z' of the lowest heat conductivity of the third heat spreader 24 is different from the direction of least heat conductivity z 'of the first heat spreader 14. In this

Embodiment, the direction z 'of the first heat spreader is oriented in the direction -y, while the direction z' of the third heat spreader is oriented in the direction x.

In the same way, in a further non-figuratively illustrated embodiment, the thermal contact between the heat outlet surface of the second heat spreader and the second heat sink can be effected by means of a fourth heat spreader with anisotropic thermal conductivity, characterized in that the heat exit surface of the second heat spreader in thermal contact with a heat input surface of the fourth heat spreader stands. A heat exit surface of the fourth heat spreader is in thermal contact with the

Heat receiving surface of the second heat sink and the direction of least heat conductivity of the fourth heat spreader is oriented perpendicular to the surface normal of the heat input surface of the fourth heat spreader. The direction of least heat conductivity of the fourth heat spreader is different from the direction of least heat conductivity of the second heat spreader. In this embodiment, the direction z 'of the second

Heat expansion body in the direction -y oriented, while the direction z 'of the fourth

Heat spreader is oriented in the direction x. A fourth embodiment is shown in FIG. Here the angle a = 45 ° is selected. The

Direction z ^'of the lowest thermal conductivity of the first heat spreader 14 thus includes a first angle «on 45 ° to the surface normal n of the heat input surface 1 5 of the first

Heat spreader. The coordinate system x'y'z 'is 45 ° opposite to the

Coordinate system xyz rotated about the x-axis. Although the electric field -E is oriented in the z direction, the electric current density j in the heat spreader is adjacent to the z component also a y component. The current flow j is therefore not parallel to the field strength vector E. The plotted vector - j (opposite current direction) is as shown

Fig. 1 directed to the bottom right. The heat flow q also has a z next to the component

Component in the direction of y and therefore flows in the illustration also to the bottom right. This is advantageous because the heat sink 1 7 and the heat spreader 14 should not project beyond the facet of the laser bar 1 in the beam direction 12, but may project beyond the length of the laser bar in the direction y. As a result, the heat from the laser bar equal to the beam direction 12 are partially derived backwards. A fifth embodiment is shown in FIG. Here, the lid 22 is designed as a second heat sink. The heat dissipation from the laser bar occurs on the epitaxial side with a first

Heat spreader 14 and a first heat sink 17, while the substrate side, a second

Heat spreader 19 and a second heat sink 22 are provided. Both heat spreader 14, 19 are designed in the manner according to the invention so that in each case a direction Z ^'of the lowest thermal conductivity of the first and the second heat spreader each an angle «of more than 45 ° to the surface normal n of the heat input surface of the first heat spreader or to the surface normal n _{2 of} the second heat spreader includes. In an analogous manner, a heat flow q ₂ then flows from the laser element 1 through the second heat spreader to the second heat sink (cover) 22.

Both heat sinks 17, 22 are made of copper. The second heat sink 22 is connected by means of an electrically insulating Wärmeleitklebers 30 as a joining means with the first heat sink 17 surface. Therefore, the heat can be transferred from the second heat sink to the first heat sink. In addition, the clamping force 26 between both heat sinks is maintained by the joining means 30 without requiring any external force for the operation of the semiconductor laser.

Fig. 9 shows an exploded view of the fifth embodiment. Here are the first

Contact surface 2, the thick gold layer 9 located thereon and the second contact surface 1 1 of the laser element 1 can be seen. The surface 15 is the heat input surface, the surface 9 the

Heat exit surface 16 of the first heat spreader 14. The surface 18 is the

Heat receiving surface of the first heat sink 17. The surface 20 is the heat input surface, the surface 21, the heat exit surface of the second heat spreader 19. The surface 23 is the Heat receiving surface of the second heat sink 22. The area designations apply equally to all embodiments.

In a modification of the fourth exemplary embodiment, which is not shown in a figurative form, no second heat spreader is provided, but the second contact surface of the laser element is directly adjacent to the heat receiving surface of the second heat sink. The step height of the heat sinks is then of course run correspondingly lower.

10 shows a sixth exemplary embodiment in which a plurality of laser bars 1, each having an emitter 13, are electrically connected in parallel. The first heat spreader 14 is correspondingly wide (expanded in the x direction), so that a plurality of laser elements 1 can each be arranged offset in the direction x relative to one another. Each laser bar 1 has only one emitting area (wide-band emitter) 13. Such laser bars are also referred to as a single emitter. They are electrically contacted together via the first heat sink 17 and the cover 22.

Reference numerals:

 1 . laser element

 2. first contact surface, for example p contact

 3. Substrate

 4. Light guiding layer (cladding)

 5. active layer (quantum well structure)

 6. Topcoat

 7. Insulation layer

 8. electrode (p-contact)

 9. metal layer

 10. Operating current

 1 1. second contact surface, for example n contact

 12. exit direction of the laser radiation

 13th profit range, emitter

 14. first heat spreader

 1 5. heat input surface of the first heat spreader

16 heat exit surface of the first heat spreader

17th first heat sink

 18. heat receiving surface of the first heat sink

 19. second heat spreader

 20. heat input surface of the second heat spreader

21. Heat exit surface of the second heat spreader

22. Lid, second heat sink

 23. heat receiving surface of the second heat sink

 24. third heat spreader

 25. ab planes, for example, a hexagonal graphite structure

26. Clamping force

 27. Fasteners, screw

 28. spring element

 29. insulation element

 30. Joining agent

Claims

claims: 1 . A semiconductor laser comprising a laser element (1), a first heat spreader (14) with anisotropic thermal conductivity, which has a lowest thermal conductivity in a direction z ^' , and a first heat sink (17), the laser element having a first contact surface (2) is in thermal contact with a heat input surface (1 5) of the first heat spreader (14) and the heat input surface of the first heat spreader has a first surface normal n and the first heat spreader (14) further comprises a heat exit surface (16) in thermal contact with a  Heat receiving surface (18) of the first heat sink (17) is,  characterized, that the direction z ^'of the lowest thermal conductivity of the first heat spreader (14) includes a first angle or of more than 5 ° to the surface normal n of the heat entrance surface (15) of the first heat spreader (14). 2. A semiconductor laser according to claim 1, characterized in that the first angle is between 10 ° and 90 ° or the first angle or a right angle. 3. A semiconductor laser according to one of the preceding claims, characterized in that the laser element (1) is a diode laser bar with one or more emitters. 4. The semiconductor laser of claim 3 further comprising at least a second laser bar configured as a laser element, which is arranged offset to the laser element and is electrically connected in parallel to the laser element. 5. A semiconductor laser according to one of the preceding claims, further comprising a second heat spreader (19) with anisotropic thermal conductivity and a second heat sink (22), wherein the laser element has a second contact surface (1 1), in thermal contact with a heat input surface (20). of the second heat spreader and the second heat spreader further comprises a heat exit surface (21) in thermal contact with a heat receiving surface (23) of the second heat sink. 6. A semiconductor laser according to one of the preceding claims, characterized in that the laser element (1) has one or more electrically pumped gain ranges and that the laser element on the first contact surface (2) has a metal layer (9) with a thickness greater than 0.5 pm Spreading the electrical operating current has. 7. A semiconductor laser according to one of the preceding claims, characterized in that the thermal contact between the heat exit surface (16) of the first heat spreader (14) and the first heat sink (17) by means of a third heat spreader (24) is effected with anisotropic thermal conductivity that the heat exit surface (16) of the first heat spreader is in thermal contact with a heat entrance surface of the third heat spreader and a heat exit surface of the third  Heat spreader is in thermal contact with the heat receiving surface (18) of the first heat sink and the direction of least thermal conductivity of the third  Heat spreader is oriented perpendicular to the surface normal of the heat input surface of the third heat spreader and the direction of least thermal conductivity of the third heat spreader is different from the direction of least thermal conductivity of the first heat spreader  and or  that the thermal contact between the heat exit surface of the second  Heat spreader (19) and the second heat sink (22) by means of a fourth  Heat spreader having anisotropic thermal conductivity is effected in that the heat exit surface of the second heat spreader is in thermal contact with a heat input surface of the fourth heat spreader and a heat exit surface of the fourth heat spreader is in thermal contact with the heat receiving surface of the second heat sink and the direction of least heat conductivity of the fourth heat spreader vertically is oriented to the surface normal of the heat input surface of the fourth heat spreader and the direction of least thermal conductivity of the fourth heat spreader is different from the direction of least heat conductivity of the second heat spreader 8. A semiconductor laser according to one of the preceding claims, characterized in that the first heat spreader (14) comprises graphite, preferably oriented pyrolytic graphite or consists of this. 9. A semiconductor laser according to one of the preceding claims, characterized in that the first heat spreader (14) has a thickness of 0.2 mm to 5 mm. 10. A semiconductor laser according to one of the preceding claims, characterized in that the laser element (1) is non-positively connected to the first heat spreader (14) and / or the second heat spreader (19). 1 1. Semiconductor laser according to one of the preceding claims, characterized in that the laser radiation in the laser element has a longitudinal direction y, which is parallel to the first contact surface, and the direction z 'of the lowest thermal conductivity of the first  Heat spreader (14) lies in the direction of the longitudinal direction. 12. A semiconductor laser according to claim 1 to 10, characterized in that the laser radiation in the laser element has a longitudinal direction y, which is parallel to the first contact surface, and the direction z 'of the lowest thermal conductivity of the first heat spreader (14) perpendicular to the direction of the longitudinal direction lies. 13. A method for heat dissipation of a laser element by means of a heat spreader (14) with anisotropic thermal conductivity according to one of the preceding claims, which has a heat input surface (15) with a surface normal n, characterized in that the direction of least heat conductivity of the heat spreader (14) in an angle of more than 5 ° to the surface normal n is arranged. 14. A method for reducing or eliminating the compressibility of pyrolytic graphite with anisotropic thermal conductivity for use as a heat spreader (14) according to one of the preceding claims, comprising the following steps:  Preparation of pyrolytic graphite with two parallel surfaces,  Applying a uniaxial static or dynamic pressure from one to the other Surface of the pyrolytic graphite,  Removal of uniaxial pressure,  Production of the heat spreader with a heat input surface of the pyrolytic graphite,  wherein the maximum of the uniaxial static or dynamic pressure exceeds by a force fit on the heat input surface pressure force in a built-in state of the heat spreader into a semiconductor laser according to one of claims 1 to 12 at least three times. A method according to claim 14, characterized in that during the step of  Applying a pressure, a heat treatment takes place.