Laser diode device

Abstract

laser diode device comprising a housing (1) with a housing part (10) and with a mounting part (11) connected to the housing part (10), which extends away from the housing part (10) along a direction of extension (110), and a laser diode chip (2) on the mounting part (11) which has semiconductor layers (21, 22, 23, 24, 26) with an active layer (23) for emitting light on a substrate (20), where the housing part (10) and the mounting part (11) have a base body made of copper and at least the housing part (10) is steel-clad, a first solder layer (3) is arranged between the laser diode chip (2) and the mounting part (11), which has a thickness of greater than or equal to 3 µm, the laser diode chip (2) is based on a nitride compound semiconductor material and has a non-polar or semi-polar crystal structure, and the first solder layer (3) has a soft solder based on indium.

Description

[0001] A laser diode device is specified.

[0002] Light sources with high optical power density are key components for a wide variety of applications. For example, laser diodes made from a nitride-based compound semiconductor material system have high market potential for projection systems, especially those with luminous fluxes between 1000 and 10000 lumens.

[0003] For such applications, components with high output power and compact packages are therefore necessary. For cost reasons and within the framework of standardization, packages of the so-called TO series (TO: "transistor outline") in the form of TO metal packages ("TO metal can") are common, for example in the familiar sizes TO38, TO56, and TO90, with the TO metal packages being made primarily of steel. However, currently available laser diodes in such standard TO packages, hereinafter also referred to simply as "TO packages," are limited to optical powers below 3 watts, which is insufficient for many applications. To date, it has not yet been possible to achieve optical powers above 3 watts with such packages.

[0004] For example, blue emitting nitride-based laser diodes in TO packages are known from the publication C. Vierheilig et al., Proc. SPIE, Vol. 8277, 82770K, 2012, which can emit light with a wavelength in the range of 440 nm to 460 nm at room temperature in continuous wave operation with a maximum output power of 2.5 watts.

[0005] An increase in optical output power is usually attempted by increasing the dimensions of the optical resonator, and in particular the chip area, since nitride-based laser diodes have been shown to exhibit current density-dependent long-term aging behavior, as described, for example, in the publication by S. Lutgen et al., Proc. SPIE, Vol. 7953, p. 79530G, 2011. Furthermore, increasing the active area can also improve heat transfer from the light-generating layer towards a heat sink.

[0006] However, the inventors of the present application have found in their own investigations and studies that increasing the chip area does not lead to an increase in performance. In this regard, Fig. Figure 1A shows measurements of the optical output power P (in watts) as a function of the operating current I (in amperes) for blue-emitting laser diode chips based on a nitride compound semiconductor material. The laser diode chips used for the measurements were each housed in a TO package. For two individual chips, each with a component size of 200 µm × 1200 µm and an active area of ​​15 µm × 1200 µm, the measurement curves 1001 and 1002 were determined. To achieve higher power levels, the approach described above of doubling the chip area was investigated. The expected power increase from such a doubling is indicated by the dashed line 1003.However, it has been shown that the achievable maximum power with double the chip area is, contrary to expectations, even lower than in the case of individual chips, as can be seen from curve 1004 for a laser diode chip with twice the active area compared to the previously described individual chips.

[0007] To increase the efficiency of light generation in laser diode chips, for example by reducing injection barriers for electrons and holes during current flow into the light-generating quantum films, laser diode chips grown on nonpolar or semipolar substrates are also known, as described, for example, in the publication by U. Strauss et al., physica status solidi, Vol. 248, pp. 652-657, 2010. However, as described in the publication by D. Sizov et al., IEEE Journal of Lightwave Technology, Vol. 30, pp. 679-699, 2012, the achievable electrical voltages for such nonpolar or semipolar grown laser diode chips are no better than for corresponding polar grown laser diode chips.

[0008] In addition to the standard stainless steel TO packages, TO packages are also known which, for better heat dissipation, have a base based on copper or a copper core and a steel surface, as described, for example, in German patent DE 1 184 870 A, and which are intended to lead to an improvement in heat dissipation from laser diode chips due to the good thermal conductivity of copper.

[0009] In Fig. Figure 1B shows measurements of the optical output power P (in watts) and the operating voltage U (in volts) of laser diode chips in different TO packages as a function of the operating current I (in amperes), based on investigations by the inventors. Curves 1005 and 1007 show the current-dependent optical power and the associated operating voltage of a blue-emitting GaN laser diode chip in a standard TO56 package with a steel base plate and a copper stem, while curves 1006 and 1008 show corresponding measurements for a laser diode chip in an alternative TO56 package with a steel-clad copper base and a steel-clad copper stem. As can be readily seen, the alternative package, which has a steel-clad copper base, does not automatically lead to an improvement in the maximum power of the laser diode chips.Therefore, no laser diode manufacturer pursued the approach of such alternative TO packages for nitride-based laser diodes.

[0010] The publication JP 2005 - 101 073 A describes heat sinks with a flat part, each consisting of a base, a copper layer and an iron coating.

[0011] The publication DE 10 2005 053 274 A1 describes a process for manufacturing a plurality of semiconductor chips and semiconductor components, using a solder layer whose thickness is specified as between approximately 1 µm and approximately 7 µm.

[0012] The publication JP 2 560 131 B2 describes a copper-based TO package with a steel coating.

[0013] The publication JP 2011 - 151 080 A describes enclosures with mounting parts that increase in cross-section towards a mounting surface of the enclosure in order to achieve improved heat dissipation.

[0014] Document US 2012 / 0 057 612 A1 describes a faceted coating with a crystalline layer.

[0015] Document US 2009 / 0 200 573 A1 describes a light-emitting element and a method for its manufacture.

[0016] At least one function of certain embodiments is to specify a laser diode device.

[0017] This problem is solved by an object according to the independent patent claim. Advantageous embodiments and further developments of the object are characterized in the dependent claims and are further described in the following description and drawings.

[0018] The laser diode device features: a housing comprising a housing part and a mounting part connected to the housing part, which extends away from the housing part along a direction of extension, and a laser diode chip on the mounting part, which has semiconductor layers on a substrate with an active layer for emitting light, where the housing part and the mounting part have a base body made of copper and at least the housing part is steel-clad, A first solder layer with a thickness of greater than or equal to 3 µm is arranged between the laser diode chip and the mounting part. The laser diode chip is based on a nitride compound semiconductor material and has a non-polar or semi-polar crystal structure, and the first solder layer has a soft solder based on indium.

[0019] According to at least one embodiment, a laser diode device comprises a housing in which a laser diode chip is arranged. The housing, in particular, comprises a housing part and a mounting part connected to the housing part, which extends away from the housing part along a direction of extension. In other words, the mounting part projects from the housing part and can, for example, be cone-shaped. The mounting part has a mounting surface that extends away from the housing part along the direction of extension of the mounting part and on which the laser diode chip is arranged. The housing part can, in particular, be designed and configured so that a housing cover can be arranged on the housing part for closing the housing.

[0020] The housing component and the mounting component, which may also be formed as a single piece, each have a copper base body, or, in the case of a single-piece design, a common copper base body. At least the housing component is further encased in steel. This means that the housing component is essentially formed from the copper of the base body and covered with a steel layer. The steel layer can, for example, be made of stainless steel.

[0021] Furthermore, the housing component may, for example, have holes or openings through which electrical leads, for example in the form of contact pins, can protrude from the side of the housing component facing away from the mounting component to the side on which the mounting component is located. The electrical leads may be intended for electrical contact with the laser diode chip, for example via a wire connection between an electrical lead and the laser diode chip.

[0022] According to a further embodiment, in addition to the housing part, the mounting part is also encased in steel. In particular, in this embodiment, the housing part and the mounting part can have a common copper base body covered with a layer of steel.

[0023] In particular, the package can be designed as a so-called TO package, for example, with a size of TO38, TO56, or TO90. The package part can also be referred to as a "base plate" and the mounting part as a "stem." Compared to commonly used standard TO packages, which have at least one package part or one package part and one mounting part that are essentially made of steel and do not have a copper-based base, the package described here has higher thermal conductivity due to the copper in the steel-clad package part.

[0024] According to a further embodiment, the housing has a housing cover that is mounted on the housing part and welded to it. It is particularly advantageous for the housing part to be encased in steel, as this allows the housing cover to be welded to the housing part, similar to a standard TO housing with a steel base. The mounting part projects from the housing part into the housing cover along its direction of extension, so that when the housing cover is mounted, the laser diode chip is located on the mounting part in the cavity formed by the housing cover and the housing part. The housing cover also has a window on a side facing away from the housing part, through which the light emitted by the laser diode chip during operation can be emitted from the laser diode device. The housing cover can, for example, be made of steel, particularly stainless steel, or be entirely made of steel except for the window.By welding the housing part to the housing cover, which is designed in the form of a cap over the mounting part and thus also over the laser diode chip on the mounting part, the housing can be hermetically or at least very tightly sealed.

[0025] According to a further embodiment, the laser diode chip is arranged on the mounting part by means of a first solder layer. This means, in particular, that the first solder layer is arranged between the laser diode chip and the mounting part. The first solder layer has a thickness of greater than or equal to 3 µm. Preferably, the thickness of the solder layer can also be greater than or equal to 5 µm.

[0026] The laser diode chip can be mounted directly onto the mounting part using the first solder layer. Alternatively, a thermal interface material, also known as a heat spreader, can be positioned between the laser diode chip and the mounting part. This heat interface material serves to widen or spread the heat flow between the laser diode chip and the mounting part, thereby maximizing the contact area for heat transfer into the housing, particularly the mounting part. Furthermore, the heat interface material can also compensate for stresses between the laser diode chip and the housing, which might be caused, for example, by differing coefficients of thermal expansion.

[0027] According to another embodiment, the thermal interface material is attached to the mounting part by a first solder layer. The laser diode chip is attached to the thermal interface material by a second solder layer. For example, the second solder layer can also have a thickness of greater than or equal to 3 µm, and preferably greater than or equal to 5 µm. Features and advantages described in connection with the first solder layer can also apply to the second solder layer, and vice versa.

[0028] According to another embodiment, the thermal interface material comprises or consists of silicon carbide (SiC), boron nitride (BN), copper tungsten (CuW), or diamond. Silicon carbide, boron nitride, copper tungsten, and diamond can be characterized by particularly high thermal conductivity. Alternatively, the thermal interface material can also comprise aluminum nitride.

[0029] In the laser diode device described here, one or more materials with different coefficients of thermal expansion can be located between the base body of the copper-based mounting part and the laser diode chip, which typically have different coefficients of thermal expansion. These materials include, in particular, the first solder layer, and further, for example, a steel casing of the mounting part and / or one or more additional solder layers and / or a thermal interface material. This can lead to thermally induced stresses during operation between the laser diode chip and the housing, or between the laser diode chip and the thermal interface material, as well as between the thermal interface material and the housing, which can negatively affect the operation of the laser diode device.While it is common practice in the prior art to keep the thickness of the solder layer used to mount a laser diode chip as thin as possible, particularly below 2 µm, to achieve optimal heat dissipation, the laser diode device described here uses a significantly thicker first solder layer and, if necessary, a second solder layer as well. The higher thermal resistance of such a solder layer is accepted because such a thick layer has proven advantageous in compensating for thermally induced stresses between the housing and the laser diode chip. For example, the solder layer described here can be an indium-based soft solder to particularly well compensate for differing thermal expansions.In the laser diode device described here, it is therefore possible to use materials such as silicon carbide, boron nitride, copper tungsten or diamond as a heat conducting element, which have a higher thermal conductivity compared to aluminum nitride but also significantly different coefficients of thermal expansion compared to the usual materials for laser diode chips.

[0030] According to another embodiment, the laser diode chip is based on a nitride compound semiconductor material. The laser diode chip can, in particular, have a substrate, preferably an electrically conductive substrate, for example, crystalline (In,Al,Ga)N. An epitaxial layer sequence, i.e., epitaxially grown semiconductor layers, can be deposited on top of this substrate. This sequence is based on a nitride compound semiconductor material and is therefore based on InAlGaN.

[0031] InAlGaN-based compound semiconductor materials, (In,Al,Ga)N-based compound semiconductor materials, and nitride compound semiconductor materials include, in particular, those that contain a material from the III-V compound semiconductor material system In x Al y Ga 1-x-y The laser diode chip can have N with 0 ≤ × ≤ 1, 0 ≤ y ≤ 1 and × + y ≤ 1, for example, GaN, AlN, AlGaN, InGaN, AlInGaN. The laser diode chip can, in particular, have a sequence of semiconductor layers on the substrate, which includes an active layer, especially preferably based on AlGaInN and / or InGaN, which is designed to emit light during operation. In particular, the laser diode chip can emit light in an ultraviolet to green wavelength range during operation.

[0032] According to a further embodiment, the laser diode chip has semiconductor layers on the substrate, which, for example, form the active layer between waveguide layers and cladding layers. In particular, a first cladding layer, a first waveguide layer above it, the active layer above it, a second waveguide layer above it, and a second cladding layer above this. A semiconductor contact layer and an electrical connection layer, for example in the form of a metal layer, can further be arranged above the second cladding layer. The electrical contact of the laser diode chip can particularly preferably be made via the electrical connection layer opposite the substrate as well as via the conductive substrate itself, wherein the substrate can also have an electrical connection layer on the side facing away from the semiconductor layers.On the side of the active layer facing away from the substrate, a charge carrier barrier layer can be arranged between the waveguide layer and the cladding layer to prevent a so-called charge carrier overshoot.

[0033] For example, the semiconductor layers arranged between the substrate and the active layer can be n-doped, and the semiconductor layers arranged above the active layer (from the substrate's perspective) can be p-doped. Alternatively, the doping order can be reversed. The active layer can be undoped or n-doped. The laser diode chip can, for example, have a conventional pn junction, a double heterostructure, or a quantum well structure as its active layer, particularly preferably a multiple quantum well (MQW) structure. Within the scope of this application, the term quantum well structure includes, in particular, any structure in which charge carriers can undergo quantization of their energy states by confinement. In particular, a quantum well structure can include quantum wells, quantum wires, and / or quantum dots, and a combination of these structures.For example, the active layer can feature InGaN-based quantum films between suitably designed barrier layers.

[0034] According to a further embodiment, the laser diode chip, as described above, is based on a nitride compound semiconductor material and has a non-polar or semi-polar crystal structure. Nitride compound semiconductor materials have a wurtzite lattice structure and are usually grown such that the growth direction corresponds to the crystallographic c-axis and thus the growth plane corresponds to the

[0001] crystal plane. This growth leads to a polar crystal structure, which generates internal piezoelectric fields in the semiconductor crystal, causing internal polarization. This makes the injection of charge carriers into the active layer and the distribution of charge carriers in the active layer more difficult. As described in the publication by U. Strauss et al., physica status solidi, Vol. 248, p.As described in pp. 652-657, 2010, simulations of polar crystal structures show that in a polar crystal structure with an active layer and a quantum well structure with quantum films, injection barriers of several hundred mV per quantum film can arise, depending on the emission wavelength of the quantum films. The publication by D. Sizov et al., IEEE Journal of Selected Topics in Quantum Electronics, Vol. 17, No. 5, pp. 1390-1401, 2011, describes a reduction of the injection barriers through semipolar crystal interfaces.

[0035] Hereinafter, “non-polar” or “semi-polar” crystal structures are defined as those whose growth direction, and thus their vertical current direction during operation, deviates from the crystallographic c-axis of the nitride compound semiconductor material and, in particular, is not parallel, and which therefore have a growth plane that deviates from and is not parallel to the

[0001] plane. Examples of non-polar crystal structures are the following directions or growth planes: [1-100], [11-20], and all crystal planes between these. Semi-polar planes are all crystal planes between the

[0001] plane and a non-polar crystal plane. A non-polar or semi-polar crystal structure can be achieved, for example, by growing the semiconductor layers on a non-polar or semi-polar substrate surface.

[0036] The non-polar or semi-polar crystal structure of the laser diode chip may thus make it possible to reduce the voltage drop and therefore the power loss in the active layer of the laser diode chip compared to a laser diode chip based on a nitride compound semiconductor material with a polar crystal structure. However, forward voltages lower than those of LED chips with polar crystal structures have not yet been achieved with laser diode chips with non-polar or semi-polar crystal structures at the same current. The inventors attribute this to a higher contact resistance, particularly on the side of the semiconductor layers facing away from the substrate, towards the electrical connection layer.In the case of a p-doped semiconductor contact layer on the side of the active layer facing away from the substrate, this can be attributed, for example, to the difficult p-doping of nitride compound semiconductor materials.

[0037] In particular, the laser diode chip described here can be designed such that, compared to a laser diode chip based on a nitride compound semiconductor material with a polar crystal structure, it exhibits higher power dissipation in the semiconductor layers on the side of the active layer facing away from the substrate and lower power dissipation in the active layer during operation than the laser diode chip based on a nitride compound semiconductor material with a polar crystal structure.

[0038] As described above, using a copper-based package, such as a TO package, or one with a copper core and a steel surface, does not, in itself, improve laser power compared to using a standard stainless steel TO package. Similarly, using laser diode chips with a non-polar or semi-polar crystal structure in a nitride compound semiconductor material does not improve forward voltage. Furthermore, using a solder layer 3 µm thick or greater appears to be counterproductive due to the higher thermal resistance.

[0039] However, the inventors recognized that the combination of the above-described housing with the copper substrate, the laser diode chip based on a nitride compound semiconductor material with a non-polar or semi-polar crystal structure, and the first solder layer with a thickness of 3 µm or greater is particularly advantageous for achieving higher output powers compared to known laser diode devices. In contrast to the prior art of other laser systems, such as GaAs-based laser diode chips in TO packages, the inventors recognized the advantage of generating a large temperature gradient during operation within the laser diode chip, which is made possible by the targeted selection and combination of the laser diode device components described here.In particular, the different power dissipation distribution compared to a conventional laser diode chip based on a nitride compound semiconductor material with a polar crystal structure, and the copper of the housing base, result in a large temperature gradient within the laser diode chip and, conversely, a small temperature gradient within the housing material. The good thermal conductivity of the copper base, as described above, is not advantageous on its own but rather in combination with the laser diode chip described here. Furthermore, the combination of the housing described here with the laser diode chip described here is made possible by the use of a significantly thicker first solder layer compared to the prior art, which would otherwise appear counterproductive in terms of its higher thermal resistance.

[0040] Furthermore, it is advantageous in the laser diode device described here to increase the area of ​​the active layer of the laser diode chip compared to known laser diode chips. In particular, the active layer can have an area of ​​greater than or equal to 10,000 µm². 2 and preferably of greater than or equal to 20000 µm 2 up to 30000 µm 2 exhibit. A drop in current density from a maximum value to 10% is assumed as the area limitation.

[0041] As described above, simply increasing the area of ​​the active layer is counterproductive with regard to achieving a higher output power of the laser diode chip. However, the inventors recognized that only by combining this with the previously described temperature gradient within the laser diode chip can a higher output power be achieved, made possible by the larger area of ​​the chip generating the laser light. The temperature gradient within the laser diode chip, in turn, can only be achieved by reducing heat generation and improving heat dissipation within and from the active layer, combined with a hotter electrical contact on the side of the active layer facing away from the substrate, compared to the prior art.

[0042] The deterioration of the electrical contact on the side of the active layer facing away from the substrate—i.e., the deliberate introduction of higher power dissipation compared to the prior art—is not only compensated for by the lower losses in the active layer, but is more than compensated for by the possibility of high-current operation, for example, through a larger area of ​​the active layer, and the precisely controlled temperature gradient in the laser diode chip. Thus, the combination of the measures described here results in a significant improvement in the form of increased output power compared to the prior art. In the laser diode device described here, a higher optical output power in the range of several watts, particularly more than 3 W, as well as a higher conversion efficiency of electrical input power to optical output power, can be achieved.

[0043] According to a further embodiment, the mounting part has a cross-section perpendicular to its direction of extension that projects, at least on one side, to a housing cover arranged above the mounting part and attached to the housing part. In other words, the mounting part is thick enough in a plane perpendicular to its direction of extension to reach the housing cover. A gap may still exist between the mounting part and the housing cover. Alternatively, the mounting part may also touch the housing cover. It is particularly advantageous if the mounting part extends to the housing cover over as large an area as possible.

[0044] According to a further embodiment, the housing part and the housing cover have a circular cross-section in a plane perpendicular to the direction of extension of the mounting part. The mounting part can advantageously have a cross-section in a plane perpendicular to the direction of extension that occupies more than a semicircular segment, i.e., more than a semicircular area. The thicker the mounting part is, and thus the larger its cross-sectional area perpendicular to the direction of extension, the greater the heat dissipation through the housing. The space within the housing cover not occupied by the mounting part is provided for mounting the laser diode chip.

[0045] Furthermore, it is also possible that the cross-section of the mounting part increases in the direction of the housing part. For example, the mounting part can have a wedge-shaped cross-section in a plane along its direction of extension, thus becoming wider and / or thicker relative to a mounting plane on which the laser diode chip is arranged. Compared to a standard TO package, the laser diode chip on such a mounting part can emit light in an oblique direction, which, for example, allows the mounting part to have the greatest possible thickness and width without being obscured by the housing cover window.

[0046] To compensate for the oblique emission direction of a wedge-shaped cross-section of the mounting part, the housing part can have a wedge-shaped cross-section in a plane parallel to the direction of extension. Alternatively or additionally, the connection angle between the housing part and the mounting part can also be other than 90°, where a connection angle of 90° corresponds to the standard arrangement of a mounting part on a housing part of a standard TO package. This ensures that, despite the oblique emission direction from the laser diode chip, the laser diode device can emit the light generated by the laser diode chip at approximately a right angle to a mounting surface of the housing, which allows the laser diode device to be mounted on a substrate such as a printed circuit board.Alternatively, it is also possible, for example, to attach an auxiliary ring to the housing part, which allows for an angled mounting of the housing and thus of the laser diode device.

[0047] According to a further embodiment, the laser diode chip has a radiation output surface through which the light generated in the active layer is emitted during operation. The laser diode chip is preferably designed as an edge-emitting laser diode chip, in which the radiation output surface can be generated, for example, by fracturing, splitting, and / or etching a semiconductor layer composite along a crystal plane. Furthermore, the laser diode chip has a back surface arranged opposite the radiation output surface. The radiation output surface can, in particular, be a region of a front surface of the laser diode chip through which the coherent light generated in the laser diode chip is emitted. The front surface, and especially the radiation output surface, and the back surface are also commonly referred to as facets in edge-emitting laser diode chips.Furthermore, the laser diode chip has side surfaces that connect the back surface and the radiation output coupling surfaces and are formed by the sides of the semiconductor layers in a direction perpendicular to the growth and arrangement direction of the semiconductor layers.

[0048] According to another embodiment, the laser diode chip has a crystalline protective layer, at least on the radiation output surface. Here and in the following, a "crystalline" layer is defined as a layer that exhibits a crystalline structure throughout, i.e., both short-range and long-range order. In contrast, an amorphous layer exhibits only short-range order, and a semi-crystalline or partially crystalline layer exhibits long-range order only in parts or areas, which does not extend across the entire layer.

[0049] In particular, the crystalline protective layer can be hermetically sealed, especially in the area of ​​the radiation output coupling surface, i.e., preferably the area of ​​the front surface of the laser diode chip from which the laser radiation is emitted during operation. A hermetically sealed layer can, in particular, have a density sufficiently high to protect the area of ​​the laser diode chip covered by the hermetically sealed layer throughout the lifetime of the laser diode chip and the laser diode device in such a way that no damage occurs that would shorten the lifetime. In particular, the crystalline protective layer can have a higher density than, for example, an amorphous or a partially crystalline layer. This can be due, for example, to the fact that the crystalline layer is preferably formed without lattice defects, so-called "pin holes," which can cause leaks.

[0050] The crystalline protective layer can protect the areas of the laser diode chip covered by the crystalline protective layer, i.e., at least the radiation output surface, from environmental influences such as damaging gases. Such environmental influences can be caused, for example, by oxygen, ozone, substances contained in acid rain, and other chemicals. For instance, when the laser diode device is used as a light source in automotive engineering, an unprotected laser diode chip can be at risk from aggressive media such as hydrocarbons and sulfur and nitrogen compounds, for example, hydrogen sulfide and sulfur and nitrogen oxides, which can damage the laser diode chip and, in particular, its radiation output surface.Such damaging environmental influences can penetrate the housing of the laser diode device, reaching the laser diode chip, for example, if the housing itself is not hermetically sealed from the environment. Due to differing coefficients of thermal expansion, the housing of the laser diode device described here presents a particular technical challenge: ensuring a sufficiently tight weld between the copper or steel-clad copper housing and a steel-based housing cover. Especially in high-volume production of such components, the escape rate of components exhibiting residual leakage can increase.While it is known to coat the facets of laser diode chips, these coatings are typically amorphous to partially crystalline and, due to their grain boundaries and defects, can only inadequately prevent the diffusion of facet-damaging materials. The crystalline protective layer thus provides additional protection, particularly for the critical radiation output surface, ensuring the reliable operation of the laser diode device.

[0051] Furthermore, the thick solder layers described here between the laser diode chip and the housing, for example, the first solder layer, can cause solder particles to migrate across the surfaces of the laser diode chip, particularly in the areas of the laser facets. Without a sufficiently dense facet coating, the solder particles can diffuse through the facet coating, potentially leading to leakage currents across the laser facets. The crystalline protective layer described here ensures a sufficiently dense facet coating, preventing damage to the laser diode chip from solder particles. In the case of a crystalline dielectric material, the crystalline protective layer can also significantly increase the breakdown field strength, thus providing protection against electrical breakdown, for example, due to a raised solder layer or p-metallization extending over the facet.

[0052] According to a further embodiment, the laser diode chip is provided with the crystalline protective layer, at least on the radiation output coupling surface, during the manufacture of the laser diode device. For this purpose, a deposition method is used that allows the production of a crystalline dielectric, semiconducting, or conductive layer. For example, a chemical vapor deposition (CVD) process at elevated temperatures can be selected, particularly at temperatures greater than or equal to 500°C and preferably greater than or equal to 600°C. The crystalline protective layer can also preferably be deposited by means of an atomic layer deposition (ALD) process, in particular an atomic layer epitaxy (ALE) process.Atomic layer deposition processes can also be carried out at higher temperatures of 500°C or more, and preferably 600°C or more, compared to conventional manufacturing methods for faceted coatings, in order to obtain the crystalline protective layer. Advantages of the aforementioned processes, particularly atomic layer deposition, include a defect-free, pinhole-free structure, good adhesion to surfaces, high stability, good conformability even to irregularities with a large aspect ratio, and a low-stress structure. A particularly advantageous feature of such protective layers is their low permeability to gases, such as oxygen or humid air, as described, for example, in the publications by P.F. Carcia et al., Journal of Applied Physics 106, 023533 (2009) and T. Hirvikorpia, Applied Surface Science 257, 9451-9454 (2011).

[0053] According to another embodiment, the crystalline protective layer comprises exactly one crystalline layer. Alternatively, it is also possible for the crystalline protective layer to comprise a plurality of crystalline layers. The plurality of crystalline layers can, for example, be formed by several crystalline layers made of different materials. Furthermore, it is also possible for the plurality of crystalline layers to be formed by an alternating sequence of at least two crystalline layers made of different materials.

[0054] According to another embodiment, an optical layer is applied to the radiation output coupling surface. The optical layer can, for example, be a reflective or antireflective coating. Such optical layers typically have one, and preferably several, layers of transparent materials that can form a periodic sequence of different refractive indices.

[0055] For example, the crystalline protective layer can form the optical layer. This can be particularly advantageous if the crystalline protective layer comprises multiple crystalline layers. Alternatively, an optical layer can be applied in addition to the crystalline protective layer. This optical layer is not necessarily crystalline, but can be, for example, amorphous or partially crystalline. In this case, the optical layer can be applied using a conventional application method, such as those known from the prior art for facet coatings.

[0056] The optical layer can, for example, be positioned between the radiation output surface and the crystalline protective layer and covered by the crystalline protective layer. This allows the optical layer to be protected by the crystalline protective layer in addition to the radiation output surface. Alternatively, the crystalline protective layer can be positioned between the radiation output surface and the optical layer. In this case, the crystalline protective layer is advantageously located as close as possible to, and preferably directly on, the laser diode chip, i.e., at least on the radiation output surface. In combination with an additional optical layer, the crystalline protective layer can also incorporate some of the optical functionality of the coating and thus be part of the optical layer itself.

[0057] According to another embodiment, the crystalline protective layer is formed by a dielectric material or at least comprises a dielectric material. A dielectric layer is particularly advantageous when directly coating the radiation output coupling surface and, optionally, other surfaces of the laser diode chip, as this prevents short circuits of the laser diode chip. In combination with an optical layer or a passivation layer between the crystalline protective layer and the laser diode chip, the crystalline protective layer can also comprise or be composed of a semiconducting or conductive material.

[0058] The crystalline protective layer can preferably be formed by an oxide or at least comprise an oxide. The oxygen in the oxide material can, for example, form hydrogen bonds with water molecules, thereby preventing the water molecules from penetrating the crystalline layer. The oxide can particularly preferably be dielectric.

[0059] Particularly preferably, the crystalline protective layer can comprise one or more crystalline layers of one or more of the following materials: Al2O3, Si3N4, Nb x Al y O z, Al2O3 / TiO2, Al2O3 / Ta2O5, HfO2, Ta2O5 / ZrO2, Ta2O5, Ta x Ti y O z , Ta2O5 / NbO5, TiO2, ZrO2, HfO2, Ta2O5, Nb2O5, Sc2O3, Y2O3, MgO, B2O3, SiO2, GeO2, La2O3, CeO2, PrO x , Nd2O3, Sm2O3, EuO x, Gd2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3, SrTiO2, BaTiO3, PbTiO3, PbZrO3, Bi x Ti yO, Bi x Si y O, SrTa2O6, SrBi2Ta2O9, YScO3, LaAlO3, NdAlO3, GdScO3, LaScO3, LaLuO3, Er3Ga5O 13 , HfSiO, HfTiO, AlSiO, LaAlO, LaHfO, In2O3, ZnO, Ga2O3, V2O5, HfAlO, HfTaO, HfZrO, Ru, Pt, Ir, Td, Rh, Ag, W, Cu, Co, Fe, Ni, Mo, Ta, Ti, Al, Si, Ge, In2O3, In2O3:Sn, In2O3:F, In2O3:Zr, SnO2, SnO2:Sb, ZnO:Al, ZnO:B, ZnO:Ga, RuO2, RhO2, IrO2, Ga2O3, V2O5, WO3, W2O3, BN, AlN, GaN, InN, SiN x Ta3N5, Cu3N, Zr3N4, Hf3N4, NiO, CuO, FeO x CrO x CoO x , MnO x TiN, Ti x Si y N z , NbN, TaN, Ta3N5, MoN x , W2N, GaAs, AlAs, AlP, InP, GaP, InAs, TaC.

[0060] According to another embodiment, a crystalline protective layer is also applied to the back surface of the laser diode chip opposite the radiation output surface. This crystalline protective layer on both the radiation output surface and the back surface effectively protects the facets of the laser diode chip, which are sensitive to environmental influences.

[0061] An optical layer, particularly a reflective coating, can also be applied to the back surface. As described above for the coating of the radiation output coupling surface, the optical layer can also be arranged between the crystalline protective layer and the back surface. Alternatively, the crystalline protective layer can also be arranged between the optical layer and the back surface. It can also be particularly advantageous if the optical layer on the back surface of the laser diode chip is formed by the crystalline protective layer.

[0062] According to a further embodiment, one or more crystalline protective layers are applied to the side surfaces of the laser diode chip that connect the back surface and the radiation output surface. In particular, it can be advantageous if a crystalline protective layer is applied to all side surfaces arranged perpendicular to the growth and arrangement direction of the semiconductor layers, as well as to the facets of the laser diode chip, so that the semiconductor layers and the interfaces between semiconductor layers are protected all around.

[0063] Further advantages, advantageous embodiments and further developments result from the exemplary embodiments described below in conjunction with the figures.

[0064] They show: Fig. 1A and Fig. 1B Measurements for conventional laser diode devices, Fig. 2A and Fig. 2B Schematic representations of a laser diode device according to an exemplary embodiment, Fig. 3 a schematic representation of a laser diode chip according to an exemplary embodiment, Fig. 4 to 5B Measurements of laser diode devices, Fig. Figures 6 to 9 show schematic representations of laser diode devices according to further embodiments and Fig. 10 to 16 schematic representations of parts of laser diode devices according to further embodiments.

[0065] In the exemplary embodiments and figures, identical, similar, or similarly functioning elements may be designated with the same reference numerals. The depicted elements and their relative sizes are not to be considered to scale; rather, individual elements, such as layers, components, building elements, and areas, may be exaggerated for clarity and / or better understanding.

[0066] In the Fig. 2A, Fig. Figure 2B shows an embodiment of a laser diode device 100, wherein in Fig. 2A a schematic sectional view and in Fig. 2B a top view of the front of the laser diode device 100 opposite the one in Fig. 2A shows direction 110. The following description applies equally to the Fig. 2A and Fig. 2B.

[0067] The laser diode device 100 has a housing 1, which is designed in the form of a so-called TO package. The housing 1 comprises a housing part 10 and a mounting part 11 arranged on the housing part. The mounting part 11 extends from the housing part 10 along the direction of extension 110 and, in the illustrated embodiment, is formed integrally with the housing part 10. For this purpose, the housing part 10 and the mounting part 11 have a base body made of copper. The housing part 10 further comprises a steel sheath 12, which is formed by a coating of the copper base body in the area of ​​the housing part 10.

[0068] Furthermore, the housing part 10 can, for example, have holes or openings in which connecting leads are arranged, projecting from the side of the housing part 10 facing away from the mounting part 11 towards the side of the mounting part 11. Connecting leads arranged and secured therein can, for example, be designed as electrical feedthroughs and provide possibilities for electrical contacting.

[0069] The mounting part 11 has a mounting surface 13 on which a laser diode chip 2 is arranged. In particular, the laser diode chip 2 is mounted on the mounting surface 13 of the mounting part 11 via a first solder layer 3 and is thereby electrically and thermally connected to the housing 1.

[0070] A housing cover 14, indicated by the dashed lines, can be arranged over the mounting part 11 and thus over the laser diode chip 2. The housing cover 14, which may also have a window 15, can be made of steel, for example, and preferably is made entirely of steel except for the window 15. Because the housing part 10 has the steel casing 12, the housing cover 14 can be placed on the housing part 10 of the housing 1 and attached by welding in a standard process, as with conventional TO packages with steel bases. Furthermore, welding the housing cover 14 to the casing 12 of the housing part 10 preferably achieves the tightest possible connection, thereby protecting the laser diode chip 2 from damaging environmental influences.

[0071] As from Fig. As can be seen in Figure 2B, the housing part 10 and the housing cover 14 are circularly formed in a plane perpendicular to the direction of extension 110. The mounting part 11, in the illustrated embodiment, has a cross-section that covers more than a semicircular segment, i.e., more than a semicircular area. Furthermore, the mounting part 11 projects to the housing cover 14 on the side facing away from the mounting surface 13. This allows the mounting part 11 to be made as thick as possible in cross-section, thereby achieving high thermal conductivity.

[0072] While it is common practice in standard laser diode devices to couple a laser diode chip to a housing via the thinnest possible solder layer to achieve the lowest possible thermal resistance for optimal heat dissipation, the first solder layer 3 in the embodiment shown here has a thickness of greater than or equal to 3 µm and preferably greater than or equal to 5 µm. This allows thermally induced stresses that occur during operation due to the heat generated in the laser chip 2 and the different coefficients of thermal expansion of the laser diode chip 2 and the housing 1 to be compensated. Furthermore, such a thick solder layer can also compensate for surface irregularities on the mounting surface 13 of the mounting part 11. These irregularities can occur, in particular, when the mounting part 11, as shown below, Fig. Figure 6 shows how the housing part 10 has a steel casing 12.

[0073] The laser diode chip 2 is preferably as shown in Fig. Figure 3 shows a laser diode chip with an edge-emitting surface 27 formed by a side surface and a rear surface 28 opposite the radiation-emitting surface. The radiation-emitting surface 27 can, in particular, be formed by the region of the front surface of the laser diode chip 2, through which the laser radiation generated in the laser diode chip 2 is emitted during operation.

[0074] In particular, the laser diode chip 2 is based on a nitride compound semiconductor material. The laser diode chip 2 has a substrate 20, which is preferably electrically conductive and, for example, comprises or is made of crystalline (In,Al,Ga)N. A sequence of semiconductor layers based on a nitride compound semiconductor material is grown on this substrate, preferably by means of an epitaxial growth process such as metal-organic vapor phase epitaxy (MOVPE). The laser diode chip 2 has an active layer 23 on the substrate 20, which is arranged between waveguide layers 22 and cladding layers 21. In particular, the laser diode chip 2 has a first cladding layer 21 on the substrate 20, on which a first waveguide layer 22 and, above it, the active layer 23 are arranged.Above the active layer 23, in the growth direction, there is another waveguide layer 22, followed by another cladding layer 21, and above that a semiconductor contact layer 24, which is contacted by an electrical connection layer 25, for example in the form of a metallic electrode layer. The electrical connection of the laser diode chip 2 is made via the electrical connection layer 25 and the electrically conductive substrate 20, which may have another electrical connection layer on the side facing away from the semiconductor layers 21, 22, 23, 24 (not shown).

[0075] In the illustrated embodiment, the semiconductor layers facing the substrate 20, viewed from the active layer 23, are n-doped, while the semiconductor layers on the side of the active layer 23 facing away from the substrate 20 are p-doped. Alternatively, the doping order can be reversed. The active layer 23 can, for example, be n-doped or undoped and, in particular in the illustrated embodiment, may have a multiple quantum well structure.

[0076] The copper-based housing 1 achieves, in particular, improved thermal conductivity compared to a standard TO housing made of steel. Fig. Figure 4 shows the optical output power P (in watts) and curves 403 and 404 the operating voltage U (in volts), each as a function of the operating current I (in amperes), for blue-emitting GaN-based laser diode chips. The laser diode chips were examined in standard TO56 packages with a steel base and in copper-based packages described here, with a copper housing made of steel and mounted using a solder layer thickness of approximately 5 µm. A comparison of curves 401 and 403 for the copper-based package and thick solder layer described here with curves 402 and 404 for the standard TO package and thin solder layer shows an improvement in output power when using the package with the first solder layer described here, despite the higher thermal resistance of the thicker solder.

[0077] In order to achieve the highest possible output power for the light emitted by the laser diode chip 2 during operation, according to a further embodiment, which is also based on the Fig. 2A, Fig. 2B and Fig. As explained in section 3, certain temperature gradients are generated in the laser diode device 100. In particular, a minimum temperature gradient exists in the housing 1, which is achieved through the copper-based base body of the housing 1.

[0078] In contrast to the housing 1, which is designed to have the highest possible thermal conductivity to generate the lowest possible temperature gradient within the housing 1, the laser diode chip 2 is designed such that the electrical connection layer 25 and the substrate 20 have the largest possible temperature gradient. To achieve such a targeted temperature gradient, the laser diode chip 2 and the housing 1 must be matched. Investigations by the inventors have shown, in particular, that electrical losses in the laser diode chip 2 must be considered separately. Firstly, the voltage drop across the top contact, which in the illustrated embodiment is designed as a p-doped contact, in the region of layers 26, must be taken into account. This voltage drop is caused by the difficult p-doping properties of the nitride semiconductor material system.

[0079] In Fig. The electrical voltage of a nitride-based polar laser diode chip 2 in a TO package is shown for various temperatures (in °C) at an operating current of 1 ampere in a pulsed mode with a pulse length of 1 µs and a duty cycle of 1%. Fig. Figure 5B shows the operating voltage U (in volts) as a function of the operating current I (in amperes) for a laser diode device with a copper-based package (curve 501) compared to a laser diode device with a standard TO56 steel package (curve 502). The operating voltage increases in the copper-based package, suggesting that the layers 26 are cooler in the case of curve 501 than in the case of curve 502 due to improved heat dissipation.

[0080] Secondly, the voltage drop in the underlying layers, and especially in the active layer 23, must be taken into account. Since the active layer 23 in the illustrated embodiment is designed as a multi-quantum well structure with a layer stack of light-generating quantum films, a voltage drop occurs particularly at the interfaces of the quantum well structure. The laser diode chip 2 is designed such that, with almost the same power dissipation as standard laser diode chips, electrical barriers and resistances near the top-side contact are accepted, and losses near or below the active layer 23 are minimized.

[0081] For this purpose, the laser diode chip 2 is designed as a laser diode chip based on a nitride compound semiconductor material and has a non-polar or semi-polar crystal structure, which is described in the general section. Due to the non-polar or semi-polar crystal structure of the laser diode chip 2, it is possible to achieve, in comparison to standard laser diode chips based on a nitride compound semiconductor material and having a polar crystal structure, a higher power dissipation during operation on the side of the active layer 23 facing away from the substrate 20, i.e., in layers 26, while a lower power dissipation is achieved in the active layer 23.

[0082] The deterioration of the electrical contact in the region of layers 26 above the active layer 23 due to higher electrical power dissipation compared to a conventional laser diode chip based on a nitride compound semiconductor material with a polar crystal structure is not only compensated for by the lower losses in the active layer 23. Rather, overcompensation is achieved through possible high-current operation and the specifically controlled temperature gradient in the laser diode chip 2. Thus, the combination of the housing 1 with the non-polar or semi-polar laser diode chip 2 and the first solder layer 3 described here results in a significant improvement compared to known laser diode devices.

[0083] It is particularly advantageous if the chip area of ​​the laser diode chip 2 described here is increased compared to known laser diode chips; in particular, current injection into the active layer 23 on an area greater than or equal to 10000 µm is possible. 2 and preferably of greater than or equal to 20,000 to 30,000 µm 2 Advantageously, a drop in current density from a maximum value to 10% of this value is assumed as the area limitation. Due to the previously described measures, which lead to the largest possible temperature gradient in the laser diode chip 2, i.e., improved heat dissipation from the active layer 23 combined with a hotter top-side contact in the region of layers 26, an increase in the area into which the current is impressed leads to an increase in optical output power compared to the prior art.

[0084] The following figures show further embodiments of laser diode devices, which are modifications and variations of the one described in Fig. 2A, Fig. 2B and Fig. The embodiment shown in Figure 3 is shown. The following description is therefore essentially limited to the differences from the previous embodiment. In particular, the laser diode devices described below may have a housing cover, even if this is not explicitly shown in the figures.

[0085] In Fig. Figure 6 shows an embodiment of a laser diode device 101, in which, compared to the laser diode device 100 according to the Fig. 2A and Fig. 2B not only the housing part 10 but also the mounting part 11 has a steel sheath 12. This allows a steel mounting surface 13 to be achieved, as with a standard TO package, while simultaneously achieving the improved thermal conductivity provided by the copper.

[0086] In the Fig. 7A to 7C is a laser diode device 102 according to a further embodiment in a schematic sectional view ( Fig. 7A), in a supervision contrary to the direction of extension 110 ( Fig. 7B) as well as in a top view of the assembly area 13 ( Fig. 7C). In contrast to the previous embodiments, a heat-conducting element 4 is arranged between the laser diode chip 2 and the mounting part 11 of the housing 1 in the laser diode device 102. The heat-conducting element is designed in particular as a so-called heat spreader and serves to widen the heat flow between the laser diode chip 2 and the mounting part 11 of the housing 1 in order to achieve the largest possible contact area for heat transfer into the housing 1.

[0087] The first solder layer 3, with which the thermal interface element 4 is mounted on the mounting part 11 of the housing 1, can be formed with a thickness of greater than or equal to 3 µm and, more preferably, greater than or equal to 5 µm, as described above. Furthermore, a second solder layer 5 is arranged between the thermal interface element 4 and the laser diode chip 2, with which the laser diode chip 2 is mounted on the thermal interface element 4. The second solder layer 5 can preferably also have a thickness of greater than or equal to 3 µm and, more preferably, greater than or equal to 5 µm. Alternatively, it is also possible that only one of the two solder layers 3, 5 has such a large thickness, for example, only the first solder layer 3.

[0088] The mounting part 11 can be formed from copper, as shown in the illustrated embodiment, or, as in conjunction with Fig. 6 described and in Fig. 7A, indicated by the dashed line, also has a steel casing 12.

[0089] The laser diode chip 2 and the housing 1 have different coefficients of thermal expansion due to the different materials used. Nitride-based semiconductor materials typically have a coefficient of thermal expansion of approximately 5.6 × 10⁻⁶. -6 1 / K and a thermal conductivity of about 100 W / mK, while copper has a coefficient of thermal expansion of about 16...18 × 10 -6 1 / K and a thermal conductivity of approximately 300 W / mK. Between these layers are several materials with similarly different coefficients of thermal expansion, such as a steel casing 12 of the mounting part 11, the solder layers 3 and 5, and the heat-conducting element 4. Steel has a coefficient of thermal expansion of approximately 6...12 × 10 -61 / K and a thermal conductivity of approximately 30...70 W / mK. The thermal conductivity element 4 can, for example, be made of or consisting of AlN, which has a coefficient of thermal expansion of approximately 4.5...5.7 × 10 -6 The thermal expansion coefficient of an AlN thermal conductor 4 is 1 / K and has a thermal conductivity of approximately 80–200 W / mK. The thermal expansion coefficient of an AlN thermal conductor 4 is thus relatively well matched to the thermal expansion coefficient of the laser diode chip 2. However, at the interface between the AlN thermal conductor 4 and the housing 1, i.e., either copper or steel-clad copper, there is a significant difference in the thermal expansion coefficients.

[0090] Particularly preferably, SiC, especially 6H-SiC, can be used as the material for the heat conducting element 4 instead of AlN, which has a coefficient of thermal expansion of about 4.4 × 10 -61 / K but also exhibits a higher thermal conductivity of approximately 200...500 W / mK. Alternatively, one of the following materials can be used as the heat-conducting element 4: CuW with a coefficient of thermal expansion of approximately 6...8 × 10 -6 1 / K and a thermal conductivity of approximately 200...250 W / mK, BN with a coefficient of thermal expansion of approximately 2.5...4 × 10 -6 1 / K and a thermal conductivity of about 600 W / mK, diamond, for example diamond produced by CVD, which has an even higher thermal conductivity of about 1000 W / mK with a coefficient of thermal expansion of 2.3 × 10 -61 / K. Although such materials are rather unfavorable for the thermal conductivity element 4 with regard to thermal stress, they can be preferably used in the laser diode device described here, since the larger thermal stresses caused by these materials can be compensated for by the thick solder layers 3, 5 described here. The solder layers 3, 5 can, for example, have a soft solder based on indium to enable the best possible compensation of the thermally induced stresses.

[0091] In Fig. Figure 8 shows a further embodiment of a laser diode device 103, which, purely by way of example, has a heat conducting element 4 between the laser diode chip 2 and the housing 1, like the laser diode device 102 of the previous embodiment.

[0092] In comparison to the previous embodiments, the laser diode device 103 has a mounting part 11 which has a cross-section perpendicular to the direction of extension 110 that increases in thickness towards the housing part 10, i.e., opposite to the direction of extension 110. For this purpose, the mounting part 11 has a wedge-shaped cross-section in the sectional plane shown, which is higher near the housing part 1 than in areas further away from the housing part 1. In other words, the thickness of the mounting part 11 increases towards the housing part 10.

[0093] Such a wedge-shaped cross-section of the mounting part 11 can be particularly advantageous for achieving the highest possible thermal conductivity and, due to the inclined arrangement of the laser diode chip 2 relative to the indicated housing cover 14 and its window 15, can result in only minimal or no shadowing by the window 15 of the housing cover 14. To ensure a mounting surface for the laser diode device 103 that is oriented perpendicular to the emission direction of the laser diode chip 2, the housing part 10 of the housing 1 also has a wedge-shaped cross-section in the illustrated embodiment. Alternatively, the connection angle between the mounting part 11 and the housing part 10 can also be other than 90° and adapted to the opening angle of the wedge that forms the mounting part 11.Furthermore, it is also possible to attach an auxiliary ring to the housing part 10, which has a corresponding cross-section, so that the housing 1 can be mounted at an angle on a support surface.

[0094] In Fig. Figure 9 shows a further embodiment of a laser diode device 104 in a top view of the mounting surface 13, which additionally or alternatively has a wedge-shaped cross-section of the mounting part 11 with an increasing width in the plane of the mounting surface 13, in addition to or as an alternative to the wedge-shaped cross-section of the mounting part 11 of the previous embodiment.

[0095] Through the in the Fig. 8 and Fig. The increasing height and / or width of the mounting part 11 shown in Figure 9 towards the housing part 10 can, in addition to the design of the housing 1 as a copper-based housing, increase and optimize the thermal conductivity of the housing 1.

[0096] In the following Fig. Figures 10 to 16 show exemplary embodiments of the laser diode chip 2, which can be mounted in a housing 1 of the previously described laser diode devices 100, 101, 102, 103, 104 by means of a solder layer shown in partial view. For the sake of clarity, the layer structure of the laser diode chip 2 is not shown in the following figures.

[0097] The laser diode chip 2 of the following embodiments has a crystalline protective layer 6 on at least one radiation output surface 27, which is suitable and intended to protect at least the radiation output surface 27 from damaging environmental influences, for example, those caused by the ambient air. Such damaging environmental influences in the ambient air can include, for example, oxygen, ozone, acid rain, sulfur and sulfur compounds, as well as nitrogen oxides and hydrocarbons and other harmful chemicals. Such substances may also unintentionally penetrate a housing 1 sealed with a housing cover 14, since, due to the different coefficients of thermal expansion between copper and steel, there is a particular technical challenge in connecting and welding a steel-based housing cover 14 sufficiently tightly to the housing part 10.Particularly in high-volume production of such housings 1, an increase in the undetected proportion of components exhibiting residual leakage may occur. Therefore, the crystalline protective layer 6 may be necessary for the reliable operation of the laser diode chip 2 in a highly thermally conductive housing 1 described here, as additional protection at least for the radiation output area 27.

[0098] In particular, the crystalline protective layers 6 described below can be hermetically sealed and thus exhibit a sufficiently high degree of sealing to adequately protect the laser diode chip 2 throughout its entire lifetime. The crystalline protective layers 6 according to the following embodiments can be applied to the laser diode chip 2, for example, by means of an atomic layer deposition process, in particular by means of an atomic layer epitaxy process, or by means of a chemical vapor deposition process, particularly at temperatures greater than or equal to 500°C and preferably greater than or equal to 600°C. Protective layers 6 applied in particular by means of atomic layer deposition advantageously form a crystal defect-free, so-called "pin hole"-free structure, which exhibits good adhesion to surfaces, high stability, good formability, and a low-stress structure.

[0099] Furthermore, the thick first solder layer 3 and, if applicable, the thick second solder layer 5 can result in an increased supply of solder below the laser diode chip 2. This can cause solder particles to migrate upwards towards the laser diode chip 2, and in particular towards the radiation output surface 27. These particles can then diffuse through a non-hermetically sealed faceted coating, potentially leading to leakage currents across the radiation output surface 27. The crystalline protective layer 6 can thus also provide protection against the diffusion of solder to the surface of the laser diode chip 2. Furthermore, in the case of a dielectric material, the crystalline protective layer can significantly increase the breakdown field strength.

[0100] In Fig. Figure 10 shows an embodiment of a laser diode chip 2 in a sectional view, in which a crystalline protective layer 6 is applied directly to the radiation output surface 27 of the laser diode chip 2. The crystalline protective layer 6 comprises a dielectric material, for example, one of the dielectric materials mentioned above in the general section. Alternatively, it is also possible to arrange a dielectric passivation layer between the crystalline protective layer 6 and the radiation output surface 27, so that a semiconducting or conductive material, as described above in the general section, can also be used for the crystalline protective layer 6.

[0101] Furthermore, optical layers 7 in the form of layer stacks are applied to the radiation output coupling surface 27 and to the back surface 28 opposite the radiation output coupling surface 27. These layers are designed as anti-reflective or reflective coatings for the respective laser facet. For example, the optical layer 7 applied to the radiation output coupling surface 27 can be designed as an anti-reflective layer, while the optical layer 7 applied to the back surface 28 can be designed as a reflective layer. The optical layers 7 can be applied using a method commonly used for coating laser diode facets, which typically produces amorphous or semi-crystalline layers.

[0102] In the illustrated embodiment, the crystalline protective layer 6 is thus arranged between the optical layer 7 and the radiation output surface 27. To protect the radiation output surface 27, it may be sufficient for the crystalline protective layer 6 to have a thickness of a few nanometers up to a few tens of nanometers, so that the crystalline protective layer 6 has no influence on the optical properties of the coating applied to the radiation output surface 27, which are then essentially determined by the optical layer 7. Alternatively, it is also possible for the crystalline protective layer 6 to be formed as part of the optical layer 7 and to have a correspondingly selected thickness.

[0103] In Fig. Figure 11 shows an embodiment in which, in addition to the crystalline protective layer 6 on the radiation output surface 27, a crystalline protective layer 6 is also arranged on the back surface 28 between the back surface 28 and the optical layer 7. This allows the back surface 28 to be protected from both damaging gases and solder that may migrate or diffuse onto the back surface 28.

[0104] In Fig. Figure 12 shows a further embodiment in which the optical layer 7 on the radiation output coupling surface 27 is formed by the crystalline protective layer 6. For this purpose, the crystalline protective layer 6 has one and preferably several layers of different materials that exhibit the desired anti-reflective or reflective properties.

[0105] In Fig. Figure 13 shows a further embodiment in which the optical layer 7 on the back surface 28 is also formed by a crystalline protective layer 6. In this case as well, the crystalline protective layers 6 can each have one and preferably several crystalline layers made of different materials, which result in the desired anti-reflective or reflective properties.

[0106] In Fig. Figure 14 shows a further embodiment in which, in comparison to the embodiment of the Fig. 10. On the radiation output surface 27, the crystalline protective layer 6 is applied to the optical layer 7, such that the optical layer 7 is positioned between the crystalline protective layer 6 and the radiation output surface 27 and is thus covered by the crystalline protective layer 6. This allows the optical layer 7 to be protected by the crystalline protective layer 6 in addition to the radiation output surface 27. Furthermore, it is also possible to use a semiconducting material or a conductive material, for example one of the materials mentioned above in the general section, as an alternative to a dielectric material for the crystalline protective layer 6.

[0107] In the exemplary embodiment of the Fig. 15 a crystalline protective layer 6 is also applied to the optical layer 7 on the back surface 28, which can protect the back surface 28 as well as the optical layer 7 on the back surface 28.

[0108] In Fig. Figure 16 shows a further embodiment, which depicts the laser diode chip 2 in a top view and in which, in addition to the crystalline protective layer 6 on the radiation output surface 27 and the back surface 28, a crystalline protective layer 6 is applied to the side surfaces 29, connecting the back surface 28 and the radiation output surface 27. This provides all-around protection of the laser diode chip 2, and in particular its semiconductor layers and the interfaces between the semiconductor layers, since all side surfaces of the laser diode chip 2 are covered with the crystalline protective layer 6. The crystalline protective layer 6 can be applied as shown in Figure 16. Fig. Figure 16 shows that the crystalline protective layer 6 is applied over the optical layers 7. Alternatively, it is also possible to apply the crystalline protective layer 6 directly to the radiation output coupling surface and / or the back surface 28.

[0109] The features shown and described in the figures and exemplary embodiments can be combined with one another according to further exemplary embodiments, even if such combinations are not explicitly shown in the figures. In particular, the different housing shapes, the use of a thermal interface element 4, and the arrangement of one or more protective layers 6 on the laser diode chip 2 can be combined with one another. Furthermore, the exemplary embodiments shown in the figures can also have alternative or additional features according to the embodiments described in the general part.

Claims

[1] Laser diode device, comprising a housing (1) with a housing part (10) and with a mounting part (11) connected to the housing part (10) and extending away from the housing part (10) along an extension direction (110), and a laser diode chip (2) on the mounting part (11), which has semiconductor layers (21, 22, 23, 24, 26) with an active layer (23) for emitting light on a substrate (20), where the housing part (10) and the mounting part (11) have a base body made of copper and at least the housing part (10) is steel-coated, a first solder layer (3) is arranged between the laser diode chip (2) and the mounting part (11), which first solder layer has a thickness of greater than or equal to 3 µm, the laser diode chip (2) is based on a nitride compound semiconductor material and has a non-polar or semi-polar crystal structure, and the first solder layer (3) comprises an indium-based soft solder. [2] Laser diode device according to the preceding claim, wherein the active layer (23) has an area of ​​greater than or equal to 10000 µm 2 has. [3] Laser diode device according to one of the preceding claims, wherein the thickness of the first solder layer (3) is greater than or equal to 5 µm. [4] Laser diode device according to one of the preceding claims, wherein a heat conducting element (4) is arranged between the laser diode chip (2) and the mounting part (11). [5] Laser diode device according to claim 4, wherein the heat conducting element (4) is fixed to the mounting part (11) with the first solder layer (3) and the laser diode chip (2) is fixed to the heat conducting element (4) with a second solder layer (5) having a thickness of greater than or equal to 3 µm. [6] Laser diode device according to claim 4 or 5, wherein the heat conducting element (4) comprises SiC, BN, CuW or diamond. [7] Laser diode device according to one of the preceding claims, wherein a housing cover (14) is applied to the housing part (10) and welded to the housing part (10) and the mounting part (11) projects along the extension direction (110) from the housing part (10) into the housing cover (14). [8] Laser diode device according to claim 7, wherein the mounting part (11) projects perpendicular to the extension direction (110) at least on one side up to the housing cover (14). [9] Laser diode device according to claim 7 or 8, wherein the housing part (10) and the housing cover (14) have a circular cross-section in a plane perpendicular to the extension direction (110) and the mounting part (11) has a cross-section in a plane perpendicular to the extension direction (110) which occupies more than a semicircular area. [10] Laser diode device according to one of the preceding claims, wherein the mounting part (11) has a cross-section which increases in the direction of the housing part (10). [11] Laser diode device according to claim 10, wherein the mounting part (11) has a wedge-shaped cross-section in a plane parallel to the extension direction (110). [12] Laser diode device according to claim 11, wherein the housing part (10) has a wedge-shaped cross-section in a plane parallel to the extension direction (110). [13] Laser diode device according to one of the preceding claims, wherein the laser diode chip (2) has a radiation coupling-out surface (27) on which a crystalline protective layer (6) is applied.

Images