TWI511396B - Laser diode assembly - Google Patents

Description

Laser diode assembly

A laser diode assembly is specifically described.

The present patent application claims priority to German Patent Application No. 10 2012 102 305.0, the entire disclosure of which is incorporated herein by reference.

Light sources with high optical power densities are key components for many applications. For example, a laser diode composed of a nitride-based compound semiconductor material system has a high market potential in projection systems, particularly those having a luminous flux of 1000 to 10,000 lumens.

Therefore, parts with high output power and miniaturized housing are required for such applications. Based on cost and in the context of standardization, housings of the so-called TO-type sequence (TO: "transistor profile") in the form of TO metal housings ("TO metal cans") often have, for example, conventional structural dimensions TO38, TO56 and In the form of TO90, wherein the TO metal housing is substantially made of steel. However, to date, commercially available laser diodes (also referred to simply as "TO housings") designed according to standard TO are limited to optical powers below 3 watts, which is insufficient for many applications. However, optical powers of more than 3 watts have not been achieved with this design to date.

For example, C. Vierheilig et al., Proc. SPIE, vol. 8277, 82770K, 2012, discloses several blue-nitride-based laser diodes in a TO housing that operate at a continuous wave at room temperature. Light between 440 nm and 460 nm and output power of up to 2.5 watts.

It has often been attempted to increase the optical output power by increasing the size of the optical resonator (i.e., especially the wafer area), since nitride-based laser diodes have been found to have long-term aging properties depending on current density, such as S. Lutgen et al. are described in the literature Proc. SPIE, vol. 7 953, page 79530 G1-12, 2011. In addition, the addition of the active region also makes it possible to improve the heat transfer from the light generating layer in the direction of the heat sink.

However, the inventors of the present application have found in their own experiments and studies that increasing the wafer area does not result in an increase in power. In this regard, FIG. 1A illustrates the measurement of the optical output power P (in watts) of the blue-emitting laser diode wafer based on the nitride compound semiconductor material with the operating current I (unit ampere) as the horizontal axis. In this case, the laser diode chips used for measurement are each located in the TO housing. Measurement curves 1001 and 1002 for two individual wafers each having a part size of 200 micrometers by 1200 micrometers and an active region of 15 micrometers by 1200 micrometers were measured. In order to achieve higher power, the above method for doubling the wafer area was tested. The power that is expected to increase is doubled in the form of a dashed line 1003. However, it has been found that, contrary to expectations, the maximum power achievable by doubling the wafer area is even smaller than in the case of individual wafers, which can be compared with the individual wafers described above using a curve 1004 of a laser diode with a double active region. understand.

In addition to the standard TO housing consisting of high-grade steel, in order to have a better heat dissipation, it is known to have a TO housing which is based on copper or has a shell portion of a copper core and a steel surface, as described in the document DE 1184870. It is intended to improve the heat dissipation of the laser diode wafer because of its good thermal conductivity.

1B is based on the experiment of the present inventors, using the operating current I (unit amps) as the horizontal axis to illustrate the optical output power P (in watts) of the laser diode wafer and the operating voltage U (in volts) in different TO housings. Measured value. Curves 1005 and 1007 illustrate the current-dependent optical power and correlation of a blue-emitting gallium nitride laser diode in a conventional TO56 standard housing having a steel substrate ("backplane") and a copper mounting portion ("handle"). The operating voltage, while curves 1006 and 1008, illustrate the corresponding measurements of the laser diode wafer in a replacement TO56 housing with a steel-sheathed copper base and a copper-clad copper mounting. It is easy to see that an alternative housing with a copper-clad copper substrate cannot directly improve the maximum power of the laser diode wafer. Therefore, any laser diode manufacturer no longer pursues an alternative TO housing for a nitride-based laser diode.

At least one object of a particular embodiment is to specify a laser diode assembly.

This goal is achieved with a separate entry for the scope of the patent application. Advantageous embodiments and developments of the individual items are described in the dependent items and are also apparent from the following description and the accompanying drawings.

In accordance with at least one embodiment, a laser diode assembly includes a housing in which a laser diode wafer is disposed. especially, The housing has a housing portion and a mounting portion coupled to the housing portion and extending away from the housing portion along an extension direction. In other words, the mounting portion protrudes away from the housing portion and can be embodied as a pin-type fashion, for example. The mounting portion has a mounting region extending away from the housing portion along the extending direction of the mounting portion and the laser diode chip disposed thereon. In particular, the housing portion can be mounted and designed such that it is possible to arrange a housing cover on the housing portion for closing the housing.

The casing portion and the mounting portion (in particular, it may be embodied in an integrated manner) each have a body made of copper or the like, and in the specific embodiment, there is a common body made of copper. Furthermore, at least the housing portion is covered by steel. This means that the housing portion is substantially formed of copper of the body and covered by steel. For example, the steel layer can be formed from a layer composed of high grade steel.

Furthermore, the housing portion may have a hole or opening, for example, an electrical lead, for example in the form of a contact foot, through which the housing portion may protrude away from one side of the mounting portion to the configuration. One side of the department. Electrical leads that are in electrical contact with the laser diode chip can be mounted, for example, via electrical leads to the wires of the laser diode wafer.

According to another specific embodiment, the mounting portion is also covered by steel in addition to the housing portion. In particular, in this embodiment, the housing portion and the mounting portion may have a common copper body covered by steel.

In particular, the housing can be embodied as a so-called TO housing having, for example, a structural dimension TO38, TO56 or TO90. The housing portion may also be referred to as a "bottom plate" and the mounting portion is referred to as a "shank." At least a housing portion or a housing portion that is conventionally used and that is substantially composed of steel without a copper-based body and Compared to the standard TO housing of the mounting portion, the housing described herein has a higher thermal conductivity due to the copper in the steel-clad housing portion.

According to another specific embodiment, the housing has a housing cover that is laid over the housing portion and welded to the housing portion. For this purpose, it is particularly advantageous for the housing part to be covered by steel, so that in the case of a standard TO housing with a steel base, the housing cover can be welded to the housing part. The mounting portion protrudes from the housing portion into the housing cover along an extending direction, such that the laser diode wafer is formed by the housing cover and the housing portion in the case where the housing cover is mounted The cavity is located on the mounting portion. The housing cover also has a window on a side facing away from the housing portion through which light emitted by the laser diode wafer can be ejected from the laser diode assembly. The housing cover may comprise or consist of, for example, steel, in particular high-grade steel, in addition to the window. Since the housing portion is welded to the housing cover (which is embodied in the form of a cover above the mounting portion and also above the laser diode wafer on the mounting portion), it can be airtight or at least The housing is closed very tightly.

According to another embodiment, the laser diode chip is disposed on the mounting portion with a first solder layer. In particular, this means that the first solder layer is disposed between the laser diode wafer and the mounting portion. The first solder layer has a thickness greater than or equal to 2 microns. The thickness of the solder layer may also be preferably greater than or equal to 3 microns, and may also be greater than or equal to 5 microns.

The laser diode wafer can be directly mounted on the mounting portion with the first solder layer. Alternatively, a heat conduction element embodied as a so-called heat sink may be disposed between the laser diode wafer and the mounting portion. In particular, the thermally conductive element can be used to expand or diffuse the laser diode wafer with the The heat flow between the mounting portions enables a large transfer area, i.e., especially the mounting portion, during heat transfer into the housing. Furthermore, it is also possible that the thermally conductive element can compensate for, for example, the strain between the laser diode wafer and the housing, for example caused by their different coefficients of thermal expansion.

According to another embodiment, the thermally conductive element is secured to the mounting portion by the first solder layer. The laser diode wafer is secured to the thermally conductive element with a second solder layer. For example, the second solder layer may also have a thickness greater than or equal to 2 microns, preferably greater than or equal to 3 microns, and more preferably greater than or equal to 5 microns. The features and advantages associated with the first solder layer also apply to the second solder layer and vice versa.

According to another specific embodiment, the thermally conductive element comprises or consists of tantalum carbide (SiC), boron nitride (BN), copper tungsten alloy (CuW) or diamond. Tantalum carbide, boron nitride, copper-tungsten alloys and diamonds are characterized by a particularly high thermal conductivity. Alternatively, the thermally conductive element may also comprise aluminum nitride.

With regard to the laser diode assembly described herein, therefore, there may be one or more of the same different coefficients of thermal expansion between the body of the copper-based mounting portion, which often has different coefficients of thermal expansion, and the laser diode wafer. The material, in particular the first solder layer, furthermore, for example, a steel cover layer of the mounting portion and/or one or more other solder layers and/or thermally conductive elements. As a result, during operation, heat may be formed between the laser diode wafer and the housing or between the laser diode wafer and the thermally conductive element and also between the thermally conductive element and the housing. A thermally induced strain that adversely affects the operation of the laser diode assembly. Thickness of the solder layer commonly used in prior art to mount a laser diode wafer As thin as possible, especially below 2 microns, for optimum heat dissipation, as described for the laser diode assembly, which uses a much larger thickness of the preferred first solder layer, and if desired The second solder layer is also. The higher thermal resistance of this solder layer is accepted here because it can be demonstrated that this thick solder layer facilitates compensation for thermally induced strain between the housing and the laser diode wafer. For example, the solder layer described herein may comprise an indium based soft solder in order to be able to compensate for different thermal expansions particularly well. As far as the laser diode assembly is described, it is therefore possible to use a material such as tantalum carbide, boron nitride, copper tungsten alloy or diamond as the heat conductive element, which has higher thermal conductivity than aluminum nitride. Moreover, there are more distinct thermal expansion coefficients than the conventional materials of the laser diode wafer.

As also mentioned above, the application of a housing such as a TO housing, based on copper or a copper core and a steel surface, does not lead to an improvement in laser power, as compared to the application of a standard TO housing composed of high-grade steel. . In addition, the application of a solder layer having a thickness greater than or equal to 2 microns also appears to be counterproductive because of the higher thermal resistance. However, it has been found that with respect to the laser diode assembly described herein, it is possible to achieve multiple watts (especially, above 3 watts) due to the combination of the described housing and the thick first solder layer. The higher optical output power, as well as the electrical input power and optical output power, also have higher conversion efficiency.

According to another specific embodiment, the laser diode wafer is based on a nitride compound semiconductor material. In particular, the laser diode wafer may comprise a substrate, preferably a conductive substrate such as crystalline (indium, aluminum, gallium) nitrogen. An epitaxial layer sequence can be laid over it, that is, an epitaxial growth semiconductor The layer, which is based on a nitride compound semiconductor material, is thus based on indium aluminum gallium nitride (InAlGaN).

A compound semiconductor material based on indium aluminum gallium nitride, a compound semiconductor material based on (indium, aluminum, gallium) nitrogen, and a nitride compound semiconductor material system include, in particular, a III-V compound semiconductor material system In _x Al _y Ga _{1- Xy} N composed of materials, here 0 x 1,0 y 1, and x+y 1, that is, for example, gallium nitride, aluminum nitride, aluminum gallium nitride, indium gallium nitride, aluminum indium gallium nitride. In particular, the laser diode wafer has a semiconductor layer sequence on the substrate with an active layer for illuminating during operation, based on aluminum gallium indium nitride (AlGaInN) and/or indium gallium nitride (InGaN). good. In particular, the laser diode wafer can emit light from the ultraviolet to green wavelength range during operation.

In accordance with another embodiment, the laser diode wafer has a semiconductor layer on the substrate, such as an active layer between the waveguide layer and the cladding layer. In particular, it is possible to lay a first cladding layer on the substrate, a first waveguide layer thereon, an active layer thereon, a second waveguide layer thereon and a second cladding layer thereon . Above the second cladding layer, it is also possible to arrange a semiconductor contact layer and an electrical connection layer thereon, for example in the form of a metal layer. It is particularly preferred to establish electrical contact of the laser diode wafer via an electrical connection layer located opposite the substrate and also via the conductive substrate, wherein the substrate can also be electrically connected on a side facing away from the semiconductor layers. Floor. On the side of the active layer facing away from the substrate, a charge carrier barrier layer may also be disposed between the waveguide layer and the cladding layer to avoid a so-called charge carrier overshoot.

For example, a semiconductor layer disposed between the substrate and the active layer may be doped n-type, and a semiconductor layer (viewed from the substrate) may be p-type doped disposed above the active layer. Alternatively, the order of doping may also be reversed. The active layer may be doped without doping or n-type. The laser diode wafer may have, for example, a conventional pn junction, a double heterostructure or a quantum well structure as an active layer, and a multiple quantum well structure (MQW structure) is particularly preferred. In the context of this application, in particular, the name quantum well structure encompasses any structure in which the charge carriers are quantized by the limitation of the empirical energy state. In particular, quantum well structures can have quantum wells, quantum wires, and/or quantum dots and combinations of such structures. For example, the active layer may have an indium gallium nitride based quantum film between appropriately defined barrier layers.

In accordance with another embodiment, the laser diode wafer has a radiation coupling-out area through which light generated in the active layer is radiated. It is preferred to embody the laser diode wafer as a side-emitting laser diode wafer, wherein the semiconductor layer composite assemblage is broken, cleaved, and/or etched, for example, along the crystal plane. The radiation coupling out zone can be generated. In addition, the laser diode wafer has a rear side region disposed opposite the radiation coupling region. In particular, the area in the front side region of the laser diode wafer through which the same dimming light generated in the laser diode wafer is radiated may be referred to as a radiation coupling-out region. In the case of edge-emitting laser diode wafers, the front side regions, in particular the radiation coupling-out regions, and the rear side regions are also often referred to as so-called facets. In addition, the laser diode chip has a side region interconnecting the rear side region and the radiation coupling region, and the side regions are formed by the semiconductor layer and the semiconductor layer The side faces are formed in the direction in which the direction is perpendicular.

According to another embodiment, the laser diode wafer has a crystal protective layer at least on the radiation coupling region. Here and below, a "crystalline" layer refers to a layer having a crystal structure as a whole (i.e., a short-range and a long-range order). Conversely, the amorphous layer has only short-range regularity and some of the crystalline or partially crystalline layers also have short-range regularity in parts or regions, but the entire layer has no continuous long-range regularity.

In particular, the crystal protective layer may be hermetically impermeable, particularly in the region of the radiation coupling region, that is, preferably in the front side region of the laser diode wafer. The area through which radiation is radiated during operation. In this case, in particular, the hermetic barrier layer may have sufficient to protect the hermetically impermeable layer in the laser diode wafer during the lifetime of the laser diode wafer and the laser diode assembly. The impermeability of the covered area is such that damage that shortens the service life does not occur. In particular, the crystal protective layer may have a barrier property higher than, for example, an amorphous or partially crystalline layer. For example, this can be based on the fact that the crystalline layer is preferably embodied as a lattice defect that does not have a so-called "pinhole" which may cause leakage.

The crystal protective layer protects the area of the laser diode wafer covered by the crystal protective layer, that is, at least the radiation coupling-out area, from environmental influences such as harmful gases. Such environmental effects can be caused, for example, by oxygen, ozone, substances in acid rain, and other chemicals. For example, when a laser diode assembly is used as a light source for automotive engineering, in the case where the laser diode wafer is unprotected, it may be corroded by a medium (eg, hydrocarbons and sulfur and nitrogen compounds such as hydrogen sulfide). And sulfur and nitrogen oxides) and endanger the laser diode The body wafer, especially its radiation coupling-out area. Such harmful environmental influences can penetrate the housing of the laser diode assembly as far as the laser diode wafer, for example when the housing itself is not hermetically sealed against airtightness. In the case of the housing of the laser diode assembly described herein, due to the difference in thermal expansion coefficient, when the sealing of the closed casing, the copper- or copper-clad-clad casing and the steel-based casing cover is sufficiently impervious There are special technical challenges. In particular, when mass-producing such parts, the escape rate of parts with residual leakage may increase. Although it is known to have a facet of a laser diode wafer, the coating is often amorphous to partially crystalline, and because of the gray borders and imperfections, it prevents damage to the faceted material only to spread. To an inadequate extent. Thus, the crystal protective layer constitutes an additional protection, in particular a critical radiation coupling-out region, which ensures reliable use of the laser diode assembly.

Furthermore, the thick solder layer (eg, the first solder layer) described herein between the laser diode wafer and the housing may have the following effect: surface migration of solder particles via the laser diode wafer Especially in the area of the laser faceted. In the absence of sufficient anti-seepage of the facet coating, the solder particles may diffuse through the facet coating, which may result in leakage current through the laser facet. The crystal protective layer described herein ensures a sufficiently impervious facet coating to prevent damage to the laser diode wafer caused by the solder particles. With the crystal protective layer, it is again possible to achieve a large increase in breakdown field strength in the case of a crystalline dielectric material, whereby it is possible to achieve protection against, for example, solder layer upflow or p-type metallization. Electrical breakdown caused above the facet.

In particular, in a particularly advantageous embodiment, The laser diode assembly includes the copper-based housing and the laser diode wafer, wherein the first solder layer having a thickness greater than or equal to 2 micrometers is disposed on the laser diode wafer and the mounting portion And wherein the laser diode wafer has a radiation coupling-out region, and the radiation coupling-out region is provided with a crystal protective layer. Due to the combination of these features (eg, in the case of thick solder layers, which is inconsistent with improved heat removal), the laser diode assembly can still improve heat dissipation for higher output power. As a result, with the low strain of the laser diode chip, the excellent heat transfer of the laser diode chip, and the optimum combination of high part reliability, it is possible to ensure a large increase in the light output power.

In accordance with another embodiment, the laser diode wafer is provided with a crystal protective layer at least over the radiation coupling region during production of the laser diode assembly. For this purpose, an application method capable of producing a crystalline dielectric, semiconductor or conductive layer is used. For example, it is possible to select a chemical vapor deposition (CVD) method in which the temperature is increased, particularly a temperature greater than or equal to 500 ° C, and preferably greater than or equal to 600 ° C. The crystal protective layer can also be deposited by atomic layer deposition (ALD), in particular, atomic layer epitaxy (ALE). The atomic layer deposition method may also be carried out at a temperature higher than or equal to 500 ° C as compared with the conventional method for producing a facet coating, and it is preferable to obtain a crystal protective layer of 600 ° C or more. The above methods (in particular, atomic layer deposition) have the advantages of defect-free, "pinhole-free" structure, excellent surface adhesion, high stability, excellent overforming, and unevenness in high aspect ratio. Degree, as well as low strain structure. In the case of such a protective layer, it is particularly advantageous to have low permeability to gases, for example, oxygen or humid air, such as P.F. Carcia et al. It is described in Journal of Applied Physics 106, 023533 (2009) and T. Hirvikorpia in the article Applied Surface Science 257, 9451-9454 (2011).

According to another embodiment, the crystal protective layer has only one crystalline layer. Alternatively, it is also possible for the crystal protective layer to have a plurality of crystalline layers. The plurality of crystal layers may be formed, for example, from a plurality of crystal layers composed of different materials. Furthermore, it is also possible that at least two crystal layers composed of different materials form the plurality of crystal layers in an alternating sequence.

According to another specific embodiment, an optical layer is laid over the radiation coupling region. The optical layer, for example, can be a reflective or anti-reflective layer. Such optical layers often have a layer of a transparent material (preferably a plurality of layers), and a plurality of layers of a transparent material to form a periodic sequence of different refractive indices.

For example, the crystal protective layer can form the optical layer. This may be advantageous, especially when the crystal protective layer has a plurality of crystalline layers. Alternatively, in addition to the crystal protective layer, it is also possible to lay an optical layer, which is not necessarily a crystalline layer, but may, for example, be an amorphous or partially crystalline layer. In this case, the optical layer can be laid by conventional laying methods, such as those used in the prior art for faceted coatings.

The optical layer can be disposed between the radiation coupling region and the crystal protective layer, for example, and can be covered with the crystal protective layer. This makes it possible to protect the optical layer with the crystal protective layer in addition to the radiation coupling-out region. Alternatively, it is also possible to configure the crystal protection layer between the radiation coupling region and the optical layer. In this case, as close as possible to the laser II It is advantageous to arrange the crystal protective layer on the polar body wafer, and it is particularly preferred to be directly disposed on the laser diode wafer, that is, at least on the radiation coupling-out region. In combination with another optical layer, the crystal protective layer may also have a portion of the optical function of the coating to be part of the optical layer.

According to another specific embodiment, the crystal protective layer is formed of a dielectric material or at least comprises a dielectric material. In particular, the dielectric layer is advantageous in terms of a direct coating of the radiation coupling region and, if appropriate, other regions of the laser diode wafer, since a short circuit of the laser diode wafer can be avoided thereby. The crystal protective layer may also comprise or consist of a semiconductor or conductive material in combination with a crystal protective layer, an optical layer or a passivation layer between the laser diode wafers.

It is particularly preferred that the crystal protective layer is formed of an oxide or at least an oxide. Since the oxygen of the oxide material forms a hydrogen bridge bond with the water molecules, for example, water molecules can be prevented from penetrating into the crystal layer. The oxide is particularly preferred as a dielectric.

The crystal protective layer may comprise one or more of the following materials in one or more of the crystalline layers: Al ₂ O ₃ , Si ₃ N ₄ , Nb _x Al _y O _z , Al ₂ O ₃ /TiO ₂ , Al ₂ O ₃ /Ta ₂ O ₅ , HfO ₂ , Ta ₂ O ₅ /ZrO ₂ , Ta ₂ O ₅ , Ta _x Ti _y O _z , Ta ₂ O ₅ /NbO ₅ , TiO ₂ , ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , Sc ₂ O ₃ , Y ₂ O ₃ , MgO, B ₂ O ₃ , SiO ₂ , GeO ₂ , La ₂ O ₃ , CeO ₂ , PrO _x , Nd ₂ O ₃ , Sm ₂ O ₃ , EuO _x , Gd ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , Lu ₂ O ₃ , SrTiO ₂ , BaTiO ₃ , PbTiO ₃ , PbZrO ₃ , Bi _x Ti _y O, Bi _x Si _y O, SrTa ₂ O ₆ , SrBi ₂ Ta ₂ O ₉ , YScO ₃ , LaAlO ₃ , NdAlO ₃ , GdScO ₃ , LaScO ₃ , LaLuO ₃ , Er ₃ Ga ₅ O ₁₃ , HfSiO, HfTiO, AlSiO, LaAlO, LaHfO, In ₂ O ₃ , ZnO, Ga ₂ O ₃ , V ₂ O ₅ , HfAlO, HfTaO, HfZrO, Ru, Pt, Ir, Td, Rh, Ag, W , Cu, Co, Fe, Ni, Mo, Ta, Ti, Al, Si, Ge, In ₂ O ₃ , In ₂ O ₃ :Sn, In ₂ O ₃ :F, In ₂ O ₃ :Zr, SnO ₂ , SnO ₂ : Sb, ZnO: Al, ZnO: B, ZnO: Ga, RuO ₂ , RhO ₂ , IrO ₂ , Ga ₂ O ₃ , V ₂ O ₅ , WO ₃ , W ₂ O ₃ , BN, AlN, GaN, InN, SiN _x , Ta ₃ N ₅ , Cu ₃ N, Zr ₃ N ₄ , Hf ₃ N ₄ , NiO, CuO, FeO _x , CrO _x , CoO _x , MnO _x TiN, Ti _x Si _y N _z , NbN, TaN, Ta ₃ N ₅ , MoN _x , W ₂ N, GaAs, AlAs, AlP, InP, GaP, InAs, TaC.

According to another embodiment, a crystal protective layer is also laid over the back side region of the laser diode wafer opposite the radiation coupling region. The use of a crystal protective layer on the radiation coupling region and the back side region can effectively protect the facet of the laser diode that is sensitive to environmental influences.

Furthermore, an optical layer, in particular a reflective layer, can be laid on the rear side region. As described above in describing the coating of the radiation coupling region, it is also possible to lay an optical layer between the crystal protective layer and the rear side region on the rear side region. Alternatively, the crystal protective layer may be disposed between the optical layer and the rear side region. It is also particularly advantageous if the optical layer on the side regions behind the laser diode wafer is formed by a crystalline protective layer.

According to another embodiment, one or more layers of a crystalline protective layer are laid over the side regions of the laser diode wafer that connect the backside regions to the radiation coupling regions. In particular, if the crystal protective layer is laid on all side regions perpendicular to the growth and arrangement direction of the semiconductor layer and on the facet of the laser diode wafer, the interface between the semiconductor layer and the semiconductor layer is Comprehensive protection is beneficial.

1‧‧‧shell

2‧‧‧Laser Diode Wafer

3‧‧‧First solder layer

4‧‧‧thermal element

5‧‧‧Second solder layer

6‧‧‧ crystal protective layer

7‧‧‧Optical layer

10‧‧‧Shell Department

11‧‧‧Installation Department

12‧‧‧ steel cover

13‧‧‧Installation area

14‧‧‧Shell cover

15‧‧‧ window

20‧‧‧Substrate

21‧‧‧coating

22‧‧‧Wave layer

23‧‧‧Active layer

24‧‧‧Semiconductor contact layer

25‧‧‧Electrical connection layer

27‧‧‧radiation coupling area

28‧‧‧ Back side area

29‧‧‧ Side area

100 to 104‧‧‧Laser diode components

110‧‧‧ Direction

401 to 404‧‧‧ Curve

1001, 1002‧‧‧Measurement curve

1003‧‧‧dotted line

1004 to 1008‧‧‧ curve

Other advantages, advantageous embodiments, and developments will be apparent from the exemplary embodiments described herein.

1A and 1B illustrate measured values of the properties of a conventional laser diode assembly, and FIGS. 2A and 2B schematically illustrate a laser diode assembly according to an exemplary embodiment, FIG. The schematic diagram shows a laser diode wafer according to an exemplary embodiment, and FIG. 4 illustrates measured values of the properties of the laser diode assembly, and FIGS. 5A to 5G are schematic diagrams according to other exemplary embodiments. The components of the laser diode assembly, and Figures 6 through 7C, schematically illustrate a laser diode assembly in accordance with other exemplary embodiments.

In the exemplary embodiments and the drawings, elements of the same or the same type are denoted by the same element symbols in each case. The illustrated elements and their dimensional relationships are not to be drawn to true scale; instead, the dimensions of the individual elements (eg, layers, structural parts, parts, and regions) may be shown in an exaggerated manner for better mapping. Explain and / or provide a better understanding.

2A and 2B illustrate an exemplary embodiment of a laser diode assembly 100, wherein FIG. 2A is a schematic cross-sectional view and FIG. 2B The plan view illustrates the front side of the laser diode assembly 100 opposite the direction 110 in FIG. 2A. The following description also relates to FIG. 2A and FIG. 2B.

The laser diode assembly 100 comprises a housing 1 embodied in the form of a so-called TO housing. The casing 1 has a casing portion 10 and a mounting portion 11 disposed on the casing portion. In the illustrated exemplary embodiment, the mounting portion 11 extends away from the housing portion 10 along the direction of extension 110 and is embodied in a manner that is integral with the housing portion 10. For this purpose, the housing portion 10 and the mounting portion 11 have a body formed of copper. The housing portion 10 also has a cover layer 12 of steel formed by a coating of a copper body in the region of the housing portion 10.

Further, the housing portion 10 may have a hole or an opening, for example, in which a small leg portion projecting from the side of the housing portion 10 away from the side of the mounting portion 11 to the side of the mounting portion 11 is disposed. For example, the configuration and the small pins that are fixed therein can be embodied as electrical feedthroughs, as well as providing the possibility of establishing electrical contacts.

The mounting portion 11 has a mounting area 13 on which the laser diode 2 is placed. In particular, the laser diode 2 is mounted on the mounting region 13 of the mounting portion 11 with the first solder layer 3 to be electrically and thermally connected to the housing 1.

The housing cover 14 is configurable above the mounting portion 11 and above the laser diode wafer 2, the housing cover being indicated by dashed lines. For example, the housing cover 14 of the window 15 may also comprise steel and, in addition to the window 15, is preferably constructed of steel. Since the housing portion 10 has a steel cover 12, the housing cover 14 can be laid on the housing portion 10 of the housing 1, as well as a conventional TO housing such as a steel substrate, which can be fixed by welding in a standard process.

Although it is common to optimize the dissipation of the standard laser diode parts by coupling the laser diode wafer to the housing via the thinnest possible solder layer, in order to obtain as low a thermal resistance as possible, The first solder layer 3 in the embodiment has a thickness greater than or equal to 2 μm, preferably greater than or equal to 3 μm, and particularly preferably greater than or equal to 5 μm. Thereby, it is possible to compensate for heat-induced stress which occurs during operation due to heat generated by the laser wafer 2 and different thermal expansion coefficients of the laser diode 2 and the casing 1. Further, for example, the surface of the mounting portion 13 of the mounting portion 11 can be compensated for unevenness by using such a thick solder layer. In particular, as shown in Fig. 6, if the mounting portion 11 has a cover layer 12 made of steel like the casing portion 10, unevenness may occur.

As shown in FIG. 3, the laser diode chip 2 is formed to have a radiation-coupled-out region 27 formed by a side region and a side-emitting laser diode wafer located at a side region 28 opposite to the radiation-coupled region. good. In particular, the radiation coupling-out region 27 can be formed by the front side region of the laser diode wafer 2, during which the laser radiation generated by the laser diode wafer 2 is emitted through the front side region.

In particular, the laser diode 2 is a nitride compound-based semiconductor material. For this purpose, the laser diode chip 2 has a substrate 20 which is preferably embodied as a conductive type and which comprises, for example, crystalline (indium, aluminum, gallium) nitrogen or of the same. It is preferable to use an epitaxial method such as metal organic vapor phase epitaxy (MOVPE) to grow a semiconductor layer sequence based on a nitride compound semiconductor material. The laser diode chip 2 has an active layer 23 disposed between the waveguide layer 22 and the cladding layer 21 on the substrate 20. In particular, the laser diode The bulk wafer 2 has a first cladding layer 21 on the substrate 20, a first waveguide layer 22 on the first cladding layer, and an active layer 23 on the first waveguide layer 22. Along the growth direction, there is another waveguide layer 22 and another cladding layer 21 and semiconductor contact layer 24 on top of the active layer 23, and the semiconductor contact layer 24 is in contact with an electrical connection layer 25, for example in the form of a metal electrode layer. The laser diode 2 is electrically connected to the conductive substrate 20 via the electrical connection layer 25, and the conductive substrate 20 may have another electrical connection layer on one side facing away from the semiconductor layers 21, 22, 23 and 24. Show).

In the exemplary embodiment shown by the active layer 23, the semiconductor layers facing the substrate 20 are all n-type doped, and the semiconductor layers disposed on one side of the active layer 23 facing away from the substrate 20 are all p-doped. . Alternatively, the opposite doping sequence is also possible. The active layer 23 can be n-type doped or undoped, for example, and can have multiple quantum well structures, particularly, in the exemplary embodiment illustrated.

In particular, the copper-based housing 1 achieves improved thermal conductivity compared to a standard TO housing composed of steel. In Fig. 4, in this respect, in each case, the operating current I (unit ampere) is plotted on the horizontal axis, the curves 401 and 402 are illustrated as the light output power P (in watts), and the curves 403 and 404 are plotted. The operating voltage U (in volts) of a blue gallium nitride based laser diode wafer, in which a laser diode wafer is tested in a standard TO56 housing having a steel substrate, and is described herein. Steel copper constitutes a laser diode wafer in a copper-based casing of a casing portion to which a solder layer having a thickness of about 5 μm is attached. Comparing the curves 401 and 403 for the case of the copper-based case and the thick solder layer described herein, and the case for the standard TO case and the thin solder layer Curves 402 and 404 show that although the thicker solder has a higher thermal resistance, the use of a housing having the description of the first solder layer 3 described herein can improve the output power.

According to other exemplary embodiments, the laser diode chip 2 has a crystal protective layer 6 on at least the radiation outcoupling region 27, as illustrated below to illustrate the fifth embodiment of the exemplary embodiment of the laser diode wafer 2. As shown in FIG. 5G, the laser diode 2 can be incorporated into the housing 1 of the laser diode assembly described herein with a partially illustrated solder layer. For the sake of brevity, the subsequent figures do not illustrate the layer structure of the laser diode wafer 2.

The laser diode chip 2 of the following exemplary embodiment has a crystal protective layer 6 at least on the radiation coupling-out region 27, which is suitable and arranged to at least protect the radiation coupling-out region 27 from harmful environmental influences, for example Caused by the surrounding air. Harmful environmental effects of the surrounding air, for example, may be oxygen, ozone, acid rain, sulfur and sulfur compounds and nitrogen oxides and hydrocarbons, and other harmful chemicals. It is also possible for such a substance to inadvertently penetrate into the casing 1 sealed by the casing cover 14 because the steel-based casing cover 14 and the casing portion 10 are sufficiently imperviously connected due to the different thermal expansion coefficients of copper and steel. It is a special technical challenge. In particular, when the casing 1 is mass-produced, an unidentified ratio of parts having residual leakage may increase. Therefore, in order to reliably use the laser diode wafer 2 described in the housing 1 having high thermal conductivity, a crystal protective layer 6 as an additional protection for at least the radiation coupling-out region 27 may be required.

In particular, the crystal protective layer 6 described below can be hermetically barrier-proof so as to be sufficiently high to adequately protect the mine throughout its useful life. The barrier property of the diode chip 2 is obtained. The crystal protective layer 6 according to the following exemplary embodiment is laid on the laser diode 2, for example, by atomic layer deposition, in particular atomic layer epitaxy, or chemical vapor deposition, especially at 500 ° C or higher. The temperature is preferably greater than or equal to 600 ° C. In particular, the protective layer 6 laid by atomic layer deposition advantageously forms a so-called "pinhole-free" structure free of crystal defects, which has excellent surface adhesion, high stability, excellent superformability, and low strain structure.

In addition, due to the thick first solder layer 3, and if appropriate, also due to the thick second solder layer 5, as explained below in the description of Figures 7A to 7C, the laser can be added The solder supply under the polar body wafer 2 has the effect that the solder particles can migrate upward to the laser diode wafer 2 (in particular, the radiation coupling-out region 27) and the face coating that can diffuse through the non-hermetic barrier. Layer, which may result in leakage current through the radiation coupling out region 27. Therefore, the use of the crystal protective layer 6 also protects the solder from diffusing to the surface of the laser diode wafer 2. Furthermore, in the case of dielectric materials, the crystal protective layer 6 can cause a significant increase in the strength of the collapse field.

The cross-section of Figure 5A illustrates an exemplary embodiment of a laser diode 2 in which the crystal protective layer 6 is applied directly to the radiation coupling region 27 of the laser diode wafer 2. For this purpose, the crystal protective layer 6 comprises a dielectric material such as one of the dielectric materials mentioned above in the general part. Alternatively, it is also possible to configure a dielectric passivation layer between the crystal protective layer 6 and the radiation coupling-out region 27 such that a semiconductor or conductive material as mentioned in the general portion can also be used for the crystal protective layer 6.

In addition, the optical layer 7 in the form of a layer stack is laid The anti-reflective coating or reflective coating of each of the laser facets is embodied in the radiation coupling-out zone 27 and on the rear side region 28 opposite the radiation coupling-out zone 27. For example, the optical layer 7 laid on the radiation coupling-out region 27 can be embodied as an anti-reflection layer, while the optical layer 7 laid on the back side region 28 is embodied as a reflective layer. The optical layer 7 can be laid by a method commonly used for laying laser diode facets and fabricating a typical amorphous or partially crystalline layer.

In the exemplary embodiment illustrated, the crystal protective layer 6 is disposed between the optical layer 7 and the radiation coupling-out region 27 in this manner. In order to protect the radiation coupling-out region 27, it is sufficient if the crystal protective layer 6 has a thickness of several nanometers to several tens of nanometers, so that the crystal protective layer 6 does not affect the optical properties of the coating layer laid on the radiation coupling-out region 27 (subsequently It is determined by the optical layer 7). Alternatively, it is also possible to embody the crystal protective layer 6 as part of the optical layer 7 and have a suitably selected thickness.

FIG. 5B illustrates an exemplary embodiment in which a crystal protective layer 6 is disposed between the back side region 28 and the optical layer 7 in addition to the crystal protective layer 6 on the radiation coupling region 27 and the back side region 28. As a result, the backside region 28 can also be protected from harmful gases and solder that may migrate or diffuse to the backside region 28.

FIG. 5C illustrates another exemplary embodiment in which the optical layer 7 on the radiation coupling-out region 27 is formed by the crystal protective layer 6. For this purpose, the crystal protective layer 6 has a layer having desired anti-reflective or reflective properties, and a plurality of layers composed of different materials are preferred.

FIG. 5D illustrates another exemplary embodiment in which the optical layer 7 on the back side region 28 is also formed by the crystal protective layer 6. In this situation Next, the crystal protective layer 6 also has a layer which causes an anti-reflection or reflection property, and a plurality of crystal layers composed of different materials are preferable.

Figure 5E illustrates another exemplary embodiment in which a crystal protective layer 6 is laid over the optical layer 7 as compared to the exemplary embodiment of Figure 5A, whereby the optical layer 7 is disposed on the crystal protective layer 6, radiation The coupling out regions 27 are and thus covered by the crystal protective layer 6. As a result, first, the optical layer 7 can be protected by the crystal protective layer 6 in addition to the radiation coupling-out region 27. Furthermore, as an alternative to the dielectric material, it is also possible for the crystal protective layer 6 to also use a semiconductor material or a conductive material, such as one of the dielectric materials mentioned above in the general part.

In the exemplary embodiment of Figure 5F, a crystal protective layer 6 is also applied over the optical layer 7 on the back side region 28, which protects the optical layer 7 on the back side region 28 and the back side region 28.

FIG. 5G illustrates another exemplary embodiment illustrating a top view of the laser diode wafer 2, and wherein, in addition to the crystal protective layer 6 on the radiation coupling region 27 and the back side region 28, the crystal protection is laid. The layer 6 is on the side region 29 which interconnects the rear side region 28 with the radiation coupling region 27. As a result, for the interface between the laser diode 2, in particular the semiconductor layer and the semiconductor layer, all side protection can be achieved because the crystal protective layer 6 covers all side regions of the laser diode wafer 2. . In this case, as shown in Fig. 16, the crystal protective layer 6 covering the optical layer 7 can be laid. Alternatively, it is also possible to lay the crystal protective layer 6 directly on the radiation coupling-out zone and/or the backside zone 28.

The following figures illustrate other demonstrations of a laser diode assembly Specific embodiments are modifications and variations of the exemplary embodiments of FIGS. 2A, 2B, 3, 5A-5G. Therefore, the following description is to be construed as being limited to the details of the foregoing exemplary embodiments. In particular, the laser diode assembly described below may have a crystal protective layer and a housing cover at least on the radiation coupling region, even though the drawings are not explicitly illustrated.

Figure 6 illustrates an exemplary embodiment of a laser diode assembly 101 in which the housing portion 10 and the mounting portion 11 are compared to the laser diode assembly 100 of Figures 2A and 2B. A cover layer 12 composed of steel. As a result, in the case of a standard TO case, it is possible to realize the mounting area 13 composed of steel while improving the thermal conductivity with copper.

7A through 7C are schematic cross-sectional views (FIG. 7A) of a laser diode assembly 102, a plan view opposite the extending direction 110 (FIG. 7B) and a mounting area 13 according to another exemplary embodiment. Floor plan (Fig. 7C). In contrast to the exemplary embodiment described above, in the case of a laser diode assembly 102, a thermally conductive element 4 is disposed between the laser diode wafer 2, the mounting portion 11 of the housing 1. In particular, the heat-conducting element is embodied as a so-called heat sink and for enlarging the heat flow between the laser diode wafer 2 and the mounting portion 11 of the housing 1 in order to achieve the maximum possible entry into the housing 1 during heat transfer. Transition area.

In this case, as described above, the first solder layer 3 (the heat conducting member 4 is mounted on the mounting portion 11 of the casing 1) may be embodied to have a thickness greater than or equal to 2 μm, and a thickness greater than or equal to 3 μm. Preferably, a thickness greater than or equal to 5 microns is particularly preferred. In addition, the second solder layer 5 is disposed between the heat conductive element 4 and the laser diode wafer 2, and the laser 2 The polar body wafer 2 is mounted on the thermally conductive element 4 with the second solder layer. The second solder layer 5 also has a thickness greater than or equal to 2 microns, a thickness greater than or equal to 3 microns is preferred, and a thickness greater than or equal to 5 microns is particularly preferred. 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.

The mounting portion 11 may be formed of copper, as shown in the exemplary embodiment illustrated, or may have a steel cover layer 12, as illustrated in the description of Figure 6 and as shown by the dashed line in Figure 7A.

The laser diode 2 and the casing 1 have different coefficients of thermal expansion due to materials. Nitride-based semiconductor materials often have a coefficient of thermal expansion of about 5.6 x 10 ^-6 l/K and a thermal conductivity of about 100 W/mK, while copper has a coefficient of thermal expansion of about 16 to 18 x 10 ^-6 l/K and about 300 W. /mK thermal conductivity. The plurality of materials located therebetween (and thus, for example, the steel cover 12 of the mounting portion 11, the solder layers 3, 5 and the thermally conductive element 4) also have different coefficients of thermal expansion. The steel has a coefficient of thermal expansion of about 6 to 12 x 10 ^-6 l/K and a thermal conductivity of about 30 to 70 W/mK. For example, the thermally conductive element 4 may comprise or consist of aluminum nitride having a coefficient of thermal expansion of from about 4.5 to 5.7 x 10 ^-6 l/K and a thermal conductivity of from about 80 to 200 W/mK. Therefore, the thermal expansion coefficient of the aluminum nitride heat conductive element 4 is relatively well matched with the thermal expansion coefficient of the laser diode wafer 2. However, there is a significant difference in thermal expansion coefficient at the transition boundary between the aluminum nitride thermally conductive element 4 and the casing 1 (i.e., copper or copper coated copper).

Therefore, it is possible to use tantalum carbide, particularly 6H-SiC, as the material of the heat conductive member 4, particularly preferred, not aluminum nitride, although it has a thermal expansion coefficient of about 4.4 × 10 ^-6 l / K, it still has about Higher thermal conductivity from 200 to 500 W/mK. Alternatively, since the thermally conductive element 4 is also likely to use one of the following materials: a copper-tungsten alloy having a coefficient of thermal expansion of about 6 to 8 x 10 ^-6 l/K and a thermal conductivity of about 200 to 250 W/mK, the coefficient of thermal expansion is about 2.5 to 4×10 ^-6 l/K and boron nitride having a thermal conductivity of about 600 W/mK, a diamond having a thermal conductivity of about 1000 W/mK and a thermal expansion coefficient of 2.3×10 ^-6 l/K ( For example, diamonds produced by CVD). Although such materials have a relatively unfavorable thermal strain for the thermally conductive element 4, the laser diode assemblies described herein may be preferred because the greater thermal strain produced by these materials can be described herein. The solder layers 3, 5 are compensated. The solder layers 3, 5 may comprise indium based soft solder, for example, in order to provide the best possible compensation for thermally induced strain.

Features that are described and illustrated in the drawings and exemplary embodiments may be combined with each other according to other exemplary embodiments, even if such combinations are not explicitly illustrated in the drawings. In particular, the different housing forms, the application of the thermally conductive element 4 and the configuration of the one or more protective layers 6 on the laser diode wafer 2 can be combined with one another. Furthermore, the exemplary embodiments illustrated in the drawings may have alternative or additional features in accordance with the specific embodiments in the general.

With respect to the laser diode assembly described herein, the use of a copper-based housing 1 may result in thermally induced strain due to the different thermal expansion coefficients of the individual components of the laser diode assembly, such as in the housing 1 Between the elements 4, between the thermally conductive element 4, the laser diode wafer 2, or in the absence of the thermally conductive element 4, directly between the laser diode wafer 2 and the housing 1. In addition, during the process of manufacturing the housing portion, an uneven surface may occur due to different material compositions, in particular, at the mounting portion 11 In the case of a steel covering. Under other measures not described herein for the laser diode assembly, the advantages of the copper-based housing 1 may therefore be lost again because of the laser diode 2 and the housing 1 (or, if any, the thermally conductive element 4) The heat removal between the housing 1) is reduced. Stable coupling of the laser diode wafer 2 or the thermally conductive element 4 to the housing 1 can be achieved with the first solder layer 2 having a thickness greater than 2 microns (more preferably greater than 3 microns). In order to cope with the increased risk of increasing the solder supply: the solder particles may migrate through the surface of the laser diode wafer 2 (in particular, the laser facets 27, 28) and diffuse through the facet coating, which may result in a laser passing through The leakage current of the facets 27, 28, the laser diode 2 preferably has a crystal protective layer 6. With the crystal protective layer 6, it is again possible to achieve a substantial increase in the strength of the collapse field. As a result, it is possible to achieve protection against electrical collapse caused, for example, by solder layer upflow or p-type metallization over the facet.

As for the laser diode assembly described herein in accordance with the exemplary embodiments illustrated, the high thermal conductivity of the housing 1, the laser diode wafer 2 (if any, the thermally conductive element 4) and the housing 1 are excellent. The thermal connection, the radiation coupling out zone 27 is protected from environmental influences and the protection of the solder particles, and the high collapse strength of the coating of the radiation coupling out zone 27 is combined with each other, as a result, compared to conventional laser diode parts. It is possible to increase the light output power.

The present invention is not limited to the exemplary embodiments described above based on the description of the exemplary embodiments. Instead, the present invention encompasses any novel features and any combination of features, and in particular, any combination of features in the scope of the claims, even if such a feature or combination is not specifically described in the claims or exemplary embodiments.

2‧‧‧Laser Diode Wafer

6‧‧‧ crystal protective layer

7‧‧‧Optical layer

27‧‧‧radiation coupling area

28‧‧‧ Back side area

29‧‧‧ Side area

Claims (15)

A laser diode assembly includes a housing portion (10) and a mounting portion having a housing portion (10) coupled thereto and extending away from the housing portion (10) along an extending direction (110) ( a casing (1) of 11), and a laser diode chip (2) on the mounting portion (11), the laser diode chip having a semiconductor layer (21, 22, on the substrate (20) 23, 24) and an active layer (23) for illuminating, wherein the housing portion (10) and the mounting portion (11) have a body made of copper and at least the housing portion (10) is covered with steel. a first solder layer (3) having a thickness greater than or equal to 2 microns is disposed between the laser diode wafer (2) and the mounting portion (11), and the laser diode wafer (2) is laid The radiation protection layer (6) on which the crystal protective layer (6) is attached. The laser diode assembly of claim 1, wherein the crystal protective layer (6) is formed of a dielectric material. The laser diode assembly of claim 1 or 2, wherein the crystal protective layer (6) is formed of an oxide. The laser diode assembly according to any one of the preceding claims, wherein the crystal protective layer (6) has a plurality of crystal layers. The laser diode assembly according to any one of the preceding claims, wherein the optical layer (7) is laid in the radiation coupling region. (27) Upper. The laser diode assembly of claim 5, wherein the optical layer (7) is disposed between the radiation coupling region (27) and the crystal protective layer (6) and by the crystal The protective layer (6) is covered. The laser diode assembly of claim 5, wherein the crystal protective layer (6) is disposed between the radiation coupling region (27) and the optical layer (7). The laser diode assembly of claim 5, wherein the optical layer (7) is formed by the crystal protective layer (6). The laser diode assembly according to any one of the preceding claims, wherein the crystal protective layer (6) is laid on the rear side region of the laser diode chip (2). (28) The rear side region is located opposite the radiation coupling-out region (27). The laser diode assembly according to any one of the preceding claims, wherein the crystal protective layer (6) is placed in the laser diode (2) and connected thereto. The side region (28) is on the side region (29) of the radiation coupling-out region (27). The laser diode assembly according to any one of the preceding claims, wherein the first solder layer (3) has a thickness greater than or equal to 3 micrometers. The laser diode assembly according to any one of the preceding claims, wherein the heat-conducting element (4) is disposed on the laser diode chip (2) and the mounting portion ( 11) Between. a laser diode assembly as described in claim 12, The heat conducting element (4) is fixed to the mounting portion (11) with the first solder layer (3), and the laser diode chip (2) is second with a thickness greater than or equal to 2 microns. A solder layer (5) is attached to the thermally conductive element (4). The laser diode assembly of claim 12, wherein the thermally conductive element (4) comprises aluminum nitride, tantalum carbide, boron nitride, copper tungsten alloy or diamond. A laser diode assembly according to any one of the preceding claims, wherein the housing cover (14) is laid on the housing portion (10) and welded to the housing The portion (10) and the mounting portion (11) protrude from the housing portion (10) into the housing cover (14) along the extending direction (110).