DE102011123129B4 - Laser light source with mode filter structure - Google Patents

Abstract

Laser light source with a ridge waveguide structure, comprising
a semiconductor layer sequence (10) with a plurality of functional layers (4) and an active region (45) which is suitable for generating laser light during operation,
wherein at least one of the functional layers (4) is formed as a ridge (11) of the ridge waveguide structure and
wherein the semiconductor layer sequence (10) has a mode filter structure (6) which is formed perpendicular to a main extension plane of the functional layers (4) below the web (11),
wherein the main extension plane is perpendicular to an arrangement direction of the semiconductor layer sequence (10),
wherein the semiconductor layer sequence (10) has at least one functional layer as a mode filter structure (6) which has a damaged structure (66) which is produced by evaporating a material of the semiconductor layer sequence (10) with a laser,
wherein the laser light source has a further mode filter structure (6), and the further mode filter structure (6) has different ridge heights (110, 110') on two opposite ridge side surfaces (111, 112), so that an asymmetric waveguide is produced, and
wherein the mode filter structures (6) attenuate higher modes that occur in addition to a fundamental mode in the laser light source.

Description

For projection applications, laser sources operating in fundamental mode or monomode with ever-increasing power are required to achieve sufficient brightness while still maintaining very high efficiency for increasing screen sizes. In addition, a low aspect ratio of the laser beam is often desirable to simplify complex and lossy lens systems.

In typical index-guided laser structures, such as laser diodes with ridge waveguide structures, monomode operation is achieved by having an extremely narrow laser ridge width. However, this poses a significant disadvantage in the high technological requirements, as conventional exposure and etching technologies reach their limits. Another major disadvantage of such narrow ridge widths is the increased operating voltages required to operate such laser diodes.

Another way to improve the monomode performance of a laser diode with a ridge waveguide structure is to use a low ridge height. The resulting weak optical guidance allows only the fundamental mode to oscillate. However, this also leads to increased threshold currents, since weak waveguide or a low ridge height is usually associated with current spreading.

It is also known to apply absorber layers to a thin passivation layer adjacent to the laser ridge. However, since this configuration requires very thin passivation layers, electrical problems can arise, such as dielectric strength or leakage currents. Another disadvantage is that it is generally impossible to prevent the fundamental mode from being attenuated by the absorber, which results in losses in the laser parameters, particularly reduced efficiency.

The printed matter JP 2005 - 183 821 A is directed to a light-emitting semiconductor device.

The printed matter DE 10 2006 046 297 A1 relates to a semiconductor laser.

The printed matter JP 2004-179 350 A discloses a nitride semiconductor laser and a method for manufacturing the same.

The printed matter DE 199 63 807 A1 relates to a stripe laser diode element.

The printed matter CN 101 710 670 A is directed at a semiconductor laser with an emission wavelength of 808 nm.

The printed matter US 2008 / 0 273 564 A1 discloses a semiconductor laser element array.

The printed matter US 2007 / 0 258 495 A1 relates to a semiconductor laser diode, a semiconductor optical amplifier and an optical communication device.

The printed matter US 2003 / 0 219 053 A1 concerns an index-guided laser structure.

The printed matter US 2006 / 0 193 353 A1 discloses a high-power single-mode semiconductor laser and a method for manufacturing the same.

The printed matter US 2006 / 0 011 946 A1 addresses a nitride semiconductor laser element.

The printed matter DE 10 2008 012 859 A1 describes a laser light source and a method for producing a laser light source.

The printed matter US 5 070 510 A discloses a semiconductor laser device.

An object of at least one embodiment is to provide a laser light source with a semiconductor layer sequence.

This object is achieved by a subject matter having the features of the independent patent claim. Advantageous embodiments and further developments of the subject matter and the method are characterized in the dependent claims and will become apparent from the following description and the drawings.

The laser light source with a ridge waveguide structure has a semiconductor layer sequence with a plurality of functional layers and an active region which is suitable for generating laser light during operation, wherein at least one of the functional layers is designed as a ridge of the ridge waveguide structure and wherein the semiconductor layer sequence has a mode filter structure which is designed perpendicular to a main extension plane of the functional layers below the ridge, wherein the main extension plane is perpendicular to an arrangement direction of the semiconductor layer sequence, wherein the semiconductor layer sequence has at least one functional layer as a mode filter structure which has a damaged structure which is formed by evaporating a material of the semiconductor layer sequence with generated by a laser,
wherein the laser light source has a further mode filter structure, and the further mode filter structure has different ridge heights on two opposite ridge side surfaces, so that an asymmetric waveguide is produced, and
where the mode filter structures attenuate higher modes that occur in addition to a fundamental mode in the laser light source.

According to at least one embodiment, a laser light source comprises a semiconductor layer sequence comprising a plurality of functional layers. In particular, the semiconductor layer sequence comprises an active layer with an active region that can generate laser light during operation of the laser light source. The functional layers each have a main plane of extension that is perpendicular to the arrangement direction of the superimposed functional layers.

According to a further embodiment, the laser light source is designed as an edge-emitting laser diode. For this purpose, the semiconductor layer sequence has a side surface that is at least inclined with respect to the main extension plane of the functional layers and, for example, perpendicular or substantially perpendicular thereto, and which is designed as a radiation outcoupling surface, such that the laser light can be emitted via the radiation outcoupling surface during operation. The semiconductor layer sequence can preferably have a first and a second waveguide layer, between which the active region is arranged. In particular, the semiconductor layer sequence can have an optical resonator for the laser light. This can in particular comprise a first at least partially reflective layer, for example a mirror layer, on the radiation outcoupling surface and/or a second at least partially reflective layer, for example a mirror layer, on a side surface of the semiconductor layer sequence opposite the radiation outcoupling surface, between which the active region is arranged.

The semiconductor layer sequence can be embodied as an epitaxial layer sequence or as a radiation-emitting semiconductor chip with an epitaxial layer sequence, i.e. as an epitaxially grown semiconductor layer sequence. The semiconductor layer sequence can be embodied, for example, on the basis of InGaAlN. InGaAlN-based semiconductor chips and semiconductor layer sequences include, in particular, those in which the epitaxially produced semiconductor layer sequence generally has a layer sequence of different individual layers, which contains at least one individual layer comprising a material from the III-V compound semiconductor material system In _x Al _y Ga _1-xy N with 0 ≤ x ≤ 1, 0 ≤ y ≤ 1 and x + y ≤ 1. Semiconductor layer sequences that have at least one active layer based on InGaAlN can, for example, preferably emit electromagnetic radiation in an ultraviolet to green wavelength range.

Alternatively or additionally, the semiconductor layer sequence or the semiconductor chip can also be based on InGaAlP, i.e. the semiconductor layer sequence can have different individual layers, of which at least one individual layer has a material from the III-V compound semiconductor material system In _x Al _y Ga _1-xy P with 0 ≤ x ≤ 1, 0 ≤ y ≤ 1 and x + y ≤ 1. Semiconductor layer sequences or semiconductor chips which have at least one active layer based on InGaAlP can, for example, preferably emit electromagnetic radiation with one or more spectral components in a green to red wavelength range.

Alternatively or additionally, the semiconductor layer sequence or the semiconductor chip may also comprise other III-V compound semiconductor material systems, for example, an AlGaAs-based material, or II-VI compound semiconductor material systems. In particular, an active layer comprising an AlGaAs-based material may be suitable for emitting electromagnetic radiation with one or more spectral components in a red to infrared wavelength range.

The semiconductor layer sequence may further comprise a substrate on which the above-mentioned III-V or II-VI compound semiconductor material system is deposited. The functional layers may be grown on the substrate, which is then formed as a growth substrate. Alternatively, the functional layers may be transferred to the substrate after growth, which is then formed as a carrier substrate. The substrate may comprise a semiconductor material, for example, an above-mentioned compound semiconductor material system. In particular, the substrate may comprise GaP, GaN, SiC, Si, Ge, and/or sapphire, or be made of such a material.

The semiconductor layer sequence can have, for example, a conventional pn junction, a double heterostructure, a single quantum well structure (SQW structures) or a multiple quantum well structure (MQW structures) as active regions in the active layer. In addition to the active layer with the active region, the semiconductor layer sequence can comprise further functional layers and functional regions, such as p- or n-doped charge carrier transport layers, p- or n-doped confinement, cladding or waveguide layers, barrier layers, planarization layers, buffer layers, protective layers and/or Electrodes and combinations thereof. The electrodes can each have one or more metal layers containing Ag, Au, Sn, Ti, Pt, Pd, Rh, and/or Ni. Such structures relating to the active layer or the other functional layers and regions are known to the person skilled in the art, particularly with regard to design, function, and structure, and are therefore not explained in detail here.

In addition, additional layers, such as buffer layers, barrier layers and/or protective layers, can also be arranged perpendicular to the growth direction of the semiconductor layer sequence, for example around the semiconductor layer sequence, for example on the side surfaces of the semiconductor layer sequence.

According to a further embodiment, the laser light source has a ridge waveguide structure. For this purpose, at least one or more functional layers of the semiconductor layer sequence are structured such that the at least one or more layers form a ridge that extends in one direction, the ridge extension direction, parallel to the main extension plane of the functional layers. In particular, such a configuration of the semiconductor layer sequence, which can also be referred to as a "ridge structure," can be suitable, depending on its width and height and due to the so-called index guidance due to the ridge-shaped structure and an associated refractive index jump, to enable the formation of a transverse fundamental mode in the active region. The ridge can extend, in particular, from the radiation output surface to the side surface of the semiconductor layer sequence opposite the radiation output surface.

To produce the ridge waveguide structure, for example, the semiconductor layer sequence with the aforementioned functional layers and the active region can be provided. The ridge can be created through a mask using an ablation process, such as etching, on a main surface of the semiconductor layer sequence, which is arranged parallel to the main extension plane of the functional layers. The width of the ridge can be adjustable using a photolithographically produced mask.

According to a further embodiment, the semiconductor layer sequence has a mode filter structure. The mode filter structure can be particularly suitable for attenuating higher modes that may occur in the laser light source alongside a fundamental mode.

According to a further embodiment, the mode filter structure is embodied as part of the web and/or formed along a main extension plane of the functional layers adjacent to the web and/or formed perpendicular to a main extension plane of the functional layers below the web. The mode filter structure may comprise one or more of the elements, features, and/or embodiments described below.

According to a further embodiment, the web has a horizontal web width perpendicular to the web extension direction and parallel to the main extension plane of the functional layers. Perpendicular to the main extension plane of the functional layers and perpendicular to the web extension direction, the web can have a vertical web width. In other words, the horizontal web width can be the width of the web that the web has in a plan view of the top side of the laser light source with the web. The vertical web width can be the width of the web that the web has in a section perpendicular to the main extension planes of the functional layers and perpendicular to the web extension direction. In particular, as a mode filter structure, the web can have a varying horizontal web width and/or a varying vertical web width.

According to a further embodiment, the horizontal web width has at least one thickening and/or a constriction. This can mean, in particular, that the horizontal web width increases along the web extension direction and then decreases again to form a thickening, and/or decreases and then increases again to form a constriction. The at least one thickening and/or constriction can be designed as a kink or step in the horizontal web width or as a continuously changing web width.

By widening the ridge in the form of one or more thickenings of the horizontal ridge width, the contact area of the ridge on the functional layer or sub-layer on which the ridge is directly arranged and to which the ridge directly adjoins, and/or the contact area of an electrode layer on the ridge to the ridge or to the functional layers can be increased at one or more locations, thereby reducing the operating voltage of the laser light source and thus improving efficiency. In particular, by continuously changing the varying horizontal ridge width, losses in the laser light source that can occur with abrupt changes in the ridge width can be reduced or completely avoided. Smooth transitions, such as those achieved, for example, by variations of exponential functions, can be particularly preferred. Sine, cosine, tangent and/or Gaussian curves and combinations thereof can be achieved.

berechnet werden, wobei d die horizontale Stegbreite an der genannten Stelle ist, n₂ der effektive Brechungsindex unter dem Steg in der Halbleiterschichtenfolge und n₁ der effektive Brechungsindex neben dem Steg.According to a further embodiment, the web has a varying horizontal web width with at least one thickening and/or a constriction, wherein the horizontal web width is narrower at at least one location than the so-called cut-off width to achieve single-mode operation. This can be determined using the known relationship $$\text{d}=\mathrm{\lambda }/2\left[{\left({\text{<figure-callout id="2" label="n" filenames="DE102011123129B4\_0002.png" state="{{state}}">n</figure-callout>}}_2^2-{\text{<figure-callout id="1" label="n" filenames="DE102011123129B4\_0002.png" state="{{state}}">n</figure-callout>}}_1^2\right)}^{1/2}\right]$$

where d is the horizontal ridge width at the specified location, n ₂ is the effective refractive index below the ridge in the semiconductor layer sequence and n ₁ is the effective refractive index next to the ridge.

According to a further embodiment, the web has a web width which is in the range from 0.3 µm to 200 µm inclusive, preferably in the range from 0.5 µm to 10 µm inclusive, and particularly preferably in the range from 0.8 µm to 3 µm inclusive.

According to a further embodiment, the ridge has a thickening with respect to its horizontal ridge width near or at the radiation outcoupling surface and/or the side surface of the semiconductor layer sequence opposite the radiation outcoupling surface. This makes it possible to reduce the power density directly at the radiation outcoupling surface, whereby higher output powers can be achieved without destroying the radiation outcoupling surface of the laser light source (COMD: "catastrophic optical mirror damage"). Alternatively, the ridge can have a thickening of the horizontal ridge width between the radiation outcoupling surface and the side surface of the semiconductor layer sequence opposite the radiation outcoupling surface, while the horizontal ridge width has a constriction or taper at the radiation outcoupling surface or the side surface opposite the radiation outcoupling surface. This makes it possible to generate a wider lateral far field.

By means of a web with a varying web width, which has at least one thickening and/or a constriction, a combination of the advantages of a narrow web and a wide web can be achieved, wherein a narrow web or the narrow web regions can achieve a low aspect ratio of the emitted laser beam and a pronounced monomode guidance, while a wide web or the wide web regions can improve the electrical contact, whereby the operating voltage can be reduced.

According to a further embodiment, the vertical ridge width has a constriction. The constriction can, for example, comprise the active region or at least a functional layer above the active region. This can mean that the constriction of the vertical ridge width is arranged in the region of the active layer with the active region or above it. Because the constriction makes an upper part of the ridge wider than the lower part, which is more relevant for waveguiding, a larger contact area can be created between the semiconductor layer sequence and an electrode layer applied thereon. This can, in particular, achieve a reduction in the voltage for operating the laser light source, thereby increasing efficiency. This can be particularly advantageous for a laser light source with a semiconductor layer sequence based on a nitride compound semiconductor material, since with this material, in particular, the contact resistances with p-doped semiconductor layers are high compared to other material systems.

According to a further embodiment, the ridge as a mode filter structure has a varying ridge height perpendicular to a main extension plane of the functional layers. In particular, this can mean that the ridge height varies along the ridge extension direction. Regions in which the ridge has a high ridge height, i.e. in which the part of the semiconductor layer sequence adjacent to the ridge has a depression, can bring about a reduction in current spreading and better overlap of the optical mode with the electrically pumped region, whereby a lower laser threshold and thus good efficiency can be achieved. Regions with a lower ridge height, i.e. regions of the semiconductor layer sequence or the part of the semiconductor layer sequence adjacent to the ridge that have a raised area compared to other parts, can ensure weaker waveguiding, so that higher modes experience greater losses and can thus be attenuated or, more preferably, can no longer be guided at all. The transitions between regions with a high ridge height and regions with a low ridge height can be abrupt, i.e., in particular, stepped or in the form of kinks, in the height profile of the part of the semiconductor layer sequence adjacent to the ridge. Alternatively, the ridge height can also vary continuously along the ridge extension direction.

According to a further embodiment, the web has web side surfaces that delimit the web in a direction perpendicular to the web extension direction and that run along the web extension direction. The web can have different web heights for the two side surfaces, at least partially or along the entire web, as a mode filter structure. Such an asymmetric design of the web heights on the web side surfaces can create asymmetric waveguiding that can particularly preferably only guide one mode. The higher web height on one side of the web can reduce the current spreading on this side, which can lead to an increase in efficiency while simultaneously maintaining single-mode operation. In addition, the web height on one or both web side surfaces can vary along the web extension direction.

According to a further embodiment, a passivation layer is arranged next to the ridge as a mode filter structure, which passivation layer varies along the ridge extension direction, for example, with regard to its composition and/or material. By varying the passivation along the ridge, a variation of the refractive index along the ridge can be achieved, whereby a region with a lower refractive index can have the same effect as an increase in the ridge height. In particular, the passivation layer can vary continuously with regard to its composition and/or material and in particular with regard to its refractive index. This can be achieved, for example, by two passivation layers, of which one passivation layer becomes thinner along the ridge extension direction and a second passivation layer applied thereon becomes thicker. In particular, the passivation layer can be directly adjacent to the ridge on at least one ridge side surface. Particularly preferably, a passivation layer is arranged adjacent to both ridge side surfaces.

According to a further embodiment, the laser light source, as a mode filter structure, has different passivations on the two ridge side surfaces adjacent to the ridge, which, for example, have different refractive indices. This allows a similar effect to that described above for different ridge heights to be achieved on the ridge side surfaces.

According to a further embodiment, the ridge as a mode filter structure has a curved ridge extension direction. A curved ridge extension direction can be recognizable in a plan view of the ridge by a curved profile of the ridge. This can mean, in particular, that the ridge is not exclusively mirror-symmetrical to the optical axis of the laser light source. The optical axis can be defined, in particular, by the direction in the semiconductor layer sequence, in particular in the active region, along which the laser radiation is generated. The emission direction in which the laser light is emitted by the laser light source from the radiation output surface can be an extension of the optical axis.

According to a further embodiment, the web side surfaces of a web with a curved web extension direction are parallel or at least approximately parallel. This can simplify processability and/or increase reproducibility from laser light source to laser light source.

According to a further embodiment, the bridge has a curved bridge extension direction, which is formed by at least one bend in the bridge and/or at least one continuous change in direction of the bridge relative to the optical axis. The at least one bend or the at least one continuous change in direction can be defined by a defined angle.

By using a curved ridge extension direction, it may be possible to attenuate higher modes in the active region more strongly, whereby a single-mode behavior can be achieved even with a ridge width that is larger than the cut-off ridge width described above.

According to a further embodiment, a mode filter structure can be combined with a curved ridge extension direction and a varying passivation along the ridge extension direction and/or on the two ridge side surfaces. Depending on the curvature, a curved ridge can have an asymmetric far field. To compensate for this, in the case of a curved ridge extension direction, in particular in the case of a curved, curved ridge extension direction with one or more curves, a passivation can be arranged on one or more inner curves that has a higher absorption than a passivation on the corresponding outer curve. This can influence the phase of the optical mode such that a symmetrical radiation profile or far field is generated.

According to a further embodiment, the web is delimited by two web side surfaces running along the web extension direction, wherein, as a mode filter structure, at least a partial region of a web side surface exhibits oxidation. This can mean, in particular, that at least a partial region of a web side surface, preferably one web side surface and particularly preferably both web side surfaces, are oxidized at least in partial regions. For this purpose, the web can have at least one aluminum-containing layer whose side surfaces, which form a partial region of the web side surfaces, are oxidized.

According to a further embodiment, the ridge borders a functional layer of the semiconductor layer sequence, which comprises a conductivity-changing and/or light-absorbing material as a mode filter structure. Such a material, which may be, for example, a dopant such as silicon, an electrically insulating substance such as hydrogen, or a light-absorbing substance such as germanium, can be introduced by implantation and/or diffusion into at least partial regions of the functional layer adjacent to the ridge. Such regions can serve as current and/or mode apertures, through which higher modes can be attenuated by lateral current limitation and/or appropriate waveguiding.

According to a further embodiment, the semiconductor layer sequence has at least one functional layer as a mode filter structure, which at least partially has a damaged structure next to the ridge and/or below the ridge. A damaged structure can be created, for example, after the semiconductor layer sequence has grown and the ridge has been formed, by at least partially evaporating semiconductor material of the semiconductor layer sequence in at least one functional layer. Evaporation can be achieved, for example, by irradiating the semiconductor layer sequence with laser radiation, in particular short-pulse laser radiation, which, with appropriate focusing, can damage the semiconductor material in targeted areas. In particular, the laser radiation can be selected such that a component, for example, the group V material in the case of a group III-V compound semiconductor material, is at least partially evaporated. The damaged area can be formed in a functional layer directly adjacent to the ridge. Additionally or alternatively, the semiconductor layer sequence may have a damaged region below and/or laterally offset next to the ridge and below the ridge, for example, on a side of the active region facing away from the ridge. A current and/or mode gate can also be achieved through such a damaged region.

According to a further embodiment, the laser light source, as a mode filter structure, has at least two of the aforementioned mode filter structure features and/or embodiments. This can mean, in particular, that the laser light source, as a mode filter structure, has a varying ridge width and/or a varying ridge height and/or a varying passivation along the ridge extension direction. This can also mean that the ridge, as a mode filter structure, additionally or alternatively has a curved ridge extension direction and/or implanted or doped regions and/or damaged regions.

The embodiments of the mode filter structure mentioned here may make it possible to optimally adjust the mode profile of the laser light source to high efficiency, a desired far-field width and single-mode operation.

Further advantages and advantageous embodiments and developments of the invention will become apparent from the examples described below in conjunction with the figures.

• 1A bis 1C schematische Darstellungen von Laserlichtquellen mit einer Stegwellenleitstruktur,
• 2A bis 2N schematische Darstellungen von Laserlichtquellen mit einer variierenden horizontalen Stegbreite gemäß mehreren Beispielen,
• 3A bis 3M schematische Darstellungen von Laserlichtquellen mit gekrümmten Stegerstreckungsrichtungen gemäß weiteren Beispielen,
• 4A bis 6 schematische Darstellungen von Laserlichtquellen mit variierenden Steghöhen,
• 7 schematische Darstellung einer Laserlichtquellen mit einer variierenden Passivierung gemäß einem weiteren Beispiel,
• 8A bis 8B schematische Darstellungen von Laserlichtquellen mit variierenden Passivierungen gemäß weiteren Beispielen,
• 9A bis 10C schematische Darstellungen von Laserlichtquellen mit variierenden vertikalen Stegbreiten,
• 11A bis 11C schematische Darstellungen einer Laserlichtquelle mit einer Oxidierung von Stegseitenflächen gemäß weiteren Beispielen,
• 12A bis 12D schematische Darstellungen von Laserlichtquellen mit die Leitfähigkeit ändernden, den Brechungsindex ändernden und/oder Licht absorbierenden Materialien gemäß weiteren Beispielen,
• 13A bis 14B schematische Darstellungen von Laserlichtquellen mit Bereichen mit einer geschädigten Struktur gemäß weiteren Beispielen und
• 15A bis 15G schematische Darstellungen von Laserlichtquellen mit Streulichtfiltern gemäß weiteren Beispielen.

They show:

• 1A to 1C schematic representations of laser light sources with a ridge waveguide structure,
• 2A to 2N schematic representations of laser light sources with a varying horizontal web width according to several examples,
• 3A to 3M schematic representations of laser light sources with curved web extension directions according to further examples,
• 4A to 6 schematic representations of laser light sources with varying web heights,
• 7 schematic representation of a laser light source with a varying passivation according to another example,
• 8A to 8B schematic representations of laser light sources with varying passivations according to further examples,
• 9A to 10C schematic representations of laser light sources with varying vertical bar widths,
• 11A to 11C schematic representations of a laser light source with oxidation of web side surfaces according to further examples,
• 12A to 12D schematic representations of laser light sources with conductivity-changing, refractive index-changing and/or light-absorbing materials according to further examples,
• 13A to 14B schematic representations of laser light sources with areas with a damaged structure according to further examples and
• 15A to 15G schematic representations of laser light sources with stray light filters according to further examples.

In the examples and figures, identical or functionally identical components may be provided with the same reference numerals. The illustrated elements and their relative sizes are generally not to scale; rather, individual elements, such as layers, components, structural elements, and regions, may be exaggeratedly thick or oversized for clarity and/or clarity.

To describe the basic characteristics of a laser light source with a ridge waveguide structure, 1A A schematic spatial representation of a laser light source with a ridge waveguide structure, as known from the prior art, is shown. In particular, the known ridge waveguide structure is formed by a ridge 11 having a constant ridge height 110 and a constant ridge width 113 along the shown rectilinear ridge extension direction AA.

The laser light source comprises a semiconductor layer sequence 10 with a substrate 1, on which a plurality of functional, epitaxially grown layers 4 are applied. The functional layers 4 each have a main extension plane that is perpendicular to the arrangement direction of the functional layers. In the example shown, the semiconductor layer sequence 10 is based on an InGaAlN compound semiconductor material as described above in the general section. The functional layers 4 are formed as n- and p-doped cladding layers 41, 44 and waveguide layers 42, 43, as well as an active layer 40 with an active region 45. The active layer 40 can, for example, be formed as a multiple quantum well structure with 1 to 5 quantum films arranged between barrier layers. Furthermore, in addition to the functional layers shown, further functional layers, such as one or more contact layers and/or intermediate layers, can be present.

As an alternative to the nitride-based semiconductor material described here, the semiconductor layer sequence 10 can also comprise, for example, phosphide- and arsenide-based semiconductor materials.

The substrate 1 can be a growth substrate on which the functional layers 4 are grown epitaxially. Alternatively, the semiconductor layer sequence 10 can be produced using thin-film technology. This means that the functional layers 4 are grown on a growth substrate and subsequently transferred to a carrier substrate, which then forms the substrate 1 of the semiconductor layer sequence 10. Depending on the growth technique, the n-conducting layers or the p-conducting layers of the semiconductor layer sequence 10 can face the substrate 1.

In the example shown, the electrical contacting of the semiconductor layer sequence 10 is effected via an electrode 2 on the underside of the substrate 1 facing away from the functional layers 4 and via an electrode 3 on the upper side of the semiconductor layer sequence 10 opposite the substrate 1. The electrodes 2 and 3 can each have one or more metal layers, for example with Ag, Au, Sn, Ti, Pt, Pd, Rh and/or Ni.

As an alternative to electrical contacting through the substrate 1, the electrical contact 2 can also be arranged on the same side of the substrate 1 as the functional layers 4 and next to the active layer 40. This type of contacting is particularly suitable for electrically contacting the functional layers 4 on the substrate side when they are arranged on an electrically non-conductive substrate 1.

Furthermore, the semiconductor layer sequence 10 has a radiation output surface 12 and an opposite side surface 13 formed as a rear side, each of which has an at least partially reflective coating (not shown). As a result, the radiation output surface 12 and the rear side surface 13 form an optical resonator. The respective at least partially reflective coating can, for example, comprise or consist of a Bragg mirror layer sequence and/or reflective metal layers.

Passivation layers for protecting the semiconductor layer sequence can also be applied on or over surfaces of the semiconductor layer sequence 10 (not shown).

The cladding layer 44 arranged on the upper side of the active layer 40 applied to the substrate 1 is partially formed as a ridge 11 in the example shown and forms a so-called ridge waveguide structure or "ridge" structure as described in the general part. Alternatively, the ridge 11 can also be formed as part of further functional layers 4. The ridge 11 has ridge side surfaces 111, 112 which are arranged along the ridge The ridge waveguide structure with the ridge 11 is produced after the semiconductor layer sequence 10 has been produced by applying the functional layer 4 to the substrate 1 by etching. For this purpose, the semiconductor layer sequence 10 can, for example, also have a functional layer formed as an etch stop layer. The ridge height 110 thus corresponds to the etching depth during the formation of the ridge 11.

As an alternative to producing the web 11 by etching, it can also be grown by selective growth as part of the semiconductor layer sequence 10.

The ridge waveguide structure with ridge 11 enables the formation of laser light in the active layer 40, whereas unwanted additional laser modes can be suppressed to a certain extent compared to ridgeless laser light sources. In particular, the active layer 40 has the active region 45, which is predetermined, among other things, by the width of ridge 11 and is indicated in the example shown by the hatched area in the active layer 40. The active region 45 extends over the entire length of the active layer 40 in the resonator formed by the radiation output surface 12 and the rear side surface 13. In the active region 45, the semiconductor layer sequence 10 can generate laser light during operation by stimulated emission, which can be emitted via the radiation output surface 12.

In addition to the ridge extension direction AA, a vertical sectional plane BB through the semiconductor layer sequence 10 and a viewing direction CC as a top view of the semiconductor layer sequence 10 and in particular the ridge waveguide structure with the ridge 11 are also indicated for the description of the following examples.

In the 1B and 1C are schematic sectional views of laser light sources along the vertical section plane BB from 1A The semiconductor layer sequences 10 of the laser light sources of the 1B and 1C can be used, for example, as the semiconductor layer sequence according to example in 1A In addition, the laser light sources of the 1B and 1C a passivation 5, which is arranged next to the web 11. The passivation 5 can be provided, for example, for electrical insulation, for protecting the web and the semiconductor layer sequence 10, for facilitating the application of the electrode 3 and/or for adapting the refractive index jump at the web 11 or at the semiconductor layer sequence 10. While in 1B as well as in the 1A the web 11 is designed as a free-standing web, the laser light source of the 1C a so-called "tripod" structure, in which the semiconductor material of the semiconductor layer sequence 10 to the right and left of the ridge 11 is removed only in a narrow trench and not across the entire surface. This can result in better protection against scratches and/or mechanical stress on the ridge 11.

Furthermore, it is also possible to form the ridge 11 as a so-called buried heterostructure. After the ridge is formed, it is epitaxially overgrown with additional semiconductor layers.

The following examples describe variants according to the invention of the 1A to 1C shown known designs of laser light sources with ridge waveguide structures, which, compared to the known laser light sources of the 1A to 1C Mode filter structures 6. In addition to the design shown in the following examples, these can also be designed in a tripod structure or as a buried heterostructure.

In the 2A to 3M Below are shown top views of semiconductor layer sequences 10 of laser light sources according to several examples, wherein the top views are each in the viewing direction CC in 1A are equivalent to.

In the 2A to 2L Laser light sources are semiconductor layer sequences 10 with ridges 11 shown, which as a mode filter structure 6 parallel to the main extension plane of the functional layers and perpendicular to the ridge extension direction AA have a varying horizontal ridge width 113, 113', 113'', as in the 2A and 2D In particular, the horizontal web width in the plan view of the semiconductor layer sequence 10 shown in each case varies along the 2A and 2D indicated web extension direction AA.

In particular, the webs 11 of the laser light source of the examples according to the 2A to 2L Due to the varying horizontal ridge width, the mode filter structure 6 has 6 thickened portions 61 and/or 62 constrictions, which can achieve improved efficiency and/or better beam quality compared to known laser light sources with ridge waveguide structures with a constant ridge width. Thus, by widening the ridge width in the form of the thickened portions 61 at one or more locations, the contact area for supplying current to the active layer can be increased, thereby reducing the operating voltage and thus improving efficiency. The thickened portion 61 or the widened portion of the ridge width 113, 113' can be used, for example in 2A shown, abruptly, i.e. step-like. Preferably, the thickening 61 or the constriction 62 can be formed by a continuous or at least partially continuous transition of the web width, for example by a linear shape, as in 2B shown, or by circular and/or elliptical shapes, such as in 2C Furthermore, it can be particularly advantageous if the horizontal web width 113, 113', 113'' varies in the form of smooth transitions, as can be achieved, for example, by variations of exponential functions, sine, cosine, tangent and/or Gaussian curves and combinations thereof, as shown in the 2D to 2L Such a smooth transition can reduce or even completely avoid losses in the laser light source that could occur with too abrupt changes in the ridge width.

The mode filter structures 6 of the examples of 2A to 2L are designed to be axially symmetrical to the web extension direction AA, which also corresponds to the optical axis of the laser light sources.

In the 2M and 2N Two examples of mode filter structures 6 are shown, which have ridge width changes formed asymmetrically to the optical axis of the laser light source. Purely as an example, these are shown in the 2M and 2N in the form of the thickenings 61 of the horizontal ridge width. Due to the asymmetrical shape of the ridge, or rather, the shape that is not symmetrical to the optical axis, higher modes can be advantageously suppressed, since these are more strongly attenuated by the irregularities in the ridge width than the fundamental mode.

As an alternative to the number of thickenings 61 and/or constrictions 62 shown in the examples, more thickenings 61 and/or constrictions 62 may also be present. In particular, the shapes of the thickenings 61 and/or constrictions 62 shown in the various examples can also be combined with one another.

Particularly preferably, the horizontal ridge width 113 is preferably smaller at the narrowest point than the cut-off ridge width described in the general section to fulfill the single-mode condition. At other points, the ridge 11 can also be wider than the cut-off ridge width.

Depending on the desired radiation angle, the at least one thickening 61 and/or the at least one constriction 62 can be arranged near the facets, i.e. near the radiation output surface 12 and/or the rear side surface 13 opposite the radiation output surface and/or rather in the interior of the web 11 along the web extension direction AA. A widening 61 of the web 11 towards the facets, as for example in the 2F , 2K and 2L shown, has the additional advantage that the power density is reduced directly at the facet. This allows higher output powers to be achieved without damaging the facets, in particular the radiation output surface 12 of the laser light source. If a wider lateral far field is desired, it can be advantageous if the horizontal ridge width in the facet area is rather narrow, as for example in the 2A to 2E and 2G to 2J is shown.

In order to simplify the processability and to increase the reproducibility of different similarly designed laser light sources, it is advantageous if the edges and thus the side surfaces of the web 11 in the facet area preferably run at least approximately parallel, as in the 2A to 2E, 2H, 2I and 2J is shown.

In the 3A to 3H Laser light sources are shown, each having a ridge 11, which as a mode filter structure 6 has a curved ridge extension direction A, AA', AA'', as shown by way of example in 3A As a result, the bridge is in the position shown in the 3A to 3I shown examples are not mirror-symmetrical to the optical axis, which despite the varying direction of the web extension in the examples of 3A to 3I is formed in a straight line between the radiation output surface 12 and the rear side surface 13. Such curved ridge shapes allow higher modes to be attenuated more effectively than the fundamental mode, whereby the minimum ridge width can also be wider than the above-mentioned cut-off ridge width in order to still achieve single-mode behavior.

As in 3A As shown, the web 11 can have kinks with defined angles, so that the web extension direction A, AA', AA'' can change abruptly. As in the examples of 3B to 3I As shown, the web extension direction can also vary continuously, which can avoid losses compared to an overly abrupt change in the web extension direction.

Particularly preferably, the web side surfaces in the region of the facets 12, 13 are formed perpendicular or at least approximately perpendicular to these. 3A and 3B As shown, the positions of the web 11 on the facets 12, 13 may be offset from each other. the 3C to 3H As shown, the positions of the ridge 11 at the facets 12, 13 can overlap each other in a projection along the optical axis, as is the case with a straight ridge, while the ridge 11 between the facets 12, 13 varies relative to the ridge ends at the facets 12, 13. The ridge extension direction can, as in 3I shown, have a change in direction or, as in the 3A and 3B shown, two changes of direction, which according to 3A follow each other abruptly and according to the 3B and 3I continuously and gradually merge into one another. In the 3C to 3H , ridges with mode filter structures 6 are shown, which are formed by a plurality of changes in the direction of the ridge extension. This allows increased attenuation of higher modes to be achieved. As shown in the 3F to 3I As shown, the varying web extension directions can additionally be combined with thickenings 61 or constrictions 62 of the horizontal web width.

In the 3 years and 3K further examples of mode filter structures 6 with a curved ridge extension direction are shown, which are purely exemplary curved like the ridges 11 of the examples of 3B and 3C Due to the ridge curvature, the laser light sources of the examples shown can have an asymmetric far field. This can be compensated for by arranging a passivation 63 on the inner curves of the curved ridges 11 as a further part of the mode filter structure 6, which has a stronger absorption than a passivation 64 on the outer curves. This allows the phase of the mode propagating in the semiconductor layer sequence 10 to be influenced such that a symmetrical radiation profile or far field is generated.

In the 3L and 3M Further examples of mode filter structures 6 with a curved ridge extension direction are shown, which additionally have thickenings 61 on the facets, i.e., the radiation output surface 12 and the side surface 13 opposite the radiation output surface. This allows the power density to be reduced directly at the facets, in particular at the radiation output surface 12, thereby preventing facet damage at high optical powers (COMD).

As in 3L As shown, the widening of the horizontal bridge width in the form of the thickenings 61 can be symmetrical to the bridge 11 at the facets. However, it is also possible that, as in 3M As shown, the thickenings 61 are asymmetrical to the web 11 at the facets, whereby the radiation angle of the laser light source can also be influenced.

In the 4A to 8B schematic spatial representations of laser light sources with semiconductor layer sequences 10 according to further examples are shown, wherein features such as electrodes and functional layers are not shown for the sake of clarity.

The examples according to the 4A to 5D have, as the mode filter structure 6, a ridge 11 with varying ridge heights 110, 110', 110'' along the ridge extension direction AA perpendicular to the main extension plane of the functional layers. The varying ridge height is produced by uneven etching of the semiconductor layer sequence 10 to create the ridge 11, so that the varying ridge heights correspond to inhomogeneous ridge etch depths. Deeper etched regions, i.e. regions with a greater ridge height, reduce the current spreading and improve the overlap of the optical mode with the electrically pumped region. This allows lower laser thresholds and thus good efficiency to be achieved.

Flatter etched areas, i.e. areas with a lower ridge height, can result in weaker waveguiding, so that higher modes experience greater losses and are thus attenuated or no longer guided at all.

As in the 4A, 4D and 5A to 5D As shown, the transitions between the varying ridge heights can be abrupt, for example, kink-like. Alternatively, the transitions in the respective etching depth and thus the transitions in the ridge heights can be designed to be smooth, as shown in the 4B and 4C which can avoid losses in the fundamental mode.

In the 4A In the example shown, the ridge width and the variation of the ridge height 110, 110' are selected such that only one mode is guided in the facet region, i.e., particularly in the area of the radiation output surface 12. The deeper etched regions reduce the current spreading and increase the lateral fill factor, which can improve the laser performance.

In order to achieve wider lateral far fields and thus a lower aspect ratio between vertical and horizontal modes, the ridge can also be etched rather deeply, particularly in the facet region 12, 13. In this case, shallower etched regions with a lower ridge height can be used as a mode filter structure 6 in the center of the resonator formed by the facets 12, 13, i.e. the radiation output surface 12 and the side surface 13 opposite the radiation output surface (see 4B) or at the end of the resonator at the radiation coupling surface 12 against overlying side surface 13 (see 4C ) can be arranged.

In order to set a smaller far-field angle and/or to enable higher output powers, the web 11 can be etched flatter in the facet area, i.e. in particular in the area of the radiation output surface 12, and thus have a lower web height 110'', as in 4D By exchanging the radiation output surface 12 and the side surface 13 opposite the radiation output surface 12, this can also be achieved for the example according to 4C apply.

Due to the lower ridge height, the optical mode expands in this region. This results in additional high losses, especially for higher modes.

As in connection with the 5A to 5D As shown, the mode filter structure 6 can particularly preferably be combined by a varying horizontal web width with thickenings 61 or constrictions 62 with a varying web height 110, 110'.

A low aspect ratio of the emitted laser beam is favored by narrow ridges near the radiation output surface 12 and strong wave guidance due to a high ridge height. This can be combined in the central region with a larger ridge width, which is less strongly index-guided due to a lower ridge height, i.e., a shallower etching depth, as shown in 5A is shown.

In particular, for example, the laser light sources of the examples of 5A and 5C be single-mode over the entire ridge length, because the strong waveguiding in the deeply etched areas with a large ridge height of 110 is compensated by correspondingly narrow horizontal ridge widths. This makes it possible to widen the far-field angle as required, as in the example of the 5A or narrow according to the example according to the 5C Independently of the web width at the facets 12, 13, i.e. in particular at the radiation output surface 12, a lower operating voltage can also be achieved by a larger web width in the form of a thickening 61 in the middle of the web 10 according to 5A or a smaller current spread by a constriction 62 of the horizontal web width in the middle according to the example in 5C can be achieved.

According to the example in 5B and the example in 5D However, the laser light source does not have to be monomode over the entire length of the ridge. In these examples, mode filter structures 6 are used according to the example in 5B resulting in a wider far field or according to the example in 5D resulting in a narrower far field.

According to the example in 6 The ridge 11, as a mode filter structure 6, has different ridge heights 110 and 110' on the ridge side surfaces 111 and 112. As a result, the asymmetric etching depths and the resulting different ridge heights 110, 110' on the two ridge side surfaces 111, 112 allow an asymmetric waveguide to be created that can only carry one mode. At the same time, the deeper etching on one ridge side surface 111 of the ridge 11 with the larger ridge height 110 reduces the current spreading on this side, which leads to an increase in performance while simultaneously maintaining single-mode operation.

In addition to the different web heights 110, 110' on the two sides of the web 11, the web heights can also vary along the web extension direction AA. Furthermore, it is also possible that, for example, as in 6 As shown, in addition to the different web heights 110, 110' on the two web side surfaces 111, 112 of the web 11, the web extension direction AA, AA', AA'' and/or the horizontal or vertical web width varies, whereby a combination of the described effects and advantages can be achieved.

In the examples shown so far, waveguiding is enabled by a refractive index jump between the semiconductor material of the semiconductor layer sequence and the environment, which is formed, for example, by air or a homogeneous passivation layer not shown in the examples. A variation of the refractive index jump is achieved by varying or different ridge heights. As described in connection with the 7 to 8B As shown, such a variation of the refractive index jump can also be achieved by a different passivation 63, 64 on the two web side surfaces 111, 112 and/or by a passivation 63, 64 varying along the web extension direction AA.

As in 7 As shown, different materials can be used for the passivations 63, 64 on the two ridge side surfaces 111, 112 as the mode filter structure 6, while the desired refractive index jump can be set independently as a further part of the mode filter structure 6 by different ridge heights 110, 110' on the ridge side surfaces 111, 112.

In the example according to the 8A the web 11 is passivated in a central area with a different material 64 than in the areas close to the facets, in which the passivation material 63 is arranged. If, for example, the central part is passivated with a material having a lower refractive index than the remaining regions along the extension direction AA of the web 11, this has an effect similar to a greater etching depth and a higher web height in this region. The transition between the passivations 63 and 64 can be abrupt, as in the 8A and 8B is shown. Alternatively, the transition between the passivations 63 and 64 can particularly preferably be selected as a smooth transition. For example, one of the passivations 63, 64 can have a decreasing height, while the additional passivation 64 or 63 located above it has an increasing height.

A combination of the formation of different web heights with the use of different passivation materials and/or different absorbing materials along the web 11 is particularly advantageous. In the case of the web 11 according to the example of 8B , in which the passivation 64 in the deeper etched region with the greater ridge height 110' is selected differently than in the remaining region, this advantageously enables, for example, an absorbing material to be placed selectively along the ridge 11 without changing the mode guidance. If, for example, a more strongly absorbing material 64 is used in the central region, higher modes can be attenuated because this material then also has a higher refractive index. As such a material for the passivation 64, for example, non-stoichiometric, silicon-rich SiO ₂ or SiN can be used, while corresponding stoichiometric SiO ₂ or SiN is used as passivation 63. In order to keep the refractive index jump along the ridge 11 constant, the region passivated with the higher refractive index material 64 is etched correspondingly deeper.

A combination of the mode filter structures 6 of the examples according to the 6 to 8 can make it possible to optimally adjust the mode profile to high efficiency, desired far-field width and single-mode.

In the 9A to 10C Methods for producing laser light sources are shown, which each have a varying vertical ridge width 113, 113' as a mode filter structure 6. The illustrations correspond to a section through the laser light source or the semiconductor layer sequence 10 according to the section plane BB in 1A .

In both procedures, according to the 9A and 10A a semiconductor layer sequence 10 is provided, in which, for the sake of clarity, only the active layer 40 is shown. A hard mask 7 is applied to the semiconductor layer sequence 10 as an etching mask, which in the subsequent etching step according to the 9B and 10B The web width as well as the course of the web, for example, with a varying or straight web extension direction, are defined. The etching of the web 11 is carried out using a dry-chemical etching process.

In the example according to the 9A to 9C To produce the bridge, the active layer 40 is etched so that it forms part of the bridge 11 and side surfaces of the active layer 40 form parts of the side surfaces of the bridge 11. In the example shown, the active layer 40 comprises InGaN. This is etched in a further process step according to 9C laterally undercut by means of a wet-chemical etching process, so that the web 11 in the region of the active layer 40 has a smaller vertical web width 113' compared to the vertical web width 113 of the remaining regions of the web 111. Thus, the vertical web width 113, 113' in the region of the active layer 40 and thus in the active region has a constriction 62.

In the example according to the 10A to 10C the bridge 11 is provided with a 9A to 9C lower ridge height, so that the active layer 40 is not exposed by the ridge 11. Above the active layer 40, a functional layer 46 is present in the semiconductor layer sequence 10, which has at least one InGaN layer or several InGaN layers that have the same or, as in the present example, different In content. By a wet-chemical etching step according to 10C the layer 46 is laterally undercut. The different In contents of the layers of the functional layer 46 result in different etching rates, whereby the web 11 is formed with an undercut and thus with a vertical web width 113, 113' tapering towards the active layer 40 in the form of a constriction 62.

Following the 9C and 10C In both processes, the hard mask 7 is removed after the wet-chemical etching steps shown. An electrode (not shown) is then applied to the web 11. Furthermore, it is also possible to apply a passivation layer, for example, a varying passivation layer according to the previous examples, next to the web 11 produced in each case.

By connecting with the 9A to 10C Using the method shown, it is possible to produce current or mode apertures as a mode filter structure 6 by a combination of wet-chemical and dry-chemical etching processes. Because in both examples an upper part of the ridge is wider than a lower part, which is more relevant for waveguiding, a larger contact area can be created with an electrode applied to the ridge (not shown). This allows the operating voltage of the laser light sources to be reduced, thereby increasing efficiency. This can be particularly important for laser light sources with semiconductor layer sequences 10 based on a GaN material system, since the contact resistances, especially of p-doped layers, are comparatively high in this material system.

In the 11A to 14B Methods for producing laser light sources with mode filter structures 6 are shown, in which the mode filter structures 6 are produced by modifications of the semiconductor layer materials or sequence of the semiconductor layer sequence 10.

In the example according to the 11A to 11C is calculated as in the previous examples according to the 9A to 10C a semiconductor layer sequence 10 is provided, which additionally has a functional layer 47 above the active layer 40, which contains aluminum. After the production of the web 11 by a dry-chemical etching process in the process step according to 11B , in which the functional layer 47 is exposed as part of the web 11, in a further process step the exposed side surfaces of the functional layer 47 are oxidized by an oxidation step, so that the functional layer 47 has an oxidation 471 on the side surfaces of the web 11, which serves as a mode filter structure 6 and thus as a current or mode aperture.

In connection with the 12A to 12C a method for producing a laser light source according to a further example is shown, in which after the provision of the semiconductor layer sequence 10, the application of the hard mask 7 ( 12A) and dry chemical etching to form the web 11 ( 12B) by implantation or a thermal process such as diffusion into the region of the semiconductor layer sequence 10 next to the web 11 and at least partially also below the web 11, a material 65 which changes the conductivity of the semiconductor material and/or is light-absorbing can be introduced. As a result, a mode filter structure 6 which serves as a current and/or mode aperture can be created by means of the introduced material 65. For example, silicon can be introduced as material 65 as a dopant which can change the conductivity of the p-doped semiconductor layers formed above the active layer in the example shown. Alternatively, hydrogen can also be introduced, for example, in order to create an electrically insulating region. By introducing a light-absorbing material such as germanium, the optical properties of the modified region of the semiconductor layer sequence 10 can be changed.

While according to the example in 12C the material is applied in an area above the active layer 40, it is also possible to apply the material 65 up to the active layer or even below the active layer, as in the example of the 12D is shown.

In the 13A to 14B Further examples are shown in which the mode filter structure 6 in the semiconductor layer sequence 10 is produced by damaging the semiconductor material of the semiconductor layer sequence 10 in certain areas.

In the example of 13A and 13B A semiconductor layer sequence 10 is provided in which the semiconductor material is permanently damaged by means of a short-pulse laser beam, in which material is evaporated. Such a method can also be referred to as "stealth dicing". In particular when using a group III-V compound semiconductor material, for example a nitride compound semiconductor material such as InGaN, the group V component in particular can be at least partially evaporated by a focused laser beam, thereby creating a damaged structure 66. The damage or the creation of the damaged structure 66 can be carried out as in 13A shown above the active layer 40, in the example shown in a p-doped region. In a further process step according to 13B the web 11 is produced by dry chemical etching, whereby the damaged structure 66 next to the web 11 is exposed.

In the example according to the 14A and 14B The damaged structure 66 is produced as a mode filter structure 6 below the active layer 40, in the example shown in an n-doped region of the semiconductor layer sequence 10. This can, as in the 14A and 14B shown, after the web has been produced. Alternatively, the areas with the damaged structure 66 can also be created before the web 11 is produced.

Furthermore, it is also possible for the damaged structure 66 to extend into the active layer 40, either from the side above the active layer 40 or from regions below the active layer 40. Furthermore, it is also possible for damaged structures 66 to be created above and below, as well as additionally in, the active layer 40.

In addition to the mode filter structures shown in connection with the examples in the figures, further etching structures may be present next to or in the web area, which may, for example, contain additional absorbing materials in order to suppress higher modes even more strongly.

In the 15A to 15G Further examples of laser light sources with mode filter structures 6 are shown, which additionally act as stray light filters. The stray light can, for example, comprise incoherent light, which is generated in addition to the coherent fundamental mode in the active region. The stray light can also comprise higher modes, which, for example, can oscillate and be guided by the incoherent scattered light in the resonator. By reducing the stray light by the mode filter structures 6 acting as stray light filters, these higher modes can also be suppressed. In addition, the mode filter structures 6 shown have features described in connection with the previous examples, which will therefore not be discussed further below. In particular, the mode filter structures 6 shown in the previous examples can additionally comprise the features described in the 15A to 15G shown scattered light filter structures 67.

At least some of the previously described laser light sources with mode filter structures 6 are based on the fact that higher modes experience greater losses than the fundamental mode and are thus attenuated. These losses can be, for example, scattering losses. This can mean that scattered light is guided in the waveguiding layers of the semiconductor layer sequence 10 next to the ridge 11 and ultimately exits at the radiation output surface 12, which leads to disturbances in the far field. The mode filter structures 6 according to the examples in the 15A to 15G therefore have additional structures 67 acting as scattered light filters next to the web 11. In 15A an exemplary sectional view through a laser light source in the area of the scattered light filter structure 67 is shown, while the 15B to 15G Show top views of the semiconductor layer sequence 10 and the web 11.

This stray light filter structure 67 can, as shown in the 15B to 15G shown, at different positions along the web 11, but is preferably arranged close to the radiation output surface 12. The scattered light filter structure 67 has, for example, a distance of less than 300 µm, preferably less than 100 µm and particularly preferably less than 50 µm from the radiation output surface 12.

The scattered light filter structure 67 may, for example, have or be a depression, for example an etched trench, as in 15A which extends into the waveguiding layers of the semiconductor layer sequence 10 and particularly preferably through the active layer 40 and particularly preferably into a cladding layer located below the active layer 40, for example an n-doped cladding layer. Preferred depths are between 1 nm and 10,000 nm and particularly preferably between 100 nm and 2,000 nm deeper than the active layer 40, the limits being included in each case.

The scattered light filter structures 67 have a distance 114 of 0 µm to 20 µm, preferably from 0 µm to 6 µm and particularly preferably from 1 µm to 3 pm from the web 11. The length 115 of the scattered light filter structure 67 is between 0.1 µm and 500 µm, preferably between 1 µm and 100 µm and particularly preferably between 3 µm and 30 µm, the limits being included in each case. The scattered light filter structures 67 are arranged at least on one side, but preferably on both sides of the web 11 and have various shapes, some of which are shown purely by way of example in the 15B to 15G are shown. The scattered light filter structures 67 are preferably configured such that scattered light is scattered away from the web or absorbed. For this purpose, the scattered light filter structures 67 can preferably be covered by a passivation layer and/or filled with absorbing materials.

The examples of laser light sources with mode filter structures shown in the individual figures can, in particular, also be combined with one another. Particularly preferred combinations of mode filter structures can be a different ridge width, i.e., a varying horizontal and/or vertical ridge width, in combination with a varying ridge height and/or in combination with a varying passivation along the ridge and/or a combination of the latter two features. Furthermore, a combination of at least one of the mentioned features for the mode filter structure with a curved ridge extension direction can be particularly advantageous. The mentioned features, i.e., in particular, at least one or more of the mentioned features for the mode filter structure, can also be particularly advantageous in combination with oxidized partial regions of at least one ridge side surface and/or with materials introduced into the functional layer adjacent to the ridge and/or with damaged regions of at least one functional layer. By combining the various embodiments, examples, and features of the mode filter structure, the advantages of the individual variants can be combined with one another, while disadvantages that the individual variants may have can be eliminated by such combinations. and other additional features of the mode filter structure can be compensated.

This may make it possible for the output power in optical single-mode operation to be increased by the different designs and technological implementation options of the mode filter structure without adversely affecting other laser parameters.

Claims (11)

A laser light source with a ridge waveguide structure, comprising a semiconductor layer sequence (10) with a plurality of functional layers (4) and an active region (45) suitable for generating laser light during operation, wherein at least one of the functional layers (4) is formed as a ridge (11) of the ridge waveguide structure, and wherein the semiconductor layer sequence (10) has a mode filter structure (6) formed perpendicular to a main extension plane of the functional layers (4) below the ridge (11), wherein the main extension plane is perpendicular to an arrangement direction of the semiconductor layer sequence (10), wherein the semiconductor layer sequence (10) has at least one functional layer as a mode filter structure (6), which has a damaged structure (66) produced by evaporating a material of the semiconductor layer sequence (10) with a laser, wherein the laser light source has a further mode filter structure (6), and the further mode filter structure (6) has different Ridge heights (110, 110') on two opposite ridge side surfaces (111, 112), so that an asymmetric waveguide is produced, and wherein the mode filter structures (6) attenuate higher modes that occur in addition to a fundamental mode in the laser light source. Laser light source according to Claim 1 , wherein the horizontal web width (113, 113', 113'') has at least one thickening (61) and/or constriction (62). Laser light source according to one of the preceding claims, wherein the mode filter structure (6) has, in addition to the web (11), at least one scattered light filter structure (67) which has a recess in the semiconductor layer sequence (10). Laser light source according to one of the preceding claims, wherein the web (11) as a mode filter structure (6) has a varying web height (110, 110', 110'') perpendicular to the main extension plane of the functional layers (4), and the web height (110, 110', 110'') varies along a web extension direction (AA). Laser light source according to one of the preceding claims, wherein a passivation (63, 64) is arranged next to the web (11) as a mode filter structure (6), which passivation varies along a web extension direction (AA). Laser light source according to Claim 5 , wherein the web (11) is delimited by the two web side surfaces (111, 112) running along the web extension direction (AA) and different passivations (63, 64) are arranged next to the web (11) as a mode filter structure (6) on the two web surface sides (111, 112). Laser light source according to one of the preceding claims, wherein the web (11) as a mode filter structure (6) has a curved web extension direction (AA, AA', AA''). Laser light source according to one of the preceding claims, wherein the web (11) adjoins a functional layer of the semiconductor layer sequence (10) which has a conductivity-changing and/or light-absorbing material (65) as a mode filter structure (6). Laser light source according to one of the preceding claims, wherein the damaged structure (66) is arranged on a side of the active region (45) facing away from the web (11). Laser light source according to one of the preceding claims, wherein the damaged structure (66) forms a mode aperture. Laser light source according to one of the preceding claims, wherein the epitaxial semiconductor layer sequence comprises a III-V compound semiconductor material, and the group V material in the damaged structure (66) is at least partially evaporated.

Images