µled comprising a multilayer thin-film light outcoupling structure

Abstract

The invention concerns an optoelectronic device, in particular μLED, comprising a semiconductor layer stack of at least a first layer of a first conductivity type, a second layer of a second conductivity type as well as an active region between the first and second layer, wherein the semiconductor layer stack comprises a bottom surface as well as a light emitting surface opposite the bottom surface. The optoelectronic device further comprises a light outcoupling structure arranged above or on the light emitting surface, the light outcoupling structure comprising at least a first, a second and a third layer wherein : at least two of the first, second and third layer comprise a material with a different refractive index; the first, second and third layer comprise a thickness of less than the wavelength of light generated within the semiconductor layer stack when applied with a respective current; and at least two of the first, second and third layer comprise a different thickness.

Description

[0001] 2023PF00082 - 1 - µLED COMPRISING A MULTILAYER THIN-FILM LIGHT OUTCOUPLING STRUCTURE The present application claims priority from German patent application DE 102023 124 036.6 filed on September 06, 2023, the disclosure of 5 which is incorporated by way for reference in its entirety. The present invention concerns an optoelectronic device comprising a multilayer thin-film light outcoupling structure as well as a method for manufacturing the same. 0 BACKGROUND The light emission of a typical µLED is emitted to the farfield (any region beyond the first few µm after the LED) in all directions. For5 many applications, only the emission into a particular solid angle is of interest and thus, any light that is emitted out of the given solid angle is lost for the application. It is also often desired to supress emission to high angles in order to increase the contrast of a µLED. For some embodiments, only the emission into the +-15° forward solid0 angle can be of interest as any other emission is lost. Traditionally, the directionality of incoherent light sources like LEDs is increased via optical devices such as reflectors or lenses, which shape the beam profile of a light source. Notably, such optics are5 often bulky and therefore cause optical loss or limit the design. For µLEDs, on the nanoscale, meta- and microlenses have been introduced to manipulate light by microscopic structures. In addition, scientific work has been conducted towards the development of incoherent and directional light sources based on periodic or random gratings like0 dielectric or plasmonic structures. Moreover, extensive studies regarding metasurfaces have been conducted to increase the directional outcoupling of emitters. However, all of these systems are challenging to fabricate in mass-production or apply5 to coherent light sources only. Notably, they do not affect the light source itself but rather shape the light distribution over angle that exits a light source like an LED package. 2023PF00082 - 2 - It is thus an object of the present application to provide an optoelectronic device, in particular µLED, with an enhanced directional outcoupling of light as well as a method for manufacturing the same. 5 SUMMARY OF THE INVENTION This and other objects are addressed by the subject matter of the independent claims. Features and further aspects of the proposed principles are outlined in the dependent claims. 0 The idea is to use instead of lenses, and instead or in addition to inclined sidewalls and reflective surfaces, an individually tuned multilayer thin-film structure on top of a µLED to increase the directionality and light extraction efficiency of the overall device. 5 The multilayer thin-film structure comprises a structure of layers with alternating materials, i.e., SiO2 and AlInP but other materials can be used for different systems. Every layer has a fine-tuned individual thickness which is specifically designed for every individual application / µLED type. The structure works by using constructive0 interference to promote radiative channels which have a favourable emission direction and extraction efficiency and suppress lossy channels by destructive interference. Such a thin-film structure is particularly appealing since it is easy5 and very precise to manufacture compared to other solutions such as lenses since it consists only of planar layers. Other outcoupling structures involve complicated 3D geometries which are hard to manufacture and usually deviate from the desired shape. Therefore, the actual performance of the µLED is usually compromised due to0 manufacturing defects and the figure of merit smaller than predicted for the ideal structure. Compared to a µLED without any outcoupling structure, a directional outcoupling efficiency can for example by means of such a multilayer thin-film structure increase of 50-200%. 5 According to a first aspect, an optoelectronic device, in particular µLED, is provided. The optoelectronic device comprises a semiconductor layer stack of at least a first layer of a first conductivity type, a 2023PF00082 - 3 - second layer of a second conductivity type as well as an active region between the first and second layer. The semiconductor layer stack comprises a bottom surface as well as a light emitting surface opposite the bottom surface. 5 The optoelectronic device can in particular be or comprise a small light emitting component / element such as a small LED or µLED. A µLED can in particular be a very small LED with edge lengths down to 30 µm, down to 10 µm, down to 5 µm or even less. Such small LEDs can be free0 of a growth substrate and require a special handling and processing to improve their IQE and light outcoupling efficiency. One approach to improve the IQE of the µLED is to cover side walls or side wall portions of the µLED with a regrowth layer. A possible approach to improve the outcoupling efficiency and light directionality of the light emitted5 by the µLED is to provide outcoupling structures and / or reflective structures on / in the µLED. According to some aspects, the semiconductor layer stack comprises a semiconductor material such as for example Indium Gallium Aluminium0 Phosphide (InGaAlP), Gallium Nitride (GaN), Gallium Arsenide (GaAs), Aluminium Gallium Nitride (AlGaN), or any other semiconductor materials suitable for the manufacturing light emitting components. The semiconductor layer stack comprises at least a first layer of a first conductivity type, a second layer of a second conductivity type as well5 as an active region between the first and second layer. The first layer can for example be a semiconductor layer that is n-doped, whereas the second layer can for example be a semiconductor layer that is p-doped. The two layers can thus form a pn-junction with the active region arranged in-between. The active region can for example comprise a0 quantum well or multi quantum well structure, or can for example comprise quantum dots. In addition, a light outcoupling structure is arranged above or on the light emitting surface, wherein the light outcoupling structure5 comprises at least a first, a second and a third layer. At least two of the first, second and third layer thereby comprise a material with a different refractive index, the first, second and third layer 2023PF00082 - 4 - comprise a thickness of less than the wavelength of light generated within the semiconductor layer stack when applied with a respective current, and at least two of the first, second and third layer comprise a different thickness. 5 In particular the material chosen for the first, second and third layer, as well as the thicknesses of the first, second and third layer is individually chosen, to meet the respective requirements of the application, the optoelectronic device is used for, as well as with0 regard to the configuration of the semiconductor layer stack. By means of individually choosing the material as well as the thicknesses of the first, second and third layer, the directionality and light extraction efficiency of the optoelectronic device can be increased, and in some aspects, even selective wavelength emission, i.e., emission5 of light within a very small wavelength range, can be achieved by the optoelectronic device. For a DBR in contrast the rule for the thicknesses of its layers is given by λ / 4. For the light outcoupling structure it is proposed to0 have no clear solution or rule for the thickness but to individually choose the thickness of the separate layers. In particular the light outcoupling structure is not a DBR. According to some aspects, the light outcoupling structure is5 configured to directly transmit substantially only light that deviates from a perpendicular to the light emitting surface only by a maximum of ± 20 degrees, in particular ± 15 degrees. In particular only light impinging the light outcoupling structure that deviates from a perpendicular to the light emitting surface only by a maximum of ± 200 degrees, in particular ± 15 degrees is directly transmitted through the light outcoupling structure and thus exits the light outcoupling structure within more or less the same angle. In addition, at least some light impinging the outcoupling structure that deviates from a perpendicular to the light emitting surface by more than ± 20 degrees,5 in particular more than ± 15 degrees can be reflected / bent such that it exits the light outcoupling structure with an angle that deviates from a perpendicular to the light emitting surface only by a maximum 2023PF00082 - 5 - of ± 20 degrees, in particular ± 15 degrees. Hence the light outcoupling structure can on the one hand act as kind of a incidence angle dependent filter as well as an optical element for partially collimating light incident on the light outcoupling structure. 5 According to some aspects, the light outcoupling structure comprises a band pass characteristic with a full-width at half-maximum of no more than 50 nm, in particular no more than 25 nm. The light outcoupling structure can in particular be configured to transmit only or0 substantially only light of a wavelength within a very small wavelength range, for example the wavelength range being not greater than 50 nm and in particular not greater than 25 nm. The full-width at half- maximum describes the spectral bandwidth over which a bandpass filter is light-transmissive. The upper and lower limits of the bandwidth are5 defined as the wavelength at which the filter exhibits 50% of the maximum transmission. For example, if the maximum transmission of the filter is 90%, then the wavelength at which the filter has 45% transmission describes the upper and lower limits of the full-width at half-maximum. A full-width at half-maximum of 10 nm or less can be0 referred to as narrowband and can for example be used for laser line purification or chemical detection. A full-width at half-maximum of 25-50 nm can for example be used in imaging applications, while a full- width at half-maximum greater than 50 nm can be referred to as broadband and can for example be used in fluorescence microscopy. 5 According to some aspects, the first, second and third layer are individually tuned such that the light outcoupling structure directly transmits substantially only light that deviates from a perpendicular to the light emitting surface only by a maximum of ± 20 degrees, in0 particular ± 15 degrees and such that the light outcoupling structure provides a band pass characteristic with a full-width at half-maximum of no more than 50 nm, in particular no more than 25 nm. Hence the light outcoupling structure can on the one hand enhance the directionality of outcoupled light as well as reduce the wavelength5 range of the light being outcoupled to a small or narrow wavelength range. 2023PF00082 - 6 - According to some aspects, the light outcoupling structure comprises several layers of two materials with a different refractive index arranged in an alternating order. The light outcoupling structure can in particular comprises a structure of layers with alternating 5 materials, ie. SiO2, TiO2, Nb2O5, Al2O3 and AlInP but other materials can be used for different systems. A maximum refractive index jump between adjacent layers of the light outcoupling structure can for example be 2.5. 0 According to some aspects, the optoelectronic device further comprises a reflective structure surrounding the at least one semiconductor layer stack in a circumferential direction. The reflective structure exposes at least the light emitting surface and in particular extends at least from a level of the light emitting surface into the direction away from5 the light emitting surface protruding the light emitting surface. Light emitted from the semiconductor layer stack under a very shallow angle can by means of the reflective structure for example be reflected to be able to be directed by the light outcoupling structure before outcoupled from the light outcoupling structure under a desire angle. 0 As an alternative the light can be reflected back by the light outcoupling structure into the semiconductor layer stack, transmit through the semiconductor layer stack and be reflected by an optional mirror encapsulating the semiconductor layer stack on surfaces other than the light emitting surface. Thus, light generated within the5 semiconductor layer stack can be reflected within the optoelectronic device and undergoes with multiple internal reflections until being outcoupled from the light outcoupling structure under a desire angle. According to some aspects, the reflective structure extends from a0 level between the bottom surface and the active region until a level above the light emitting surface. Again, light emitted from the semiconductor layer stack under a very shallow angle, even close to horizontally emitted light, can by means of the reflective structure for example be reflected to be able to be directed into the direction5 of the light outcoupling structure before outcoupled from the light outcoupling structure under a desire angle. As an alternative the light can be reflected back by the light outcoupling structure into the 2023PF00082 - 7 - semiconductor layer stack, transmit through the semiconductor layer stack and be reflected by an optional mirror encapsulating the semiconductor layer stack on surfaces other than the light emitting surface. Thus, light generated within the semiconductor layer stack 5 can be reflected within the optoelectronic device in a and undergoes with multiple internal reflections until being outcoupled from the light outcoupling structure under a desire angle. According to some aspects, the reflective structure surrounds the light0 outcoupling structure in a circumferential direction. In particular the reflective structure can form a recess above the light emitting surface and the light outcoupling structure can be arranged within this recess latterly filling the recess. The light outcoupling structure may form a planar surface with the reflecting structure on an upper5 surface, but the reflecting structure may also project above the light outcoupling structure or vice versa. According to some aspects, the optoelectronic device further comprises a mirror structure arranged below the bottom surface and / or adjacent0 to sidewalls of the semiconductor layer stack, wherein the sidewalls are connecting the bottom surface with the light emitting surface. The mirror structure can for example be of a reflective coating and / or a regrowth layer and / or electric contact(s) and / or a reflective encapsulation material. By means of the reflective structure, an5 optical cavity can be formed by means of which light emitted or reflected into the direction of the sidewalls and / or the bottom surface can be reflected back into the direction of the light outcoupling structure. 0 According to some aspects, the optoelectronic device is free of a lens or a similar optical element. In particular the optoelectronic device can comprise only the light outcoupling structure in form of several layers as an optical element for enhancing the directionality of light being emitted by the optoelectronic device. 5 According to some aspects, the first, second and third layer comprise at least two of: 2023PF00082 - 8 - SiO2; AlInP; TiO2; Nb2O5; and 5 Al2O3. According to a further aspect, a method for manufacturing an optoelectronic device, in particular optoelectronic device according to at least some of aforementioned aspects, is provided. The method0 comprises the steps: providing a semiconductor layer stack of at least a first layer of a first conductivity type, a second layer of a second conductivity type as well as an active region between the first and second layer, wherein the semiconductor layer stack comprises a bottom surface as well as a5 light emitting surface opposite the bottom surface; and providing a light outcoupling structure above or on the light emitting surface, the light outcoupling structure comprising at least a first, a second and a third layer wherein • at least two of the first, second and third layer comprise a0 material with a different refractive index; • the first, second and third layer comprise a thickness of less than the wavelength of light generated within the semiconductor layer stack when applied with a respective current; and 5 • at least two of the first, second and third layer comprise a different thickness. According to some aspects, the step of providing the light outcoupling structure comprises a step of determining a thickness and / or material0 combination of the first, second and third layer based on the emission characteristic of light emitted through the light emitting surface and / or based on the material and / or shape of the semiconductor layer stack and / or based on the use of the optoelectronic device. For each emission characteristic of light emitted through the light emitting5 surface and / or each material and / or shape of the semiconductor layer stack and / or each use of the optoelectronic device, the thickness 2023PF00082 - 9 - and / or material combination of the first, second and third layer can be individually tuned. According to some aspects, the thickness and / or material combination 5 of the first, second and third layer is determined such that the light outcoupling structure is configured to directly transmit substantially only light that deviates from a perpendicular to the light emitting surface only by a maximum of ± 20 degrees, in particular ± 15 degrees. As already described for the optoelectronic device, the light0 outcoupling structure can be configured such that only light impinging the light outcoupling structure that deviates from a perpendicular to the light emitting surface only by a maximum of ± 20 degrees, in particular ± 15 degrees is directly transmitted through the light outcoupling structure and thus exits the light outcoupling structure5 within more or less the same angle. In addition, the light outcoupling structure can be configured such that at least some light impinging the outcoupling structure that deviates from a perpendicular to the light emitting surface by more than ± 20 degrees, in particular more than ± 15 degrees can be reflected / bent such that it exits the light0 outcoupling structure with an angle that deviates from a perpendicular to the light emitting surface only by a maximum of ± 20 degrees, in particular ± 15 degrees. By means of the step of determining a respective thickness and / or material combination of the first, second and third layer, such a configuration of the light outcoupling5 structure can be achieved. According to some aspects, the thickness and / or material combination of the first, second and third layer is determined such that the light outcoupling structure comprises a band pass characteristic with a full-0 width at half-maximum of no more than 50 nm, in particular no more than 25 nm. Again, by means of the step of determining a respective thickness and / or material combination of the first, second and third layer, such a configuration of the light outcoupling structure can be achieved. 5 SHORT DESCRIPTION OF THE DRAWINGS 2023PF00082 - 10 - Further aspects and embodiments in accordance with the proposed principle will become apparent in relation to the various embodiments and examples described in detail in connection with the accompanying drawings in which 5 Fig. 1A and 1B each show a cross section of an optoelectronic device in accordance with some aspects of the proposed principle; 0 Fig. 2A and 2B illustrate the reflectivity characteristics of a light outcoupling structure in accordance with some aspects of the proposed principle with regard to the angle of incidence of light incident on the5 light outcoupling structure; Fig. 3 illustrates the reflectivity characteristics of a light outcoupling structure in accordance with some aspects of the proposed principle with regard to0 the angle of incidence as well as the wavelength of light incident on the light outcoupling structure; Fig. 4 shows the light intensity in the 2D farfield of5 light emitted by an optoelectronic device in accordance with some aspects of the proposed principle; and Fig. 5 shows the light intensity in the 3D farfield of0 light emitted by an optoelectronic device in accordance with some aspects of the proposed principle. DETAILED DESCRIPTION 5 The following embodiments and examples disclose various aspects and their combinations according to the proposed principle. The embodiments 2023PF00082 - 11 - and examples are not always to scale. Likewise, different elements can be displayed enlarged or reduced in size to emphasize individual aspects. It goes without saying that the individual aspects of the embodiments and examples shown in the figures can be combined with each 5 other without further ado, without this contradicting the principle according to the invention. Some aspects show a regular structure or form. It should be noted that in practice slight differences and deviations from the ideal form may occur without, however, contradicting the inventive idea. 0 In addition, the individual figures and aspects are not necessarily shown in the correct size, nor do the proportions between individual elements have to be essentially correct. Some aspects are highlighted by showing them enlarged. However, terms such as "above", “over”,5 "below", "under" "larger", "smaller" and the like are correctly represented with regard to the elements in the figures. So it is possible to deduce such relations between the elements based on the figures. 0 Figures 1A and 1B each show a cross sectional view of an optoelectronic device 1 in accordance with some aspects of the proposed principle. The optoelectronic device 1 comprises a carrier substrate 12 and a contact layer 10 arranged on the carrier substrate 12. Arranged on the contact layer 10 within a cavity of the contact layer 10 and5 electrically coupled to contact layer 10 is a light generating structure, in particular µLED. The light generating structure comprises a semiconductor layer stack 3 of a first layer 4 of a first conductivity type, a second layer 5 of a0 second conductivity type as well as an active region 6 between the first and second layer 4, 5. The semiconductor layer stack 3 is formed such that it comprises a light emitting surface 8, a bottom surface 7 opposite the light emitting surface 6a and first side wall portions 11 extending from the bottom surface 8 into the direction of the light5 emitting surface 7. The first side wall portions 11 thereby comprise portions, in particular side portions of the first layer 4, the second layer 5 and the active region 6. 2023PF00082 - 12 - The light generating structure further comprises a regrowth layer 19 grown on and covering the bottom surface 7 and the first side wall portions 11 and extends in the embodiment shown onto a surface of the 5 second layer 5 adjacent to the first side wall portions 11. In addition, the light generating structure comprises a bottom contact element 15 arranged on the regrowth layer 19 opposite the first layer 4 and follows the regrowth layer 19 along the first side wall portions 11 more or less encapsulating the regrowth layer 19 in the area of the bottom0 surface 8 and the first side wall portions 11. Besides the first side wall portions 11 of the semiconductor layer stack 3, the light generating structure comprises second side wall portions different from the first side wall portions extending through5 the second layer 5, the regrowth layer 19 and the bottom contact element 15 until a continuous residue of the second layer 5, the second side wall portions in the embodiment shown comprising portions, in particular side portions, of the bottom contact element 15, the regrowth layer 19 and the second layer 5. 0 Hence, the first side wall portions 11 are formed by the semiconductor layer stack 3, whereas the second side wall portions are formed by the bottom contact element 15, the regrowth layer 19 and the second layer 5 of the semiconductor layer stack 3. 5 The light generating structure is embedded in an isolation layer 14 arranged between the contact layer 10 and the light generating structure. The isolation layer 14 encapsulates the light generating structure in the circumferential direction U and extends partially onto0 the bottom contact element 15 opposite the bottom surface 7. The isolation on the one hand holds all components in place and prevents a short within the optoelectronic device 1. The isolation layer 14 can for example be of a reflective or light transmissive material. 5 On top of the continuous residue of the second layer 5, a reflective structure 13 surrounding the light emitting surface 8 of the semiconductor layer stack 3 in a circumferential direction U is 2023PF00082 - 13 - arranged, wherein the reflective structure 13 exposes the light emitting surface 8 and extends from a level of the light emitting surface 8 to a level above the light emitting surface 8. “Above the light emitting surface 8” can for example mean above the light emitting 5 surface 8 in a direction from the bottom surface 7 to the light emitting surface 8 after the light emitting surface 8. Hence the reflective structure 13 protrudes the light generating structure in a direction from the bottom surface 7 to the light emitting surface 8. The outcoupling efficiency and directionality of emitted light L of the0 optoelectronic device 1 can by means of the reflective structure 13 be enhanced. The reflective structure 13 is in particular in the form of a ring surrounding the light emitting surface 8 with tapered inner side surfaces, to guide / reflect the light generated within the light5 generating structure in a desired direction. Together with the bottom contact element 10, which in the embodiment shown is of a reflective material, the reflective structure 13 forms a mirror structure, guiding / reflecting the light generated within the light generating structure in a desired direction. 0 To further enhance at least the directionality of outcoupled light L of the optoelectronic device 1, the optoelectronic device 1 further comprises a light outcoupling structure 2 arranged on the light emitting surface 8 within a recess formed by the reflective structure5 13. In the embodiment shown in Fig. 1A, the light outcoupling structure 2 comprises a first, a second and a third layer 9a, 9b, 9c arranged above each other. In the embodiment shown in Fig. 1B, the light outcoupling structure 2 comprises a first, a second, a third, a fourth and a fifth layer 9a, 9b, 9c, 9d, 9e arranged above each other. The0 number of layers is however only to be understood as exemplary and can regarding the specific use be chosen in any other way as well. The idea of the invention now is that the layers of the light outcoupling structure 2 can be individually tuned forming an5 individually tuned multilayer thin-film structure on top of the light generating structure to at least increase the directionality and light extraction efficiency of the overall device. In addition the multilayer 2023PF00082 - 14 - thin-film structure on top of the light generating structure can be configured to act as a wavelength filter configured to transmit only light of a narrow wavelength range. The multilayer thin-film structure comprises a structure of layers with alternating materials, ie. SiO2 5 and AlInP but other materials can be used for different systems. Every layer has a fine-tuned individual thickness which is specifically designed for every individual application / light generating structure type. The structure works by using constructive interference to promote radiative channels which have a favourable emission direction and0 extraction efficiency and suppress lossy channels. Such a thin-film structure is particularly appealing since it is easy and very precise to manufacture compared to other solutions such as lenses since it consists only of planar layers. Compared to a comparable5 optoelectronic device without any outcoupling structure, a directional outcoupling efficiency can for example by means of such a multilayer thin-film structure increase of 50-200%. An electrically contacting of the optoelectronic device 10 can be done0 via the contact layer 10 as well as the reflective structure 13, however ta top contact can also be provided on the second layer 5 in an area adjacent to the reflective structure 13. The embodiments shown show only a single light generating structure5 comprised in the optoelectronic device 1, however one optoelectronic device 1 can also comprise several light generating structures next to each other, being surrounded by a single reflective structure 13 or each being surrounded by a separate reflective structure 13. For example, it is conceivable that three light generating structures are0 surrounded by one reflective structure 13, wherein the three light generating structures are configured to emit red, green and blue light together forming an RGB pixel. It is for example also conceivable that several similar light generating structures are provided and surrounded by a single reflective structure 13, to either provide brighter light5 of a respective wavelength or to provide a “backup” light generating structure in case the other light generating structure(s) is damaged. This is however only to be understood exemplary and the number of light 2023PF00082 - 15 - generating structures can be chosen differently as well as the wavelength of light being emitted by the light generating structures 1. Also, the electrical contacting of several light generating structures can vary in such that all or some of the light generating 5 structures can be operated individually and / or all or some of the light generating structures can be connected such that they are simultaneously operated. Fig. 2A and 2B illustrate the reflectivity characteristics of a light0 outcoupling structure 2 in accordance with some aspects of the proposed principle with regard to the angle of incidence of light incident on the light outcoupling structure 2. Fig. 2A shows a schematic sketch of a light outcoupling structure 2 arranged on a semiconductor layer stack 3. The angle of incidence ϑ of light incident on the light outcoupling5 structure 2 is thereby shown in the lower part, whereas the respective reflectivity characteristic of the light outcoupling structure 2 is shown in the upper part. It is thereby differentiated between light that deviates from a perpendicular Z to the light emitting surface 8 only by a maximum of a defined target angle of incidence ϑtand light0 that deviates from a perpendicular Z to the light emitting surface 8 only by a maximum of a defined critical angle of incidence ϑc. The light outcoupling structure 2 is now designed / configured such that for light that deviates from a perpendicular Z to the light emitting surface 8 only by a maximum of a defined target angle of incidence ϑtthe light5 outcoupling structure 2 comprises a (very) low reflectivity, indicated by the “area” of low reflectivity 16a, whereas for light that deviates from a perpendicular Z to the light emitting surface 8 only by a maximum of a defined critical angle of incidence ϑcthe light outcoupling structure 2 comprises a high(er) reflectivity, indicated by the “area”0 of high reflectivity 16b. The critical angle of incidence ϑcas well as the target angle of incidence ϑtcan thereby with regard to the application be freely chosen. Fig. 2B shows a respective diagram showing the reflectivity of the5 light outcoupling structure with regard to the angle of incidence ϑ of light incident on the light outcoupling structure 2. The reflectivity is thereby shown in percentage, whereas 1 means a reflectivity of 2023PF00082 - 16 - substantially 100%. In the diagram, a first curve 17 shows the reflection characteristic of a light outcoupling structure according to some aspects of the proposed principle, and a second curve 18 shows the reflection characteristic of an anti-reflection coating that can 5 be applied to the light emitting surface as a substitute. It can be seen that by means of the light outcoupling structure a higher reflectivity for incident light with an angle larger than the target angle of incidence ϑtcan be achieved, thus resulting in a higher directionality of the light emitted by the optoelectronic device.0 Fig. 3 illustrates the reflectivity characteristics of an exemplary light outcoupling structure 2 in accordance with some aspects of the proposed principle with regard to the angle of incidence as well as the wavelength of light incident on the light outcoupling structure. 5 The reflectivity is thereby shown in percentage, whereas 1 means a reflectivity of substantially 100%. Form Fig. 3 it can be seen in addition to the diagram shown in Fig. 2B, that besides the higher reflectivity for incident light with an angle larger than the target angle of incidence ϑt, which in the embodiment shown is at around ± 100 degrees, the light outcoupling structure 2 is also sensitive to the wavelength of incident light. As well as for the angle of incidence, the reflectivity of the light outcoupling structure 2 can be higher for light with wavelength differentiating more than a desired value from a target value. In the embodiment shown, the target value for the5 wavelength to be transmitted can for example be 600nm and the light outcoupling structure 2 can be configured to reflect substantially all light that deviates more than 25nm from that target value. Fig. 4 shows a respective light intensity of light emitted by an0 optoelectronic device in accordance with some aspects of the proposed principle in the 2D farfield exemplary for several wavelengths, as well as the averaged light intensity over all wavelengths in comparison to a similar optoelectronic device without a light outcoupling structure. It can be seen that compared to a device without the outcpoupling5 structure, the intensity in the farfield is lower in the direction of interest. This demonstrates the effect of the outcoupling structure on the farfield emission. 2023PF00082 - 17 - Fig. 5 in addition shows a respective light intensity of light emitted by an optoelectronic device in accordance with some aspects of the proposed principle in the 3D farfield. It can be seen that by means of 5 an outcoupling structure as proposed the intensity of light in the farfield can be greatly increased in an area that deviates by only ± 15 degrees from a perpendicular to the light emitting surface.

[0002] 2023PF00082 - 18 - LIST OF REFERENCES 1 optoelectronic device 2 light outcoupling structure 5 3 semiconductor layer stack 4 first layer 5 second layer 6 active region 7 bottom surface 0 8 light emitting surface 9a, 9b, 9c, 9d, 9e layer 10 contact layer 11 side wall portion 12 carrier substrate 5 13 reflective structure 14 isolation layer 15 bottom contact layer 16a, 16b area 17 curve 0 18 curve 19 regrowth layer L Light U circumferential direction5 Z perpendicular ϑ, ϑt, ϑcangle of incidence 0

Claims

2023PF00082 - 19 - CLAIMS 1. Optoelectronic device (1), in particular µLED, comprising: a semiconductor layer stack (3) of at least a first layer (4) 5 of a first conductivity type, a second layer (5) of a second conductivity type as well as an active region (6) between the first and second layer (4, 5), wherein the semiconductor layer stack (3) comprises a bottom surface (7) as well as a light emitting surface (8) opposite the bottom surface (7); and 0 a light outcoupling structure (2) arranged above or on the light emitting surface (8), the light outcoupling structure (2) comprising at least a first, a second and a third layer (9a, 9b, 9c) wherein • at least two of the first, second and third layer (9a,5 9b, 9c) comprise a material with a different refractive index; • the first, second and third layer (9a, 9b, 9c) comprise a thickness of less than the wavelength of light generated within the semiconductor layer stack when applied with a0 respective current; and • at least two of the first, second and third layer (9a, 9b, 9c) comprise a different thickness.

2. Optoelectronic device (1) according to claim 1, 5 wherein the light outcoupling structure (2) is configured to directly transmit substantially only light (L) that deviates from a perpendicular (Z) to the light emitting surface (8) only by a maximum of ± 20 degrees, in particular ± 15 degrees. 0 3. Optoelectronic device (1) according to claim 1 or 2, wherein the light outcoupling structure (2) comprises a band pass characteristic with a full-width at half-maximum of no more than 50 nm, in particular no more than 25 nm. 5 4. Optoelectronic device (1) according to any one of the preceding claims,2023PF00082 - 20 - wherein the first, second and third layer (9a, 9b, 9c) are individually tuned such that the light outcoupling structure (2) directly transmits substantially only light (L) that deviates from a perpendicular (Z) to the light emitting surface (8) only by a 5 maximum of ± 20 degrees, in particular ± 15 degrees and such that the light outcoupling structure (2) provides a band pass characteristic with a full-width at half-maximum of no more than 50 nm, in particular no more than 25 nm. 0 5. Optoelectronic device (1) according to any one of the preceding claims, wherein the light outcoupling structure (2) comprises several layers (9a, 9b, 9c, …) of two materials with a different refractive index arranged in an alternating order. 5 6. Optoelectronic device (1) according to any one of the preceding claims, further comprising a reflective structure (13) surrounding the at least one semiconductor layer stack (3) in a circumferential0 direction (U), wherein the reflective structure (13) exposes at least the light emitting surface (8).

7. Optoelectronic device (1) according to claim 6, wherein the reflective structure (13) extends from a level between5 the bottom surface (7) and the active region (6) until a level above the light emitting surface (8).

8. Optoelectronic device (1) according to any one of the preceding claims, 0 further comprising a mirror structure (10) arranged below the bottom surface (7) and / or adjacent to sidewalls (11) of the semiconductor layer stack (3), the sidewalls (11) connecting the bottom surface (7) with the light emitting surface (8). 5 9. Optoelectronic device (1) according to any one of the preceding claims, wherein the optoelectronic device (1) is free of a lens.2023PF00082 - 21 - 10. Optoelectronic device (1) according to any one of the preceding claims, wherein the first, second and third layer (9a, 9b, 9c) comprise at least two of: 5 SiO2; AlInP; TiO2; Nb2O5; and Al2O3. 0 11. Method for manufacturing an optoelectronic device (1), in particular optoelectronic device (1) according to one of the preceding claims, the method comprising the steps: providing a semiconductor layer stack (3) of at least a first5 layer (4) of a first conductivity type, a second layer (5) of a second conductivity type as well as an active region (6) between the first and second layer (4, 5), wherein the semiconductor layer stack (3) comprises a bottom surface (7) as well as a light emitting surface (8) opposite the bottom surface (7); and 0 providing a light outcoupling structure (2) above or on the light emitting surface (8), the light outcoupling structure (2) comprising at least a first, a second and a third layer (9a, 9b, 9c) wherein • at least two of the first, second and third layer (9a,5 9b, 9c) comprise a material with a different refractive index; • the first, second and third layer (9a, 9b, 9c) comprise a thickness of less than the wavelength of light generated within the semiconductor layer stack when applied with a0 respective current; and • at least two of the first, second and third layer (9a, 9b, 9c) comprise a different thickness.

12. Method according to claim 11, 5 wherein the step of providing the light outcoupling structure (2) comprises determining a thickness and / or material combination of the first, second and third layer (9a, 9b, 9c) based on the emission2023PF00082 - 22 - characteristic of light (L) emitted through the light emitting surface (8).

13. Method according to claim 12, 5 wherein the thickness and / or material combination of the first, second and third layer (9a, 9b, 9c) is determined such that the light outcoupling structure (2) is configured to directly transmit substantially only light (L) that deviates from a perpendicular (Z) to the light emitting surface (8) only by a maximum of ± 200 degrees, in particular ± 15 degrees.

14. Method according to claim 12 or 13, wherein the thickness and / or material combination of the first, second and third layer (9a, 9b, 9c) is determined such that the5 light outcoupling structure (2) comprises a band pass characteristic with a full-width at half-maximum of no more than 50 nm, in particular no more than 25 nm.

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